Coprinopsis atramentaria, commonly known as the alcohol inky cap, common ink cap, tippler's bane, or inky cap, is a species of fungus. It is the second best-known ink cap after Coprinus comatus, its former congener. The grey-brown cap is initially bell-shaped before opening, after which it flattens and disintegrates. The flesh is thin and the taste mild.

It is a widespread and common throughout the Northern Hemisphere. Clumps of mushrooms arise after rain from spring to autumn, commonly in urban and disturbed habitats such as vacant lots and lawns, as well as grassy areas. It can be eaten, but due to the presence of coprine within the mushroom, it is poisonous when consumed with alcohol, as it heightens the body's sensitivity to ethanol in a similar manner to the anti-alcoholism drug disulfiram.

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