This is the third post in the series, Alcohol and drug interactions. The other posts are Disulfiram-like Reaction, 2nd Part and 4th Part.
Alcohol increases the risk of sedation, drowsiness and falls, especially in the elderly population and with the 1st gen antihistaminics.
With Barbiturates and Benzodiazepines
Alcohol acts synergistically with them to increase their sedative effects and memory-impairing effects( This memory-impairing effect is misused in Date Rape drug, Flunitrazepam(Rohypnol)). Besides it also inhibits their metabolism in the liver, hence, increasing the drug's levels in the blood.
With H2-Receptor Antagonists
These agents(eg., Cimetidine, Ranitidine) inhibit the action of Alcohol dehydrogenase(ADH) present in gastric mucosa. Cimetidine may also increase the rate of gastric emptying hence increasing the absorption of alcohol. So both of these effects contribute to increasing the Blood Alcohol levels.
With Muscle Relaxants
Several muscle relaxants (e.g., carisoprodol, cyclobenzaprine, and baclofen), when taken with alcohol, may produce a certain narcotic-like reaction that includes extreme weakness,
dizziness, agitation, euphoria, and confusion. For example, carisoprodol is a commonly abused and readily available prescription medication that is sold as a street drug. Its metabolism in the liver generates an anxiety-reducing agent that was previously marketed as a controlled substance (meprobamate). The mixture of carisoprodol with beer is popular among street abusers for creating a quick state of euphoria.