Why Are So Many Women Mixing Allergy Meds With Pepcid AC?

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Before perimenopause, Angela hiked over 100 miles a month. “I was incredibly active,” she told me. “I moved to the mountains so I could hike,” she tells me. Then: “Man, oh man,” she says with a sigh. “Perimenopause wiped me out.”

With approval from her doctor, Angela began taking HRT, or hormone replacement therapy, for her symptoms, but it didn’t make a big enough dent. She was still fatigued and worse, almost completely uninterested in her former hobbies, hiking included. Then, a few months ago, Angela saw a social-media post from a woman who took daily antihistamines (like Allegra, Claritin, or Zyrtec) plus Pepcid AC (a common antacid) for her perimenopause symptoms. Her results, as reported, sounded miraculous: no more brain fog. No more tossing and turning all night. Even her mood vastly improved.

Angela, who is now 55, decided to try the regimen for herself. A former neuroscientist turned data scientist, she was better equipped than most to understand why these ordinary, over-the-counter medications might work to reduce peri- and menopausal symptoms; she knew that hormonal changes can trigger inflammation in the body, which antihistamines can help reduce. (Allergy medications like Allegra and Zyrtec block histamine at H1 receptors, while Pepcid AC is a histamine-2 blocker.) Angela has since shared her own experiences — and related research — on Threads, where a number of users’ posts about taking these drugs have gone viral in recent weeks.

While the most recent online chatter around antihistamines is predominantly connected to treating perimenopause or PMDD symptoms (which can overlap), these medications have also found favor among people affected by a number of chronic, difficult-to-diagnose illnesses, including mast cell activation syndrome (MCAS), long COVID, and post-orthostatic tachycardia syndrome (POTS).

Zachary Rubin, an allergist and clinical immunologist, has seen patients who take antihistamines for these purposes for years.

“Women will go to their doctors and say, ‘I take Allegra and Pepcid and my PMDD symptoms go away. It’s like magic,’” he told me over the phone from his office outside Chicago. He says he’s been getting more questions about this OTC cocktail after his recent interview about it with OB/GYN and menopause expert Mary Claire Haver on her Substack. So far, Rubin says, these experiences are clinically unsupported. “When you look at the literature, there are no clinical trials that actually validate and verify that information,” he says — however, he notes, that does not mean it’s not working for anyone, and there are plausible reasons for why it might work.

“There are some studies that suggest that there is dysregulation of the chemical histamine during the luteal phase of the menstrual cycle, which also often corresponds with the symptoms that women report from PMDD,” Rubin says. Histamine also plays a role in the sleep-wake cycle, mood, digestion, and pain signaling, and many of these systems are dysregulated during hormonal changes. For these reasons, he adds, it “makes sense mechanistically” that these medications might provide relief for PMDD and perimenopause symptoms.

Lisa Mosconi, a neuroscientist and author of The Menopause Brain, agrees. “Biologically, it’s plausible because ovarian-hormone fluctuations can influence immune activity and mast-cell signaling,” she says. (Mast cells are often described as the body’s “alarm system” and, when overprotective, can cause unnecessary activation, as is thought to be the case with MCAS.) This antihistamine “blockade” might help dampen that signaling, Mosconi says.

For Henry, a 30-year-old writer, these drugs have provided enormous relief. After a COVID infection became long COVID, and later POTS, most doctors he saw told him his symptoms were caused by his being overweight. “For a year I had no idea what was going on with me, but I just felt so strange and bad,” he tells me. Henry, who is transmasculine, also experiences severe PMDD and decided to start taking Pepcid AC for PMS after seeing it recommended on TikTok. It seemed to alleviate his mood swings and brain fog almost instantly.

Henry brought his findings to his new psychiatric nurse practitioner, whom he says is more versed in chronic illness and mental health. He also asked her if he could start taking daily Allegra for allergies; she told him she recommended it, having heard Allegra in combination with Pepcid was helpful for people with long COVID and POTS. He’s taken both for a year: Allegra daily and Pepcid for the ten or so days leading up to his cycle. (“I don’t want to be taking Pepcid every day, because I don’t know what the long-term effects are,” he explains.) Since starting the regimen, he says his symptoms — brain fog, malaise, reduced executive functioning — have improved enormously.

Sibyl, a 49-year-old consultant, has also been taking daily Zyrtec and Pepcid for a few weeks after reading about it online. For her, it’s helped enormously with joint pain — a perimenopause symptom exacerbated by her lifelong hypermobility. Though she’s in frequent physical therapy, and takes prescribed Celebrex for pain, she’s found “overnight relief” with these antihistamines. “I took it one night, and I was shocked when I woke up the next day,” she says. Her relief might have something to do with how well she slept, she says — Zyrtec can cause drowsiness, and since taking it, Sibyl says she’s sleeping through the night for the first time in a long time.

When Sibyl brought up her results with her physical therapist and then her OB/GYN, they were supportive. Next, she plans to consult her allergist. “I’m gonna get a group consensus on this, but I’m still taking it because it’s working,” she says. For her, the medications have come with additional, and unexpected, benefits. “I have tinnitus, where one of your ears rings all the time — I got it from a really bad ear infection ten years ago,” she says. “It’s super-weird, but this is the only thing I’ve ever done that turns the volume way down.”

Among those using antihistamines for off-label conditions, there is substantial variation in routine — which is part of the reason a clinical trial would be helpful, Rubin says. “We haven’t had clinical trials to understand the proper dosage,” he explains. “How effective is it? Is there a placebo effect involved or not? What is the overall safety?” Rubin notes that while Pepcid AC and antihistamines like Allegra or Zyrtec are sold over the counter, and therefore considered very safe, they aren’t entirely without associated risk.

“Allegra is generally safer, but you can have weight gain and itching that can occur if you stop the medication too quickly,” he adds. “For Pepcid, while it’s rare to have long-term concerns, there could be issues related to absorption of nutrients like vitamin B-12, magnesium, and calcium.” People with kidney disease need to be particularly careful with long-term Pepcid use, he adds, as it can exacerbate side effects.

Mosconi, the neuroscientist, warns that anyone interested in adopting this regimen should consult their clinician, especially if taking them for off-label uses having to do with mood and cognition. Rubin agrees. “I don’t want to miss something that is underlying that could be explaining these symptoms,” he says. “We don’t want to leave any stones unturned.” For perimenopause, says Mosconi, “There are more evidence-based options.”

Still, she’s sympathetic to patients’ frustration with insufficient research and treatment options. “Women’s midlife health has been chronically underfunded, and these are inexpensive generic [medicines] with little commercial incentive to sponsor large trials,” she explains. “Add in the complexity of studying cyclical symptoms and heterogeneous presentations, and you get a gap where anecdotes spread faster than the science, despite the fact that this is exactly the kind of question we should be testing rigorously.”

Rubin hopes that renewed online attention to these medications’ off-label potential might result in more research but doesn’t seem especially optimistic: As health care becomes more corporatized, and public trust in health-care systems declines, people are bound to seek alternatives. “Most adults will search for health information online,” Rubin says. “One of the powerful tools that social media has is storytelling and people sharing their lived experiences.”

Sibyl says she’s been surprised by the intensity of the response to her post on Threads, but it’s obvious the underlying frustration is resonant. “I saw someone else say that it feels like every woman over 35 is doing a drug trial in their living room, and that’s what’s happening,” she says. “ ‘Lose weight, you’re fat and anxious’ is the answer to everything at a doctor’s office, no matter where you go. We all get dismissed.”

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