Alcohol 12-24h before increases narcosis risk. Antihistamines and anxiolytics have additive sedative effect under pressure.
The question of whether to take aspirin, ibuprofen, or other anti-inflammatory drugs before or after diving is a recurring one. Also discussed are alcohol consumption on the dive boat, anti-seasickness patches or pills, and the use of medications that affect circulation under pressure. Divers seek clear rules that their general practitioners rarely know with sufficient precision.
Alcohol consumption within the 24 hours preceding a dive increases the risk of narcosis and reduces response capacity; experts recommend total abstinence for at least 12–24 hours beforehand. First-generation antihistamines, benzodiazepine anxiolytics, muscle relaxants, and certain antiemetics have an additive sedative effect with narcosis. The Merck Manual warns that any substance that alters consciousness or judgment should be considered contraindicated for divers. Cases of symptomatic narcosis at less than 30 meters have been documented in people who had taken seasickness pills or sleeping aids before the dive.