SC 13D/A

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Amendment No. 1 to

SCHEDULE 13D

Under the Securities Exchange Act of 1934

SYNEOS HEALTH, INC.

(Name of Issuer)

Class A Common Stock, par value $0.01 per share

(Title of Class of Securities)

45329R109

(CUSIP Number)

Michael J. Aiello, Esq.

Sachin Kohli , Esq.

Weil, Gotshal & Manges LLP

767 Fifth Avenue

New York, NY 10153

(212) 310-8000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

August 9, 2018

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because § 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g) check the following box ☐.

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form

with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (the “Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Thomas H. Lee Advisors, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			19,239,664
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			19,239,664
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	19,239,664
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	18.70% (1)
14	TYPE OF REPORTING PERSON
	OO

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Thomas H. Lee Equity Fund VI, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			3,029,630
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			3,029,630
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	3,029,630
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	2.94% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Thomas H. Lee Parallel (DT) Fund VI, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			358,357
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			358,357
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	358,357
12	CHECK  IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	0.35% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	THL Operating Partners, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			5,399
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			5,399
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	5,399
12	CHECK  IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	0.01% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Great-West Investors, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			15,515
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			15,515
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	15,515
12	CHECK  IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	0.02% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Putnam Investments Employees’ Securities Company III, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			15,502
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			15,502
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	15,502
12	CHECK  IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	0.02% (1)
14	TYPE OF REPORTING PERSON
	OO

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	THL Coinvestment Partners, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			28,433
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			28,433
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	28,433
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	0.03% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Thomas H. Lee Parallel Fund VI, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			2,051,504
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			2,051,504
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	2,051,504
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	1.99% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	THL Equity Fund VII Investors (inVentiv), L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			9,323,549
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			9,323,549
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	9,323,549
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	9.06% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Thomas H. Lee Equity Fund VII, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			1,429,259
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			1,429,259
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	1,429,259
12	CHECK  IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	1.39% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Thomas H Lee Parallel Fund VII, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			1,127,743
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			1,127,743
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	1,127,743
12	CHECK  IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	1.10% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	Thomas H. Lee Parallel (Cayman) Fund VII, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	CAYMAN ISLANDS
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			1,511,529
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			1,511,529
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	1,511,529
12	CHECK  IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	1.47% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	THL Executive Fund VII, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			125,282
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			125,282
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	125,282
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	0.12% (1)
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

CUSIP No. 45329R109 13D

1	NAMES OF REPORTING PERSONS
	THL Fund VII Coinvestment Partners, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP			(a)	☐
				(b)	☒
3	SEC USE ONLY
4	SOURCE OF FUNDS
	OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(D) OR 2(E):				☐
6	CITIZENSHIP OR PLACE OF ORGANIZATION
	DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:		7	SOLE VOTING POWER
			0
		8	SHARED VOTING POWER
			217,962
		9	SOLE DISPOSITIVE POWER
			0
		10	SHARED DISPOSITIVE POWER
			217,962
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	217,962
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES				☐
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
	0.21%
14	TYPE OF REPORTING PERSON
	PN

(1) The percent of class was calculated based on 102,911,079 shares of Class A common stock outstanding as of August 6, 2018, as disclosed in the Issuer’s prospectus supplement filed with the SEC on August 8, 2018.

This Amendment No. 1 (“Amendment No. 1”) amends and supplements the statement on Schedule 13D originally filed by the Reporting Persons on August 10, 2017 (the “Schedule 13D”).  Unless otherwise indicated, each capitalized term used but not defined in this Amendment No. 1 shall have the meaning assigned to such term in the Schedule 13D.

Item 1. Security and Issuer

This Schedule 13D relates to the Reporting Persons’ (as defined in Item 2) beneficial ownership interest in the Class A Common Stock, par value $0.01 per share (the “Syneos Common Stock”), of Syneos Health, Inc. (the “Issuer”). The address of the principal executive office of the Issuer is 3201 Beechleaf Court, Suite 600, Raleigh, North Carolina 27604.

Item 4. Purpose of Transaction

Item 4 is supplemented as follows:

On August 9, 2018, Thomas H. Lee Equity Fund VI, L.P., Thomas H. Lee Parallel Fund VI, L.P., Thomas H. Lee Parallel (DT) Fund VI, L.P., Great-West Investors, L.P., Putnam Investments Employees’ Securities Company III, LLC, THL Coinvestment Partners, L.P. and THL Operating Partners, L.P. (the “THL Selling Stockholders”) sold 6,000,000 shares of Syneos Common Stock to Morgan Stanley & Co. LLC (“Morgan Stanley”) at a price of $49.73 per share in a registered offering (the “Offering”).  The Offering closed on August 9, 2018.

In connection with the Offering, the THL Funds entered into a lock-up agreement (a “Lock-up Agreement”) with Morgan Stanley. Under the Lock-up Agreement, the THL Funds generally agreed, subject to certain exceptions, not to sell, transfer or otherwise dispose of any shares of Syneos Common Stock or securities convertible into, or exchangeable or exercisable for, shares of Syneos Common Stock, for 30 days after the date of the final prospectus relating to the Offering without first obtaining the written consent of Morgan Stanley. The Lock-up Agreement is filed as Exhibit 99.3 hereto.

Item 5. Interest in Securities of the Issuer

(a)(b) As of the date hereof, the Reporting Persons beneficially own, in the aggregate, 19,239,664 shares of Syneos Common Stock, which represents 18.70% of Syneos Common Stock issued and outstanding.  The following table sets forth the number and percentage of Syneos Common Stock owned by each Reporting Persons named in Item 2 of this Schedule 13D.  The percentage of Syneos Common Stock owned was calculated based upon 102,911,079 shares outstanding as of August 6, 2018, as disclosed to the Reporting Persons by the Issuer.

Reporting Persons	Number of Shares Beneficially Owned		Percentage of Common Stock
Thomas H. Lee Advisors, LLC		19,239,664		18.70	%
Thomas H. Lee Equity Fund VI, L.P.		3,029,630		2.94	%
Thomas H. Lee Parallel (DT) Fund VI, L.P.		358,357		0.35	%
THL Operating Partners, L.P.		5,399		0.01	%
Great-West Investors, L.P.		15,515		0.02	%
Putnam Investments Employees’ Securities Company III, LLC		15,502		0.02	%
THL Coinvestment Partners, L.P.		28,433		0.03	%
Thomas H. Lee Parallel Fund VI, L.P.		2,051,504		1.99	%
THL Equity Fund VII Investors (Inventiv), L.P.		9,323,549		9.06	%
Thomas H. Lee Equity Fund VII, L.P.		1,429,259		1.39	%
Thomas H. Lee Parallel Fund VII, L.P.		1,127,743		1.10	%
Thomas H. Lee Parallel (Cayman) Fund VII, L.P.		1,511,529		1.47	%
THL Executive Fund VII, L.P.		125,282		0.12	%
THL Fund VII Coinvestment Partners, L.P.		217,962		0.21	%

On account of the THL Stockholders’ Agreement (as defined and more fully described in Item 6 of the Schedule 13D), the Reporting Persons may be deemed to constitute a “group” (within the meaning of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”).

(c) Other than the Offering, no Reporting Person has entered into any transactions in the securities of the Issuer within the last 60 days.

(d)(e) Not applicable.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

Item 6 of the Schedule 13D is hereby supplemented by adding the following immediately after the final paragraph thereof:

In connection underwritten sale of Syneos Common Stock described in Item 4 of this Amendment No. 1, the Reporting Persons agreed in the underwriting agreement to customary restrictions on sales of securities in a Lock-up Agreement for a specified period of time following the underwritten sale.  The underwriting agreement is filed as Exhibit 99.4 hereto.

Item 7. Material to Be Filed as Exhibits

99.3*	Lock-Up Agreement, dated August 6, 2018, between Morgan Stanley and the THL Funds.
99.4	Underwriting Agreement, dated August 6, 2018, between Morgan Stanley and the THL Selling Stockholders (incorporated by reference to Exhibit 1.1 of the Current Report on Form 8-K filed by Syneos Health, Inc. with the Securities and Exchange Commission on August 8, 2018).

* Filed herewith.

Signature

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: August 13, 2018	THOMAS H. LEE ADVISORS, LLC
	By: THL Holdco, LLC,
	its Managing Member

By:  /s/ Charles P. Holden

Name: Charles P. Holden

Title: Managing Director

Date: August 13, 2018	THOMAS H. LEE EQUITY FUND VI, L.P.
	THOMAS H. LEE PARALLEL FUND VI, L.P.
	THOMAS H. LEE PARALLEL (DT) FUND VI, L.P.
	By: THL Equity Advisors VI, LLC,
	its General Partner
	By: Thomas H. Lee Partners, L.P.,
	its Sole Member
	By: Thomas H. Lee Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member

By:  /s/ Charles P. Holden

Name: Charles P. Holden

Title: Managing Director

Date: August 13, 2018	THL OPERATING PARTNERS, L.P.
	THL COINVESTMENT PARTNERS, L.P.
	THL FUND VII COINVESTMENT PARTNERS, L.P.
	By: Thomas H. Lee Partners, L.P.,
	its General Partner
	By: Thomas H. Lee Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member

By:  /s/ Charles P. Holden

Name: Charles P. Holden

Title: Managing Director

Date: August 13, 2018	GREAT-WEST INVESTORS, L.P.
	By: Thomas H. Lee Advisors, LLC,
	Attorney-in-Fact
	By: THL Holdco, LLC,
	its Managing Member

By:  /s/ Charles P. Holden

Name: Charles P. Holden

Title: Managing Director

Date: August 13, 2018	PUTNAM INVESTMENTS EMPLOYEES’ SECURITIES COMPANY III, LLC
	By: Putnam Investments Holdings, LLC,
	its Managing Member
	By: Putnam Investments, LLC,
	its Managing Member
	By: Thomas H. Lee Advisors, LLC,
	Attorney-in-Fact
	By: THL Holdco, LLC,
	its Managing Member

By:  /s/ Charles P. Holden

Name: Charles P. Holden

Title: Managing Director

Date: August 13, 2018	THL EQUITY FUND VII INVESTORS (INVENTIV), L.P.
	THOMAS H. LEE EQUITY FUND VII, L.P.
	THOMAS H. LEE PARALLEL FUND VII, L.P.
	THOMAS H. LEE PARALLEL (CAYMAN) FUND VII, L.P.
	THL EXECUTIVE FUND VII, L.P.
	By: THL Equity Advisors VII, LLC,
	its General Partner
	By: Thomas H. Lee Partners, L.P.,
	its Sole Member
	By: Thomas H. Lee Advisors, LLC,
	its General Partner
	By: THL Holdco, LLC,
	its Managing Member

By:  /s/ Charles P. Holden

Name: Charles P. Holden

Title: Managing Director

EX-99.3

Exhibit 99.3

Syneos Health, Inc.

Lock-Up Agreement

August 6, 2018

Morgan Stanley & Co. LLC

1585 Broadway

New York, New York 10036

Re: Syneos Health, Inc. - Lock-Up Agreement

Ladies and Gentlemen:

The undersigned understands that you, propose to enter into an Underwriting Agreement (collectively, the “Underwriters”), with Syneos Health, Inc., a Delaware corporation (the “Company”), and the Selling Stockholders named in Schedule II to such agreement providing for a public offering of shares of Class A Common Stock, par value $0.01 (the “Stock”) of the Company (the “Shares”) pursuant to the Registration Statement on Form S-3 (No. 333-208286) filed with the Securities and Exchange Commission (the “SEC”).

In consideration of the agreement by the Underwriters to offer and sell the Shares, and of other good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the undersigned agrees that, during the period specified in the following paragraph (the “Stockholder Lock-Up Period”), the undersigned will not offer, sell, contract to sell, pledge, grant any option to purchase, make any short sale or otherwise dispose of any shares of Stock of the Company, or any options or warrants to purchase any shares of Stock of the Company, or any securities convertible into, exchangeable for or that represent the right to receive shares of Stock of the Company, whether now owned or hereinafter acquired, owned directly by the undersigned (including holding as a custodian) or with respect to which the undersigned has beneficial ownership within the rules and regulations of the SEC (collectively the “Undersigned’s Shares”).  The foregoing restriction is expressly agreed to preclude the undersigned from engaging in any hedging or other transaction which is designed to or which reasonably could be expected to lead to or result in a sale or disposition of the Undersigned’s Shares even if such Shares would be disposed of by someone other than the undersigned.  Such prohibited hedging or other transactions would include without limitation any short sale or any purchase, sale or grant of any right (including without limitation any put or call option) with respect to any of the Undersigned’s Shares or with respect to any security that includes, relates to, or derives any significant part of its value from such Shares.

The Stockholder Lock-Up Period will commence on the date of this Lock-Up Agreement and continue for 30 days after the public offering date set forth on the final prospectus used to sell the Shares pursuant to the Underwriting Agreement.

Notwithstanding the foregoing, the undersigned may transfer the Undersigned’s Shares:

(i) as a bona fide gift or gifts;

(ii) to any beneficiary of the undersigned pursuant to a will, other testamentary document or intestate succession to the legal representatives, heirs, beneficiary or immediate family member of the undersigned;

(iii) to any trust, partnership, limited liability company or other entity for the direct or indirect benefit of the undersigned or the immediate family of the undersigned;

(iv) to any immediate family member or other dependent;

(v) as a distribution to limited partners, members or stockholders of the undersigned;

(vi) to the undersigned’s affiliates or to any investment fund or other entity controlled or managed by the undersigned;

(vii) to a nominee or custodian of a person or entity to whom a disposition or transfer would be permissible under clauses (i) through (vi) above;

(viii) pursuant to an order of a court or regulatory agency or to comply with any regulations related to the Undersigned’s ownership of Shares; provided that in the case of any transfer or distribution pursuant this clause, any filing under Section 16(a) of the Exchange Act, reporting a reduction in beneficial ownership of shares of Stock, shall state that such transfer is pursuant to an order of a court or regulatory agency or to comply with any regulations related to the ownership of the Shares unless such a statement would be prohibited by any applicable law, regulation or order of a court or regulatory agency;

(ix) to the Company or its affiliates upon death, disability or termination of employment, in each case, of the Undersigned;

(x) to the Company or its affiliates (A) deemed to occur upon the cashless exercise of options or (B) for the primary purpose of paying the exercise price of such options or for paying taxes (including estimated taxes) due as a result of the exercise of such options or as a result of the vesting of Stock under restricted stock units or restricted stock awards, in each case pursuant to employee benefit plans disclosed in the Registration Statement; provided that in the case of any transfer or distribution pursuant this clause, except as a result of the vesting of Stock under restricted stock units or restricted stock awards, no filing under Section 16(a) of the Exchange Act (other than a filing on Form 5), reporting a reduction in beneficial ownership of shares of Stock, shall be required or shall be voluntarily made during the Stockholder Lock-Up Period;

(xi) in connection with transactions by any person other than the Company relating to Shares acquired in open market transactions after the completion of the Offering;

(xii) pursuant to a bona fide third party tender offer, merger, consolidation, stock exchange or similar transaction that is approved by the Board of Directors of the Company and made to all holders of the Stock involving a Change of Control (as defined below) of the Company; provided, that if any such tender offer, merger, consolidation, stock exchange or similar transaction is not consummated, such Lock-Up Securities shall remain subject to this agreement; or

(xiii) with the prior written consent of Morgan Stanley & Co. LLC.

providedthat, (1) in the case of each transfer or distribution pursuant to clauses (i) through (vii) above, each donee, trustee, distributee or transferee, as the case may be, agrees to be bound in writing by the restrictions set forth herein, (2) in the case of each transfer or distribution pursuant to clauses (v) through (vii) above, shall not involve a disposition for value and (3) in the case of each transfer or distribution pursuance to clauses (i), (iii) through (vi) and (xi) above, no filing under Section 16(a) of the Exchange Act (other than a filing on Form 5) reporting a reduction in beneficial ownership of shares of Stock, shall be required or shall be voluntarily made during the Lock-Up Period. For purposes of this Lock-Up Agreement, “immediate family” shall mean any relationship by blood, marriage or adoption, not more remote than first cousin.

2

For purposes of this Lock-Up Agreement, “Change of Control” shall mean the transfer (whether by tender offer, merger, consolidation or other similar transaction), in one transaction or a series of related transactions, to a person or group of affiliated persons, of the voting power of the Company’s capital stock if, after such transfer, such person or group of affiliated persons would hold more than 50% of the outstanding voting power of the Company’s capital stock (or of the surviving entity).

In addition, notwithstanding the foregoing, if the undersigned is a corporation, the corporation may transfer the capital stock of the Company to any wholly-owned subsidiary of such corporation; provided, however, that in any such case, it shall be a condition to the transfer that the transferee execute an agreement stating that the transferee is receiving and holding such capital stock subject to the provisions of this Agreement and there shall be no further transfer of such capital stock except in accordance with this Agreement, and provided further that any such transfer shall not involve a disposition for value.  The undersigned now has, and, except as contemplated by clauses (i) through (xiii) above, for the duration of this Lock-Up Agreement will have, good and marketable title to the Undersigned’s Shares, free and clear of all liens, encumbrances, and claims whatsoever.  The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of the Undersigned’s Shares except in compliance with the foregoing restrictions.

The restrictions described in this Lock-Up Agreement shall not apply to: (a) the sale of the Undersigned’s Shares pursuant to the Underwriting Agreement; (b) any transactions effectuated pursuant to a trading plan that satisfies all of the requirements of Rule 10b5-1 under the Exchange Act (“10b5-1 Plan”) existing on the date hereof; or (c) the establishment of a 10b5-1 Plan, provided that no transfers occur under such plan during such Lock-Up Period and no public announcement or filing shall be required or voluntarily made by any person in connection therewith until after the expiration of the Lock-Up Period.

This Lock-Up Agreement shall be terminated and the undersigned shall be released from its obligations hereunder upon the earlier of (i) the date the Registration Statement filed with the SEC with respect to the offering is withdrawn, (ii) the date on which for any reason the Underwriting Agreement is terminated (other than the provisions thereof that survive termination) prior to payment for and delivery of the Shares to be sold thereunder or (iii) August 31, 2018, if the Offering is not completed by such date.

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The undersigned understands that the Company and the Underwriters are relying upon this Lock-Up Agreement in proceeding toward consummation of the offering.  The undersigned further understands that this Lock-Up Agreement is irrevocable and shall be binding upon the undersigned’s heirs, legal representatives, successors, and assigns.

Very truly yours,
THOMAS H. LEE EQUITY FUND VI, L.P.
By:  THL Equity Advisors VI, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THOMAS H. LEE PARALLEL FUND VI, L.P.
By:  THL Equity Advisors VI, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THOMAS H. LEE PARALLEL (DT) FUND VI, L.P.
By:  THL Equity Advisors VI, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

4

GREAT-WEST INVESTORS, LP
By:  Thomas H. Lee Advisors, LLC, its attorney-in-fact
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

PUTNAM INVESTMENTS EMPLOYEES’ SECURITIES COMPANY III, LLC
By:  Putnam Investment Holdings, LLC, its managing member
By:  Putnam Investments, LLC, its managing member
By:  Thomas H. Lee Advisors, LLC, its attorney-in-fact
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THL COINVESTMENT PARTNERS, L.P.
By:  Thomas H. Lee Partners, L.P., its general partner
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THL OPERATING PARTNERS, L.P.
By:  Thomas H. Lee Partners, L.P., its general partner
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

5

THOMAS H. LEE EQUITY FUND VII, L.P.
By:  THL Equity Advisors VII, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THOMAS H. LEE PARALLEL FUND VII, L.P.
By:  THL Equity Advisors VII, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THOMAS H. LEE PARALLEL (CAYMAN) FUND VII, L.P.
By:  THL Equity Advisors VII, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THL EXECUTIVE FUND VII, L.P.
By:  THL Equity Advisors VII, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

6

THL FUND VII COINVESTMENT PARTNERS, L.P.
By:  Thomas H. Lee Partners, L.P., its general partner
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

THL EQUITY FUND VII INVESTORS (INVENTIV), L.P.
By:  THL Equity Advisors VII, LLC, its general partner
By:  Thomas H. Lee Partners, L.P., its sole member
By:  Thomas H. Lee Advisors, LLC, its general partner
By:  THL Holdco, LLC, its managing member
By:	/s/ Charles P. Holden
	Name:  Charles P. Holden
	Title:    Managing Director

7