Antabuse is used in the treatment of alcohol dependence, even after the ingestion of a small amount of alcohol it can cause a violent reaction caused by the accumulation of acetalehyde in the body. Reactions include flushing of the face, throbbing headaches, palpitations, tachycardia, nausea and vomiting. With a large enough dose of alcohol Antabuse can cause arrhythmias, hypotension and collapse. These reactions can be triggered by the smallest amount of alcohol present in many over the counter medicines.

Although I have never been prescribed Antabuse, I do know a number of people who have been through alcohol recovery units and taken the drug. It is a terrifying sight to see someone trying to drink even though their body is fighting violently against the drug they so desperately crave, trying to drink faster than the drug can react (and failing) purely because their dependence was so powerful.

Medical details from the British National Formulary (BNF) 37 - March 1999