X0306 4 2021-05-10 0 0001492426 Horizon Therapeutics Public Ltd Co HZNP 0001529409 Daniel William F C/O HORIZON THERAPEUTICS PLC CONNAUGHT HOUSE, 1ST FL, 1 BURLINGTON RD DUBLIN L2 4 IRELAND 1 0 0 0 Common Stock 2021-05-10 4 M 0 20000 12.70 A 20000 D Common Stock 2021-05-10 4 S 0 19834 86.56 D 166 D Common Stock 2021-05-10 4 S 0 166 87.01 D 0 D Common Stock 74467 I By Trust Stock Option (Right to Buy) 12.70 2021-05-10 4 M 0 20000 0.00 A 2024-09-18 Ordinary Shares 20000 13286 D The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $86.00 to $87.00 per share, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The stock option vested in 36 equal monthly installments following the date of grant. /s/ Miles McHugh, Attorney-in-Fact 2021-05-12