Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Taxes

Schedule of tax effects of temporary differences that give rise to significant portions of deferred tax assets

	December 31,
	2023		2022
Deferred tax assets:
Net operating loss carryforwards	$	88,279	$	87,216
Research credit carryforward		7,026		7,071
Capitalized research and development expenses		164		205
Stock options and other		5,028		2,092
Total gross deferred tax assets		100,497		96,584
Valuation allowance for deferred tax assets		(100,497)		(96,584)
Net deferred tax assets	$	—	$	—

Schedule of reconciliation of U.S. statutory income tax rate to effective tax rate

	December 31,
	2023		2022		2021
Federal income tax at statutory rate	21.0	%	21.0	%	21.0	%
State income tax benefit, net of federal benefit	0.9	%	0.1	%	0.2	%
Unrealized gain on warrants	9.8	%	17.8	%	1.1	%
Research and development tax credits	—	%	0.1	%	0.2	%
Other	(4.6)	%	(5.5)	%	(2.2)	%
Increase to valuation allowance	(27.1)	%	(18.0)	%	(20.3)	%
Effective income tax rate	0.0	%	15.5	%	0.0	%