Dear Alice,

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?

Thanks,
A drinker with hayfever

Dear A drinker with hayfever,

It's a great idea that you're looking into whether certain substances may have the potential for problematic or undesirable results! To answer your question — it’s best to avoid mixing alcohol and antihistamines, as they both depress the central nervous system (CNS), thereby impairing your ability to coordinate physical motor movements and remain awake and conscious. Additionally, alcohol decreases the efficacy of the antihistamines and can leave you to deal with hay fever’s unpleasant symptoms for a longer period of time. Furthermore, as there are individual differences in how people tolerate and break down each substance — when taken individually or together — it’s difficult to determine how long you may need to wait to consume one after using the other.

To further explore the interplay between alcohol and antihistamines, it might help to talk a bit more about what happens when the body experiences allergies. The body has a lot of mechanisms to fight against microbes, foreign elements, and pathogens. One such response includes its histamine mechanism — notorious for causing allergy symptoms. When someone has an allergic reaction, the 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 the 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. This is where antihistamines come into play.

Generally, there are two key types of antihistamines, which differ based on their ability to induce drowsiness: first generation and second generation antihistamines. First generation antihistamines are commonly labeled as “drowsy”, as they can easily cross the blood-brain barrier, thereby depressing the CNS more readily. Alternatively, second generation antihistamines are commonly labeled “non-drowsy”, as they’re less likely to cross the blood-brain barrier and depress the CNS. But regardless of the generation, antihistamines work in one of two ways. First, some can bind to the receptors on cell surfaces, thereby preventing histamine from binding and triggering an immune response. The other way is to block the production of new histamine molecules in the body. That’s how antihistamines can stop the itchy, watery eyes, and runny nose associated with hay fever and other allergies!

So, what may happen if you mix alcohol and antihistamines together? Well, it’s hard to say for certain, as there are individual differences in how people tolerate and eliminate the combination from their systems. On its own, alcohol depresses the CNS. In combination with a recommended dosage of first generation antihistamines (which also depress the CNS), people are likely to experience an additive effect, making them feel increasingly sedated or sleepy. Moreover, they can experience severely impaired motor skills, dizziness, and a reduction in alertness and awareness. However, if they combine alcohol with a recommended dosage of second generation antihistamines, research indicates that some types may cause them to experience some adverse effects on psychomotor functions, which is when the brain and body work together to complete a task (e.g., driving or catching a ball). But be warned — although research found fewer adverse side effects of second-generation antihistamines and alcohol combined, that doesn't mean it's safe to mix this medicine with alcohol! If you take any antihistamine at higher-than-recommended doses or consume alcohol in a high-risk manner, the adverse effects of combining alcohol and antihistamines are generally heightened for people with the following health conditions:

  • Enlarged prostate
  • Epilepsy
  • Overactive thyroid
  • Heart disease
  • Diabetes
  • Liver problems

Therefore, if you’re deciding whether to drink alcohol while on antihistamines, it’s highly recommended that you speak with a health care provider or pharmacist about the type of antihistamine you’re taking, other substances or medications you may use, and your general health status (especially as it relates to the conditions mentioned above). Additionally, they can point out medications that don't have the sedative effects.

So cheers to treating your ale-ments first and enjoying your drinks after!

Alice!

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