Mefenamic Acid - what happens if you mix it with alcohol?

There is a moderate drug-drug interaction when you take mefenamic acid with alcohol.

Generally avoid: The concurrent use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) and ethanol may lead to gastrointestinal side effects, heartburn, ulceration, etc. The mechanism may be due to a combined local effect as well as inhibition of prostaglandins leading to decreased integrity of the GI lining.

Patients should refrain from alcohol consumption while taking aspirin or NSAIDs.

http://www.drugs.com/drug_interactions.php