If I'm taking isoniazid can I drink alcohol?

Yes in moderation. Isoniazid can irritate the liver, especially if you are older (more than 50ish). Alcohol can do this too and the results may be additive. It is very important to take all Isoniazid as directed by your doctor. Occasional alcohol should not make a difference. Generally it is routine for your doctor to do blood tests on your liver every 2 or 3 months during the course of your isonizid therapy.