How exactly does alcohol interact with other drugs in the body? It might be tempting to think of each alcohol-drug interaction as a chemical reaction between ethanol and the drug molecules in question. As it turns out, however, this is not often the case. Instead, it is the role of enzymes – which are specialized proteins – in alcohol and drug degradation that causes many of these interactions.

So, if the alcohol doesn’t react with the drugs to prevent their metabolism, then what happens? The answer has to do with the versatility of metabolic enzymes.

Alcohol and drug interactions can be broadly classified in four categories. The first is a result of acute, or momentary, consumption of alcohol. In this situation, the presence of alcohol prevents the metabolism, or chemical breakdown, of drugs; this increases the availability of these drugs in the bloodstream. So, if the alcohol doesn’t react with the drugs to prevent their metabolism, then what happens?

The answer has to do with the versatility of metabolic enzymes. The human body uses the same set of enzymes to metabolize many drugs, including alcohol. However, each enzyme can only metabolize one molecule at a time. If an enzyme is metabolizing ethanol, then it can’t metabolize other drugs until it has finished breaking down the alcohol. As a result, the drug molecules can stay in the bloodstream longer, enhancing the effects of these medications.

An opposite effect stems from chronic, or long-term, use of alcohol. The body becomes accustomed to breaking down large quantities of ethanol and therefore has higher base levels of activated metabolic enzymes. Drugs are broken down at a faster rate, which reduces both their availability and their potency in the body. This is important when prescribing medication to patients with a history of alcohol abuse, who will often need higher doses of these medications to experience the desired effects.

Image from Wikimedia Creative Commons: "AlcoholDehydrogenase-1A4U" by Jag123 at English Wikipedia - Transferred from en.wikipedia to Commons.. Licensed under Public Domain via Commons -

A scientific model of the alcohol dehydrogenase molecule, which breaks down ethanol in the body

These effects of alcohol on drug metabolism go both ways. In particular, the dependence of drug metabolism on enzymes means that the presence of drugs in the body may limit alcohol metabolism in the same way that alcohol can limit drug metabolism. In other words, taking medications may enhance or limit the availability of alcohol, which in turn will modify the direct effects of alcohol on behavior and thought.

Not all alcohol-drug interactions are based on dosage and availability, however. A third category of interactions, according to the National Institutes of Health (NIH), results when enzymes are activated by chronic alcohol consumption and then transform drugs into toxic chemicals. These toxic breakdown products can cause severe damage to the liver and other vital organs, as well as increasing stomach bleeding.

Finally, alcohol can interact with sleep-inducing drugs at their site of action in the brain, which will often magnify their effects. For example, someone who has been drinking may experience severe drowsiness after taking sleeping pills, as the alcohol enhances the effect of the medication.

Many of the effects of alcohol consumption on the human body, from impaired judgement to slurred speech and loss of motor skills, are easy to observe. Alcohol drug interactions, however, can be invisible at first, but once symptoms manifest, the consequences can be severe. According to the NIH, alcohol-drug interactions could be a factor in 25 percent of all emergency room cases. This is not surprising, considering that 70 percent of the adult population reports consuming alcohol, while nearly 50 percent of people report using at least one prescription drug in the past 30 days.

To compound the problem, even medications of the same category will interact with alcohol in different ways. For example, while the availability of the antibiotic Isoniazid is reduced by acute alcohol consumption, the availability of another antibiotic, Rifampin, is reduced by chronic consumption.

Given statistics about the prevalent use of alcohol and prescription medication, it is easy to see why harmful alcohol-drug interactions are common in the United States. And with so many drugs on the market, the number of possibly harmful interactions is endless. This makes it especially important to look up the specific documented interactions between medications and alcohol in order to avoid the negative side effects of each interaction. Armed with a little bit of scientific information, everyone can stay safe while having fun.

About The Author

Sam Garfinkle
Writer and Editor