Cyproheptadine

Overview

Cyproheptadine, sold as Periactin, is arguably the safest and most-effective antihistamine because it also lowers serotonin. Serotonin is a stress mediator involved in everything from bronchial constriction and intestinal hypermotility to migraines, blood vessel inflammation, blood clotting, and osteoporosis. A chemical that blocks both histamine and serotonin can interrupt many distinct disease processes at once. The published literature from the 1940s, 50s, and 60s repeatedly showed cyproheptadine to be useful for allergies, migraines, lymphoma and more, but that body of evidence got buried by the rise of the SSRI industry, which sold the opposite premise. Used at sensible doses, cyproheptadine is one of the better broad-spectrum anti-inflammatory tools available.

Key Points

• Cyproheptadine is both antiserotonin and antihistamine, which is why it covers more ground than typical antihistamines. Most antihistamines only block histamine, but cyproheptadine simultaneously blocks serotonin, which is a more destructive inflammatory mediator. Histamine and serotonin work as parallel acute inflammatory signals, and shutting down both at once produces broader anti-inflammatory effects than either alone. This is the basis for using it in allergy, asthma, gut hypermotility, migraine and post-infection inflammation.

• Cyproheptadine functionally blocks estrogen by being both a strong antihistamine and a powerful anticholinergic. Histamine and the cholinergic system are the two legs on which estrogen stands, so giving cyproheptadine is effectively giving the person an anti-estrogen, even though the drug does not bind directly to the estrogen receptor. Estrogen is severely toxic to the liver in any animal model, causing enlargement when used sporadically and liver cancer when used chronically, even at low doses, so blocking it through cyproheptadine has wide systemic value.

• It works for asthma, bronchitis, and night-time breathing problems by blocking serotonin. Serotonin causes localized contraction of the tubes in the lungs. It also makes them take up water and become inflamed. Ray took Cyproheptadine to relieve nighttime bronchitis and improve breathing during sleep. This fits with the broader picture of asthma as a serotonin and estrogen-driven inflammatory condition rather than a purely allergic one.

• It slows hyperactive bowel function because most of the body's serotonin is made in the gut. About 95% of the body's serotonin is made in the intestine, and any irritation there increases serotonin release, which speeds peristalsis and causes diarrhea. Cyproheptadine, with its antiserotonin and antihistamine action, slows the overactive bowel. Irritable bowel syndrome is described as a chronic overproduction of serotonin in the gut, and anti-serotonin agents address that directly.

• It is one of the recommended interventions for respiratory viral infections including coronavirus, alongside aspirin and Losartan. The main thing during a respiratory infection is to limit inflammation rather than try to kill the virus. The Chinese were recommending Losartan and cinanserin (another antiserotonin agent) for coronavirus, and cyproheptadine fits the same role as a safe, broad-spectrum anti-inflammatory. The recommended sequence was aspirin first, then Losartan and the antiserotonin drugs if aspirin wasn't working.

• Cyproheptadine lowers cortisol and adrenaline production and is an official treatment for Cushing disease in several European countries. Serotonin is the most potent activator of pituitary ACTH release (ACTH is what tells the adrenals to make cortisol). Blocking serotonin shuts this pathway down. In several European countries cyproheptadine is the official treatment for both Cushing's disease and Cushing's syndrome, and also for major depression, which is also characterized by overproduction of cortisol. It has also been used successfully for Nelson syndrome, where the pituitary goes into overdrive after the adrenal glands are removed.

• There is a published case study of cyproheptadine fully curing terminal metastatic liver cancer at 4 mg three times daily. A patient with stage four liver cancer fully metastasized to bone and other organs, who had stopped all chemotherapy and radiation because the doctors said there was no point, was given 4 mg of cyproheptadine three times daily. Within two weeks the primary tumor and most of the metastatic nodules were gone on imaging. The patient stayed on cyproheptadine for a total of 14 months, at which point both the primary tumor and the metastases were fully resolved, and liver function biomarkers stayed normal throughout.

• Cyproheptadine immediately stops withdrawal symptoms from any kind of substance abuse. Almost all withdrawal symptoms, regardless of the substance, are caused by acute elevation of serotonin. Cyproheptadine is one of the most commonly used drugs to treat serotonin syndrome, and it has been shown to immediately stop withdrawal symptoms regardless of the substance involved or the duration of the addiction. It also blocks the histamine surge that opioids cause, which is one of the reasons giving opioids to cancer patients is one of the worst things you can do.

• A 1960s study found a small dose of cyproheptadine was effective against lymphoma. This was part of a body of mid-century research showing cyproheptadine was beneficial for serotonin-related conditions, including a 1975 Polish pharmacology article on cyproheptadine for migraines connected to the gut. That research became inconvenient when the drug industry pivoted to SSRIs, which raise serotonin instead of lowering it, and the older work got buried.

• Cyproheptadine resolves post-surgical delirium and is being studied for schizophrenia and PTSD nightmares. Post-anesthetic delirium is caused by very high serotonin and is symptomatically indistinguishable from a schizophrenia episode, with people hearing and seeing things that are not there. Cyproheptadine, which has activity only on the serotonin receptors, immediately stops the delirium, which is strong evidence that schizophrenia itself is a serotonin issue.

• It is one of the safer anti-serotonin alternatives to ivermectin and other heavily-promoted drugs. Ivermectin would be one of the last things to try given the safer alternatives. Cyproheptadine and famotidine, which is an acid blocker but also apparently a potent anti-serotonin agent, are cheaper, available over the counter in many places, and can do as well or better than ivermectin with fewer side effects.

• Stopping cyproheptadine after a course causes endogenous serotonin production to drop. When you stop cyproheptadine over the next 24 to 48 hours, endogenous serotonin production declines dramatically. The body, having sensed that serotonin appeared plentiful at the receptor level during the course, downregulates the expression of tryptophan hydroxylase, the enzyme that synthesises serotonin. The result after stopping is higher serotonin sensitivity but lower overall serotonin in the body, which is the desirable state, since it is the absolute amount of serotonin that drives chronic disease.

Notable Quotes

"That (cyproheptadine), I think, is the safest antihistamine because it also takes down serotonin excess."

[Ray Peat — KMUD: Language Criticism & Estrogen, June 2017]

"After you've used a few of the typical doses of one or two milligrams, it seems that you get more sensitive to it and can get a good reaction from a tenth of a milligram."

[Ray Peat — KMUD: Language Criticism & Estrogen, June 2017]

"My first experiences with cyproheptadine were to improve my breathing at night, and over the first two or three nights I was getting a good sleep because of the relieved bronchitis, but after about five nights I started having weirdly intense dreams. I think it was the changing balance of serotonin and histamine... When I returned to taking it, I found that I had become about ten times more sensitive to it (needed a dose 10 times smaller)"

[Ray Peat — In Defense of Mexican Coke, The Authoritarian Metabolism, Symbols of an Alien Sky, Astrology]

"One study found that a small dose of cyproheptadine was effective against lymphoma."

[KMUD host quoting study, Ray Peat confirming — KMUD: Evidence-Based Medicine, September 2018]

"I have to say I tried cyproheptadine and it is the most relaxed I may have ever felt in my whole life. It's like a really potent anti-anxiety medication."

[Georgi Dinkov — Georgi Dinkov on Serotonin: Happiness or Stress Chemical?]

Important Things To Consider

Sensitivity builds rapidly, and full tablets can become too much within days. Starting at 1 to 2 milligrams is reasonable, but after a few days the same dose may produce stronger effects than wanted. The practical approach is to drop to a small fraction, around a tenth of a milligram, once the system has adapted. Continuing at the standard 4 mg tablet can produce excessive sedation and other unwanted effects.

Cyproheptadine is sedating and impairs sleep quality. It will put you to sleep so it's recommended to cut a 4mg tablet into a half, quarter or even an eighth (0.5mg) to avoid drowsiness. It can take around a week to get over the drowsiness.

Published case reports exist of cyproheptadine elevating liver enzymes. Some published case studies show elevated liver enzymes in patients on cyproheptadine. In the 14-month liver cancer case, however, liver biomarkers stayed normal throughout, which is significant given that the patient was specifically being treated for liver cancer. The risk exists but appears not to be universal.

The sedation side effect is specifically due to histamine blockade, not serotonin antagonism. Cinanserin, which has a similar serotonin antagonist profile to cyproheptadine but no activity on histamine receptors, has a calming effect without the same drowsiness. Serotonin antagonists in general make people relaxed and sometimes sleepy but not drowsy in the way antihistamines do. People who want the anti-serotonin effects without the sedation may prefer a more histamine-sparing option.

The drug industry actively buried the older antiserotonin literature in favor of SSRIs. Cyproheptadine has been off-patent for decades, so there is no commercial pressure to promote it, while SSRIs that do roughly the opposite (raising serotonin) became the standard of care. This means doctors are generally unfamiliar with cyproheptadine's broader uses, and patients seeking it for off-label indications like migraine, gut motility, or post-viral inflammation may have to navigate that gap themselves.

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