I've heard that combining antihistamines and alcohol is a bad thing to do. Can you tell me why this is and what effects it has on a person? Also, how long after consuming one should I avoid the other?
A drinker with hayfever
Dear A drinker with hayfever,
Kudos to you for making sure that you aren’t combining substances that could potentially have problematic results! But, before we get into the combination, let’s chat a little about antihistamines. Your body has a lot of mechanisms it uses to keep microbes and foreign elements or pathogens at bay. One of those responses is the histamine mechanism (notorious for many people’s allergy symptoms). When you have an allergic reaction, your body goes into overdrive against what it perceives to be a foreign or threatening element. The runny nose, phlegm, itchy skin, watery eyes, and reduced breathing capacity, are all symptoms of your body reacting to (and trying to reject) the allergen. And what’s the molecule responsible for raising the alarm and triggering this immune response? Yes, you guessed it: histamine.
Antihistamines work by either binding to the receptors on cell surfaces and preventing histamine from binding and triggering an immune response, or they can act to block the production of new histamine molecules in your body. But histamine doesn’t just trigger immune responses: it also has an excitatory effect on the central nervous system. An important thing to note is that there are multiple generations of antihistamines (Generational gaps: they don’t just refer to the differences between us and our parents!). Drugs that are developed around the same time and act similarly mechanistically are also grouped into generations. Regarding antihistamines, there are at least two generations of the drug: First generation antihistamines were developed to block histamine mechanisms broadly, which means first generation antihistamines will stop the itchy, watery eyes, and runny nose, but it will also tend to make you drowsy by depressing the central nervous system. In second generation antihistamines, you get the same benefits of blocking the histamine, but they are less likely to make you as drowsy as first generation.
So, what happens when a person uses alcohol and antihistamines together? First generation antihistamines have been shown to have a pharmacodynamic effect with alcohol. This means that each substance will act as a depressant on the central nervous system, so in combination they can have a significant additive effect (for more information on how alcohol impacts the body, check out the Go Ask Alice! Alcohol archives). When alcohol is used with either first or second generation antihistamines, adverse effects are more likely to occur if the antihistamines are taken in higher than recommended doses. However, if you’re using a second generation antihistamine in the recommended dosage, research has shown that using alcohol at the same time appears to have little or no adverse effect on psychomotor functioning. This seems to be because the second generation antihistamines don’t cross the blood brain barrier the way that the first generation antihistamines (and alcohol) do. Additionally, it’s good to note that how alcohol and/or antihistamines are tolerated and how quickly they are eliminated from the body will vary from person to person. As such, it can be difficult to determine how long to wait to ingest one substance before or after the other.
In deciding whether to drink while on antihistamines, it’s best to consult a pharmacist or your health care provider to talk more about any contraindications of your antihistamine and any other substances or medications you may use. Additionally, s/he may also help you find an antihistamine designed for those who want to avoid sedative effects of the first generation versions.Alice!