Can alcohol lower the effects of the antibiotic?

Depends on the med. Doxycycline is less effective with chronic alcohol use. Rifampin and Isoniazid can be more toxic to the liver combined with alcohol. There likely are more interactions; these should be included in the drug information sheet that accompanies the antibiotic. If in doubt, avoid alcohol. If heavy drinker, may need to ask doctor for advice regarding cutting down; stopping suddenly can be dangerous.