This viewer asks, does alcohol make antibiotics less effective or interact with them? Some antibiotics and alcohol may have similar side effects such as dizziness, or drowsiness and stomach upset. Taking them together may make these side effects more pronounced. There are also some antibiotics such as Metronidazole, the generic for Flagyl and Trimethaprim-sulfamethoxazole which is the generic for Bactrim and Septra that should not be mixed with alcohol since this may cause a more severe reaction which may include facial flushing, increased heart rate, sweating, headache, nausea and vomiting. A medication to treat tuberculosis Isonyacid may be eliminated from the body more quickly in individuals who are chronic heavy alcohol users. This could lead to a decreased effectiveness of the drug. So always check with your pharmacist or doctor to determine if your medications do interact with alcohol.