Periactin: What It Is, How It Works, and When It's Used

Periactin is the brand name for cyproheptadine, an antihistamine that’s been around since the 1960s. It’s not a drug you’ll see advertised on TV, but it’s prescribed for specific, sometimes unusual, medical needs. Unlike common allergy pills that just make you sleepy, Periactin has a mix of effects that make it useful in ways most people don’t expect.

How Periactin Actually Works

Periactin blocks histamine, the chemical your body releases during allergic reactions. That’s why it helps with sneezing, runny nose, and itchy eyes. But it also blocks serotonin and acetylcholine - two other brain chemicals. That’s where its other uses come from.

Blocking serotonin can reduce appetite suppression in some people. That’s why doctors sometimes prescribe it to help kids with poor appetite gain weight. It’s not a magic weight-gain pill. It works best when there’s a medical reason for low intake - like after chemotherapy, in kids with failure to thrive, or in people recovering from illness.

It’s also used for chronic hives that don’t respond to regular antihistamines. In some cases, it’s prescribed off-label for migraine prevention, especially in children. The serotonin-blocking effect is thought to calm overactive nerve pathways involved in headaches.

Who Gets Prescribed Periactin?

Most people who take Periactin fall into three groups:

• Children with poor appetite or failure to thrive
• Adults or teens with severe allergic reactions not controlled by other meds
• Patients with serotonin-related conditions like carcinoid syndrome or serotonin syndrome (as part of emergency treatment)

In Australia, it’s not a first-line treatment. Doctors usually try safer, newer antihistamines first. Periactin comes in when those don’t work - or when appetite stimulation is needed. It’s not approved for weight gain in healthy people. Using it for cosmetic reasons is dangerous and not recommended.

Dosing and How to Take It

Periactin comes as tablets or liquid. The dose depends on age, weight, and why it’s being used.

For children with poor appetite, doses usually start at 0.2 mg per kilogram of body weight per day, split into two or three doses. That’s about 2-4 mg total for a small child. The maximum daily dose is typically 12 mg for kids under 15, and 32 mg for adults.

It’s taken with food to reduce stomach upset. Because it causes drowsiness, many people take it at night. Don’t drive or operate heavy machinery until you know how it affects you. Alcohol makes the drowsiness worse.

It takes a few days to see results for appetite. For allergies, relief can come within an hour. For migraines, it may take weeks of daily use before you notice fewer headaches.

Side Effects You Should Know

Periactin isn’t a gentle drug. Its side effects are common and sometimes serious.

• Drowsiness - happens in up to 70% of users
• Dry mouth - very common, can lead to dental issues if not managed
• Constipation - due to its anticholinergic effect
• Blurred vision - especially in older adults
• Increased appetite - intentional in some cases, risky in others
• Restlessness or confusion - more common in elderly patients
• Fast heartbeat or low blood pressure - rare but dangerous

Overdose can cause seizures, hallucinations, and coma. Never take more than prescribed. If someone takes too much, call emergency services immediately.

Who Should Avoid Periactin

Periactin isn’t safe for everyone. You should not take it if you:

• Have glaucoma - it can raise eye pressure
• Have trouble urinating due to an enlarged prostate
• Have asthma or other breathing problems - it can thicken mucus
• Are allergic to cyproheptadine or similar antihistamines
• Are taking MAO inhibitors (like phenelzine or selegiline) - this combination can cause life-threatening reactions
• Are under two years old - safety hasn’t been established

Older adults are more sensitive to its side effects. Falls, confusion, and urinary retention are common risks. Many doctors avoid prescribing it to people over 65 unless absolutely necessary.

Interactions With Other Drugs

Periactin interacts with many common medications. Always tell your doctor or pharmacist what else you’re taking.

• Other sedatives - alcohol, benzodiazepines, sleeping pills - make drowsiness worse
• Antidepressants - especially SSRIs and SNRIs - increase risk of serotonin syndrome
• Anticholinergics - like some bladder or Parkinson’s meds - can cause severe dry mouth, constipation, or confusion
• Stimulants - like ADHD meds - may be less effective because Periactin can counteract them

There’s no safe way to guess these interactions. Even over-the-counter cold medicines often contain antihistamines. Taking Periactin with those can lead to overdose.

Is Periactin Right for You?

Periactin isn’t a drug you pick off the shelf. It’s a tool for specific problems. If you’re considering it for appetite, ask: Is there a medical reason for low intake? Are other options tried? Is the risk of drowsiness or confusion worth the benefit?

If you’re using it for allergies, ask: Have I tried second-generation antihistamines like loratadine or cetirizine? They’re safer, non-sedating, and just as effective for most people.

If you’re using it for migraines, ask: Has my doctor ruled out other triggers like sleep, stress, or diet? Periactin isn’t a first-line migraine treatment in adults - it’s mostly used in kids when other options fail.

There’s no shame in using Periactin if it’s the right tool. But it’s not a cure-all. It’s a medication with clear limits and real risks.

Where to Get It and What It Costs

Periactin is available by prescription only in Australia. It’s listed on the Pharmaceutical Benefits Scheme (PBS), so if you have a Medicare card, you pay the subsidized price - around $30 for a 30-day supply. Without PBS, it can cost over $100.

Generic cyproheptadine is also available and just as effective. Many pharmacies will switch you to the generic unless your doctor specifies the brand. The generic works the same way and costs less.

Don’t buy Periactin online from overseas pharmacies. Many sites sell counterfeit or contaminated versions. The Therapeutic Goods Administration (TGA) warns against importing unapproved medicines.

What to Do If You Miss a Dose

If you forget a dose, take it as soon as you remember - unless it’s close to your next dose. Then skip the missed one. Never double up to make up for it.

Stopping Periactin suddenly isn’t dangerous, but if you’ve been using it for migraines or appetite, symptoms may return. Talk to your doctor before stopping, especially if you’ve been on it for more than a few weeks.

Alternatives to Periactin

Depending on your reason for taking it, there are often safer or more modern options.

For allergies: Loratadine (Claritin), cetirizine (Zyrtec), or fexofenadine (Telfast) are non-sedating and just as effective. No drowsiness, no weight gain, no dry mouth.

For appetite stimulation: Megestrol acetate (Megace) is sometimes used in adults with cancer-related appetite loss. But it has its own risks, like blood clots. For kids, nutritional counseling and high-calorie supplements often work better than drugs.

For migraines: Topiramate, amitriptyline, or propranolol are preferred for adults. In children, cyproheptadine is still used, but newer options like riboflavin or magnesium are being studied.

Periactin has a place - but only when other options don’t fit.