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Antihistamines and Opioids could prove to be a Dangerous Mix

The CDC has uncovered a stunning new revelation of a drug interaction involving opioids. Although surprising to some, the source of concern comes from over-the-counter or prescription allergy medications containing antihistamines. Autumn is the time of year when allergy sufferers readily reach for their choice of relief from the medicine cabinet, and many powerful types of antihistamines that were once prescription only are now available at the drug store. This is proving to be problematic as 18% of over 92,000 overdose deaths in 43 states between 2019 and 2020 showed toxicology reports containing antihistamines. This situation raises complicated questions as the opioid crisis continues to reach record highs in certain parts of the country and provides yet another challenge for lawmakers and researchers seeking ways to help those suffering.

The OTC Conundrum

Over 71% of overdose deaths between 2019 and 2020 included diphenhydramine, more commonly known by its brand name Benadryl®, which is readily available in drug and grocery stores everywhere in various formulations. While less than .1% (90 deaths) involved antihistamines as the sole cause of death, over 82% of the deaths involved a combination of diphenhydramine and opioids. While this evidence pushes for more warnings about drug interactions, the question remains: why are antihistamines and opioids mixed so often? The answer to this question is complicated and involves many factors.

  • The sedating effects of antihistamines like diphenhydramine can exacerbate respiratory depression caused by opioids. This event is characterized as shallow, decreased breathing, which is the most common cause of death during an overdose.

  • Some people may self-medicate with antihistamines to alleviate the side effects of opioid withdrawal and long-term opioid misuse, such as itching, nausea, insomnia, and many others.

  • Diphenhydramine can be misused on its own and has become popular as a readily available OTC substance that some users claim will produce a hallucinogenic high, despite many warnings to the contrary.

  • Illicit drug manufacturers sometimes use diphenhydramine as a “filler” substance for their product, thus adding an unknown interaction element to unsuspecting users.

  • Naloxone can help reverse the effects of opioid overdose, including respiratory depression, but has no impact on antihistamines, which could prove fatal for those who mix the substances.

  • Despite the misuse of diphenhydramine, it can also provide an accessible life-saving measure, such as stopping an acute allergy and serve as a first-aid tool to help treat common issues like hay fever, the common cold, and the various symptoms related to motion sickness.

Awareness is Key

Although the FDA has taken measures to restrict purchases of similar allergy-relieving medications containing substances like pseudoephedrine, ephedrine, and phenylpropanolamine to limit their uses in manufacturing illicit drugs, it may take a while before diphenhydramine joins the list. For now, the most effective and immediate step is raising awareness of the potentially fatal drug interaction between opioids and diphenhydramine medications to prevent accidental overdose deaths.

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