Periactin (Cyproheptadine): Uses, Dosage, Side Effects, and Weight Gain Guide

TL;DR / Key takeaways

• Allergy antihistamine that often causes drowsiness and can increase appetite. In the U.S., it’s prescription-only.
• Typical adult dose: 4 mg, 3 times daily (max 20 mg/day; some cases up to 32 mg/day). Kids: weight/age-based-see chart below and check with your clinician.
• Common side effects: sleepiness, dry mouth, constipation, blurred vision, weight gain. Avoid alcohol and other sedatives.
• Not for children under 2, breastfeeding, or people with narrow-angle glaucoma, urinary retention, or on MAOIs.
• Used off-label for appetite/weight gain and pediatric migraine prevention-evidence is modest; use only with medical supervision.

If you’re searching for Periactin, you probably want quick answers: What does it do, is it right for me (or my kid), how much to take, and what pitfalls to avoid. I’ve been that parent trying to decode labels while juggling soccer pick-up for Everly and Linden. This guide trims the noise and gives you practical, safe steps to act on today.

What Periactin Is, How It Works, and Who It Helps

Periactin is the brand name for cyproheptadine, a first-generation antihistamine. It blocks H1 histamine receptors to calm allergy symptoms (itching, watery eyes, sneezing, hives). Unlike newer “non-drowsy” options, it also strongly blocks serotonin and has anticholinergic effects. That mix explains two big things people notice: drowsiness and increased appetite.

What it’s used for (on-label and off-label):

• Allergic conditions: seasonal allergies, allergic rhinitis, itchy skin, hives.
• Off-label: appetite stimulation/weight gain under medical supervision; pediatric migraine prevention; part of hospital treatment for serotonin syndrome (not a do-it-yourself use).

What forms it comes in: tablets (commonly 4 mg) and syrup (often 2 mg per 5 mL). Your pharmacy may stock generic cyproheptadine more than the brand name.

Who it may help: people with stubborn nighttime itching, hives that are worse at night, or those who need an appetite boost under a doctor’s plan. Who it’s not great for: anyone who must stay alert (drivers, machine operators), or people who do fine on non-drowsy antihistamines (loratadine, cetirizine, fexofenadine).

Important safety flags (from U.S. FDA labeling and standard pharmacology texts):

• Age: do not use in infants/children under 2 years; higher risk of serious side effects.
• Medical conditions: avoid with narrow-angle glaucoma, peptic ulcer with obstruction, pyloroduodenal obstruction, bladder neck obstruction, symptomatic enlarged prostate, or severe asthma with thick secretions.
• Medications: do not combine with MAO inhibitors (e.g., phenelzine, tranylcypromine). Use caution with other sedating drugs (benzodiazepines, opioids) and alcohol.
• Breastfeeding: generally not recommended-can sedate the infant. Pregnancy: limited data; talk with your OB first.

Quick reality check: this is a strong, older antihistamine. It can be exactly the right tool when you need sedation and itch relief at night. It’s the wrong tool if you need to be sharp for a 7 a.m. commute.

Dosing: How to Take It Safely (Adults and Kids)

Always follow your doctor’s instructions. The ranges below come from standard dosing found on U.S. FDA prescribing information and pediatric references. Start low, go slow-especially if daytime drowsiness is a problem.

Adults (allergies/itching):

• Usual: 4 mg three times daily with food if needed.
• Range: 4-20 mg/day. Some people may require up to 32 mg/day, divided.
• Tip: If you only need nighttime itch control, try a single evening dose first.

Children (allergies/itching):

• Under 2 years: do not use.
• 2-6 years: commonly 2 mg two to three times daily. Max 12 mg/day.
• 7-14 years: commonly 4 mg two to three times daily. Max 16 mg/day.
• Weight-based guide many clinicians use: about 0.25 mg/kg/day divided into 2-3 doses (do not exceed age-based max).

Off-label dosing notes (doctor-directed only):

• Appetite/weight gain: clinicians often start at low bedtime doses to limit daytime sleepiness, then adjust weekly if needed.
• Pediatric migraine prevention: often bedtime dosing based on weight; the goal is fewer headaches with tolerable sleepiness. Evidence is modest; benefits vary.

When to take it: Food can reduce stomach upset. If drowsy, shift more of the total daily dose to the evening. Avoid alcohol. If you miss a dose, take it when you remember unless it’s near the next one-don’t double up.

Storage and handling: room temperature (68-77°F/20-25°C), away from moisture and light. Keep out of reach of kids-tablets look deceptively harmless.

Side Effects, Interactions, and Red Flags

Common and usually mild:

• Drowsiness or fatigue
• Dry mouth, constipation
• Blurred vision, dizziness
• Increased appetite and weight gain

Less common but important:

• Confusion or agitation (more likely in older adults)
• Urinary retention, especially if you already have trouble peeing
• Worsening of narrow-angle glaucoma
• Thickened bronchial secretions-can be an issue in asthma

Serious-get urgent help:

• Severe drowsiness you can’t stay awake from, fainting, or trouble breathing
• Seizures, hallucinations
• Allergic reaction to the medication (rash, swelling, wheezing)

Interactions to watch (FDA label and standard drug references):

• MAO inhibitors: do not combine (can dangerously boost anticholinergic and sedative effects).
• Alcohol, benzodiazepines, sleep meds, opioids: additive sedation-avoid or use extreme caution.
• Other anticholinergics (e.g., some bladder meds, tricyclic antidepressants): higher risk of dry mouth, constipation, blurry vision, urinary retention.
• SSRIs/SNRIs: no classic dangerous interaction, but be mindful if a doctor is evaluating you for serotonin-related symptoms. Don’t self-treat suspected serotonin syndrome.

Driving and school: If you’re new to this med, don’t drive for at least 24 hours after the first dose. For kids, a bedtime-only plan can reduce daytime fog at school. If a teacher says your child seems zoned out, bring that feedback to the prescriber-it’s a dosing signal.

Weight gain: This is both a side effect and, for some, the goal. Expect appetite to increase within days, weight changes within weeks. If you’re not trying to gain weight, keep an eye on snacks, and take most of the dose at night if possible.

Periactin for Appetite and Migraines: What the Evidence Really Says

Appetite/weight gain: Cyproheptadine’s serotonin-blocking effect can make food more appealing and reduce early satiety. The FDA label lists increased appetite and weight gain as common. In clinical practice, many pediatricians and gastroenterologists use it short-term for underweight kids who struggle with appetite. Studies show modest average weight gain over several weeks, with bigger responses in kids who are truly appetite-limited-less so if nutrition issues are mainly behavioral or due to another untreated condition (like untreated reflux or constipation). The trade-off is sleepiness and sometimes irritability.

Practical expectations for families:

• Timeframe: appetite often picks up within 3-7 days; weight changes show over 2-8 weeks.
• Dosing trick: a larger bedtime dose can improve morning appetite carryover without wrecking daytime focus.
• Stop rules: if there’s no meaningful weight gain after 4-8 weeks, or side effects are too much, rethink the plan with your clinician.
• Pair it with calories that count: smoothies with nut butter, whole-milk yogurt, avocado toast-so the extra appetite feeds growth, not just empty snacks.

Pediatric migraine prevention: Many pediatric neurologists consider cyproheptadine for younger kids because it’s available as a syrup and tends to make sleep easier. The evidence base is modest (small trials and case series). When it works, parents notice fewer headaches and better sleep within a few weeks. When it doesn’t, the main clue is persistent headaches with annoying grogginess-time to switch to another preventive option.

Serotonin syndrome (hospital use): Toxicologists use cyproheptadine because it blocks serotonin receptors. This is managed in hospitals with close monitoring. If you’re reading this because you’re worried about serotonin syndrome, stop and call emergency services. This is not a home problem.

Sources and standards behind these uses: FDA prescribing information for cyproheptadine (latest label updates continue to warn about sedation and anticholinergic effects); pediatric references and neurology guidelines acknowledge off-label migraine prevention with limited evidence; gastroenterology and nutrition clinics commonly use it for appetite with short, supervised trials. Ask your clinician which goal-itch relief, appetite, or migraine prevention-matters most, because dosing and timing shift by goal.

Checklists, Comparisons, FAQ, and Your Next Steps

Quick decision checklist

• Primary goal is nighttime itch or hives? Good fit-start with evening dosing.
• Need daytime allergy control without drowsiness? Consider non-drowsy antihistamines first (loratadine, fexofenadine, cetirizine).
• Trying to boost appetite/weight? Only with a clinician’s plan and a nutrition strategy.
• Under 2 years old, breastfeeding, or have glaucoma/urinary retention/MAOI use? This is a no-go.
• Driving for work or operating machinery? Avoid or keep doses strictly at night.

Periactin vs other antihistamines (what to expect)

Pro tips (from real life and clinic)

• Start on a Friday night. You’ll see how sleepy it makes you without ruining a workday.
• Split doses unevenly-small in the morning, larger at bedtime-to reduce daytime fog.
• For kids, ask the teacher for quick feedback after the first week (focus, mood, appetite at lunch). Adjust with your clinician.
• If appetite surges, prep calorie-dense, nutrient-dense snacks ahead of time so gains are healthy, not just sugary.
• Hydrate and add fiber (fruit, veggies, oats) to counter constipation.

Mini-FAQ

• Is it safe to use daily? Many people use it daily for short periods. Long-term use should be reviewed regularly due to sedation, anticholinergic effects, and weight gain.
• Can I combine it with melatonin? Both can make you sleepy. If your doctor says it’s okay, start low and avoid other sedatives.
• Does it help eczema? It can help with nighttime itch and scratching-less scratching often means fewer flares. It doesn’t treat the skin inflammation itself-keep using your moisturizer and prescribed creams.
• How fast does appetite change? Often within a week. If nothing changes by week 3-4, check in with your clinician.
• Will I gain a lot of weight? Responses vary. Some gain a few pounds over weeks; others barely move the scale. Diet quality and dose matter.
• Any lab tests needed? Not usually for allergies. If used for appetite or migraines, your clinician may track weight, growth charts, and side effects.
• Can pregnant people take it? Data is limited. Other antihistamines are usually preferred. Always talk with your OB first.

Risks and how to lower them

• Daytime drowsiness: favor bedtime dosing; avoid alcohol; don’t drive until you know your response.
• Constipation and dry mouth: fluids, fiber, sugar-free gum; consider stool softeners if your clinician agrees.
• Weight creep: plan your snacks; prioritize protein and healthy fats; set a weekly weigh-in.
• Drug interactions: give your prescriber a full med list, including sleep aids, cold meds, and herbal products.

When to call the doctor now

• Severe sleepiness, confusion, difficulty urinating, or vision changes
• Wheezing or chest tightness with thicker phlegm
• No improvement after 2-4 weeks (for allergies), or no appetite benefit after 4-8 weeks
• Any signs of an allergic reaction to the medicine

Next steps / Troubleshooting

• If your main goal is allergy control and you feel too sleepy: switch to a non-drowsy antihistamine during the day and reserve a small Periactin dose for bedtime, or stop if not needed.
• If appetite is the goal and mornings are groggy: concentrate the dose at bedtime and move breakfast a bit later; pair with calorie-dense foods you already like.
• If migraines don’t budge after 4-6 weeks: talk with your clinician about other preventives (e.g., propranolol, topiramate, nutraceuticals like magnesium)-don’t keep pushing a plan that isn’t working.
• If constipation hits hard: add fiber and fluid immediately; ask about a gentle stool softener; consider lowering the morning dose.
• If your child’s school performance dips: get teacher feedback, adjust dosing time, or consider a different medication.

Citations I trust for decisions here: FDA cyproheptadine prescribing information (for dosing, contraindications, and side effects), American Academy of Allergy, Asthma & Immunology practice insights on first-generation antihistamines, standard pediatric pharmacology texts on off-label appetite and migraine use, and toxicology guidelines on serotonin syndrome management. Bring your context-age, goals, other meds-to your prescriber so you land on a plan that fits real life. That’s what I do for my own family, between lunch boxes and late-night laundry.