Taking multiple drugs simultaneously can lead to unintended and potentially fatal consequences because of how they work in the brain. Drugs can modify neurotransmission by increasing or decreasing the chemical activity. When two drugs work on the same system, their effects can be additive, greatly increasing the risk of overdose. For example, alcohol and barbiturates both bind to GABA receptors. GABA’s inhibitory action has a sedating effect, which is a good thing when you need to relax. But too much GABA will relax physiological processes to the point where unconscious, life-sustaining activities shut down, causing you to stop breathing and die.
Hundreds of deaths are caused annually in the U.S. when drugs like alcohol and barbiturates are taken in combination (Kochanek et al., 2012). In 2009 alone, 519,650 emergency room visits were attributed to use of alcohol in combination with other drugs (SAMHSA, 2010).