Periactin contains Cyproheptadine as its active component. Cyproheptadine is an antihistamine that belongs to the allergy-relief therapeutic class. The medication is supplied as a 4 mg pill and is available in Hong Kong only with a prescription from a qualified health professional. The Department of Health’s Pharmacy and Poisons Board classifies it as a prescription-only drug.
Cyproheptadine blocks the action of histamine at H1 receptors, which are key mediators of allergic reactions such as itching, swelling, and runny nose. In addition to its antihistamine effect, Cyproheptadine antagonizes serotonin (5-HT₂) receptors, which contributes to its ability to stimulate appetite and to mitigate certain serotonin-related symptoms. After oral administration, the tablet is absorbed from the gastrointestinal tract, reaching peak plasma concentrations within 2 hours. It is extensively metabolised in the liver and excreted primarily via the kidneys. The combined H1-blocking and serotonin-antagonist actions explain why the drug can relieve allergy symptoms and, in some cases, increase appetite.
Periactin is approved in Hong Kong for the relief of symptoms associated with allergic conditions, including:
The medication is intended for use in adults and older children for whom the prescribing clinician determines it is appropriate.
Research and clinical guidelines have explored additional applications of Cyproheptadine beyond its primary allergy indication. When used off-label, the medication must be prescribed and monitored by a qualified health professional.
Off-label use requires medical supervision and individualized risk assessment.
If you fall into any of the above groups, discuss alternatives with your healthcare provider.
These effects are generally mild and tend to improve as the body adapts to the medication.
If you are taking other medications, supplements, or herbal products, inform your pharmacist or prescriber before starting Periactin.
Standard dosing: The usual adult regimen is 4 mg taken 2 to 4 times daily, depending on symptom severity and clinician judgment.
Special populations:
Elderly or patients with liver disease: Begin with 4 mg once daily and adjust slowly.
Renal impairment: Dose may need reduction; follow your prescriber’s guidance.
Administration: Swallow the tablet whole; do not crush or chew.
Missed dose: If you forget a dose and it is within a few hours of the scheduled time, take it. If it is close to the next dose, skip the missed one-do not double up.
Overdose: Symptoms may include extreme drowsiness, rapid heart rate, or seizures. Seek emergency medical assistance immediately; supportive care is the mainstay of treatment.
Discontinuation: For chronic use, a gradual taper is advisable to minimise rebound itching or other withdrawal phenomena.
Dosage must always be individualized by your prescribing clinician.
This article provides educational information about Periactin and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.
Periactin is not indicated for asthma management. While it may relieve allergic rhinitis that can coexist with asthma, specific asthma medications should be used for bronchial symptoms.
If sedation interferes with daily activities or safety (e.g., driving), contact your prescriber. They may adjust the dose, change the dosing time, or consider an alternative antihistamine.
Periactin tablets in Hong Kong are typically white, round, and scored, bearing the imprint “4 MG”. Tablet appearance can vary by manufacturer and region, so always verify the imprint and dosage before use.
Cyproheptadine is not listed as a prohibited substance by the World Anti-Doping Agency (WADA). However, athletes should disclose all medications to their sport’s medical team to avoid inadvertent violations.
Concurrent use of multiple antihistamines generally increases the risk of side effects such as sedation and dry mouth. Combining them should only occur under direct medical supervision.
Most patients notice improvement within 30 minutes to 2 hours after the first dose, with maximal effect observed after several days of consistent use.
St. John’s wort is a known CYP2D6 inhibitor and may raise Cyproheptadine levels, potentially increasing side-effect risk. Discuss all supplements with your healthcare provider.
Do not flush medications down the toilet. Return unused pills to a pharmacy medication-take-back program or follow local hazardous waste disposal guidelines.
Safety in pregnancy has not been established; animal studies suggest possible risk, particularly in the first trimester. It should be used only if the potential benefit outweighs the risk, and under professional guidance.
Increased appetite is a known effect, and some patients may experience modest weight gain with prolonged therapy. Monitoring dietary intake and discussing concerns with a clinician can help manage this effect.
