Why You May Want To Think Twice Before Taking Antihistamines With This Medication

Allergies affect up to 50 million people in the United States, which means many suffer from congestion, fatigue, hives, or nausea as a result (via Cleveland Clinic). When the body encounters a possible threat, the immune system releases histamine, stimulating processes in your stomach, intestines, and circulatory system. That's what causes the allergy symptoms. To block histamine, allergy sufferers might reach for an antihistamine for relief. However, if you're currently taking a monoamine oxidase inhibitor (MAOI), it can boost the effect of the antihistamine, resulting in a dangerous drop in blood pressure (via WebMD).

MAOIs block the monoamine oxidase enzyme. This enzyme clears neurotransmitters such as norepinephrine, serotonin, and dopamine from the brain, according to Mayo Clinic. Because these neurotransmitters contribute to our emotional well-being, MAOIs are prescribed for depression. According to the National Library of Medicine, MAOIs have the potential to be toxic because they can interact with different foods and medications. That's why doctors commonly prescribe newer antidepressants, rather than MAOIs.

These days, MAOIs are prescribed to people when other antidepressants aren't working, according to Drugs.com. They also take weeks to clear your system because the body must make new MAO enzymes. Before starting a different medication that affects neurotransmitters, it's suggested to take at least 14 days for the MAOI to leave the body. Medications like Linezolid, Methylene blue, and some prescriptions to treat Hodgkin's and Parkinson's disease aren't necessarily MAOIs, but they perform the same function in blocking the MAO enzymes. Serotonin syndrome can occur if you take an MAOI with these medications.

According to U.S. Pharmacist, dextromethorphan – which usually treats coughs — can also interact with MAOIs. A 26-year-old woman took twice her dose of phenelzine after missing her earlier dose. She also took dextromethorphan, and the interaction caused a severe fever and a dangerous drop in blood pressure. She died four hours after arriving at the hospital. A 15-year-old girl also died after combining dextromethorphan and MAOIs.

WebMD suggests consulting with your doctor if you experience weakness, dizziness, fainting, or blurred vision while taking antihistamines and MAOIs. You should also consult with your doctor before adjusting any of your medications' dosages.