Net Loss Per Common Share (Tables)

9 Months Ended

Sep. 30, 2013

Net Loss Per Common Share

Schedule of computation of basic and diluted net loss per share available to common stockholders

	Three months ended September 30,						Nine months ended September 30,
(in thousands, except per share amount)	2012			2013			2012			2013
Net Loss Per Share:
Numerator:
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$	(23,199	)	$	(39,631	)	$	(66,509	)	$	(97,866	)
Plus: Unaccreted dividends on convertible preferred stock	—			—			(2,107		)	—
Net loss available to common stockholders—basic and diluted	(23,199		)	(39,631		)	(68,616		)	(97,866		)
Denominator:
Weighted-average common shares—basic and diluted	93,724			101,155			65,487			97,754
Net loss per share available to common stockholders—basic and diluted	$	(0.25	)	$	(0.39	)	$	(1.05	)	$	(1.00	)

Schedule of potentially dilutive securities excluded from computation of diluted weighted average shares

	As of September 30,
(in thousands)	2012	2013
Options to purchase common stock	19,812	20,355
Common stock warrants	2,891	2,777
Conversion premium on the Notes	—	25,000