Net Loss Per Common Share (Tables)

6 Months Ended

Jun. 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 June 30,						Six months ended June 30,
(in thousands, except per share amount)	2012			2013			2012			2013
Net Loss Per Share:
Numerator:
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$	(20,026	)	$	(30,082	)	$	(43,310	)	$	(58,235	)
Plus: Unaccreted dividends on convertible preferred stock	(67		)	—			(2,107		)	—
Net loss available to common stockholders—basic and diluted	(20,093		)	(30,082		)	(45,417		)	(58,235		)
Denominator:
Weighted-average common shares—basic and diluted	90,581			96,170			51,214			96,025
Net loss per share available to common stockholders—basic and diluted	$	(0.22	)	$	(0.31	)	$	(0.89	)	$	(0.61	)

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

	As of June 30,
(in thousands)	2012	2013
Options to purchase common stock	17,455	20,447
Common stock warrants	2,905	2,777