Side effects of drinking alcohol when taking metronidazole include stomach cramping, nausea, flushed skin and headache, according to RxList. Metronidazole should not be given to alcoholics who are taking the medication disulfiram, as the combination of the medications and alcohol can cause psychotic reactions.
Severe side effects of mixing alcohol and metronidazole include increased heart rate, liver damage and blood pressure issues, according to Healthline. Consuming alcohol within 24 hours of taking the medication can increase the risk of side effects. Metronidazole can also cause uncomfortable side effects such as diarrhea, off-colored urine, hand tingling and mouth dryness when combined with alcohol.