Unpleasant
Coprine, the alcohol reaction
Coprine
Onset after the meal
20 minutes to 2 hours after drinking, and the mushroom may have been eaten days earlier
Inside six hours, which is the reassuring side of the line, with one qualification: a mixed wild meal can produce an early reaction that hides a late one.
Attacks
Alcohol metabolism
What it does
Sudden flushing of the face and neck, a pounding heart, throbbing headache, nausea and a powerful sense of impending doom. It is the same mechanism as the drug disulfiram used to treat alcoholism.
How it runs
Passes within a few hours and does lasting harm only in people with heart disease.
Treatment
Supportive. Avoid alcohol entirely for at least three days after eating the mushroom.
The catch
The delay is what makes it strange. The mushroom is harmless alone, and the reaction can be triggered by a drink taken up to about three days later, so people blame the drink and never connect it to a meal from earlier in the week.
Species that cause it
This is reference material, not clinical guidance and not a substitute for a poison centre. If somebody is unwell after eating a wild mushroom, call one now, tell them the interval between the meal and the first symptom, and keep an uncooked specimen.