Zyactin contains cyproheptadine 4 mg, a sedating antihistamine. It is used for allergic conditions and itching, and it is also widely known for increasing appetite — which is why many people are given it to help with weight gain. It causes significant drowsiness and is not suitable for everyone.
What is Zyactin?
Zyactin contains cyproheptadine 4 mg in tablet form and is Schedule 2 in South Africa, available from a pharmacist.
Cyproheptadine is a first-generation antihistamine, but it acts on more than histamine. Three actions matter:
| Receptor blocked | Effect |
|---|---|
| Histamine H1 | Reduces allergic symptoms and itching |
| H1 in the brain | Marked drowsiness |
| Serotonin (5-HT) | Increases appetite; used in some other settings |
| Muscarinic | Dry mouth, blurred vision, constipation |
The serotonin-blocking action is what makes cyproheptadine distinctive. Serotonin helps signal fullness, so blocking it tends to increase hunger. That is a genuine pharmacological effect, not a rumour — and in South Africa it is a major reason the medicine is requested.
That popularity brings a problem worth stating plainly. Cyproheptadine is sometimes used, unsupervised, purely as a weight-gain aid — including in ways it was never intended for and in people it is not suitable for. The weight gained is largely fat and fluid rather than muscle, the effect stops when the medicine stops, and the drowsiness and other effects continue throughout. If weight gain is the goal, it is worth discussing with a doctor rather than self-treating, because unintentional weight loss usually has a cause worth finding.
Unlike newer antihistamines such as cetirizine, cyproheptadine crosses readily into the brain, which is why it sedates so noticeably.
What is Zyactin commonly used for?
- Allergic rhinitis and hay fever — sneezing, runny nose, itchy eyes.
- Hives (urticaria) and allergic skin reactions.
- Itching, including from eczema, insect bites and chickenpox, where the sedation also helps sleep.
- Appetite stimulation, in people with poor appetite or unintended weight loss, under medical supervision.
- Cold urticaria, a specific condition where cold triggers hives.
- Migraine prevention, occasionally, particularly in children.
- Serotonin syndrome, in hospital settings, using its serotonin-blocking action.
For daytime allergy control in someone who needs to drive, work or study, a non-sedating antihistamine is the better choice. Cyproheptadine suits situations where sedation is acceptable, or where the appetite effect is actually wanted.
It treats symptoms rather than causes, and has no effect on infection.
How Zyactin fits into this medicine category
| Group | Examples | Notes |
|---|---|---|
| Sedating antihistamines | Cyproheptadine (Zyactin), chlorphenamine, promethazine | Allergy and itch; marked drowsiness |
| Non-sedating antihistamines | Cetirizine, loratadine | Allergy without significant sedation |
| Steroid nasal sprays | Fluticasone, budesonide | Most effective for persistent allergic rhinitis |
| Decongestants | Pseudoephedrine, oxymetazoline | Short-term nasal blockage |
| Leukotriene blockers | Montelukast | Allergic rhinitis with asthma |
For ongoing allergic rhinitis, a steroid nasal spray usually outperforms any antihistamine tablet. See the allergy, cold, flu and respiratory medicines hub.
What to check before using Zyactin
Do not drive or operate machinery. The drowsiness is substantial and can persist into the next day.
Speak to a pharmacist or doctor first if you:
- Are giving it to a child. Cyproheptadine is not suitable for infants, and children can react with agitation rather than sedation. Age and weight determine suitability — ask before giving it.
- Are elderly. Confusion, sedation, falls, constipation and urinary retention are all more likely, and this class of medicine is generally best avoided in older people.
- Have glaucoma, particularly narrow-angle.
- Have prostate enlargement or difficulty passing urine.
- Have asthma, COPD or other breathing problems.
- Have a stomach ulcer or any bowel obstruction.
- Have epilepsy.
- Have heart disease, high blood pressure or an overactive thyroid.
- Have liver or kidney disease.
- Are pregnant or breastfeeding. It can suppress milk production.
- Take an MAOI antidepressant — this combination should be avoided.
- Take any other sedating medicine, including alcohol, opioids, benzodiazepines or sleeping tablets.
Do not drink alcohol with it. The sedation compounds.
Possible cautions and when to ask a pharmacist or doctor
Common effects are drowsiness, increased appetite and weight gain, dry mouth, blurred vision, dizziness, constipation and difficulty passing urine.
Seek medical attention if you notice:
- Marked confusion, agitation or hallucinations, particularly in a child or an older person.
- Restlessness or excitability instead of drowsiness — a recognised paradoxical reaction, more common in children.
- Inability to pass urine.
- A fast or irregular heartbeat.
- A seizure.
- Yellowing of the eyes or skin.
- Swelling of the face, lips or tongue, or difficulty breathing.
- Severe rash or blistering skin.
- Severe constipation or abdominal pain.
Weight gain on cyproheptadine should be a considered decision, not a side effect you drift into. If you are taking it for allergy and gaining weight you do not want, say so — a non-sedating antihistamine will treat the allergy without that effect.
If you are taking it for weight gain, it is worth asking a doctor why the weight is low in the first place. Unintended weight loss can reflect thyroid disease, diabetes, infection including TB and HIV, malabsorption, depression or cancer — all of which need treating in their own right, and none of which are addressed by stimulating appetite.
See a doctor if allergy symptoms persist despite treatment, if you need an antihistamine most days, or if a child taking it becomes unusually drowsy or agitated.
Related medicine guides
- Browse Allergy, Cold, Flu & Respiratory Medicines guides
- Read: Austell Cetirizine used for
- Read: Rhineton used for
Frequently asked questions
What are Zyactin tablets used for? Allergic conditions and itching — hay fever, hives, allergic skin reactions — and to stimulate appetite. Each tablet contains cyproheptadine 4 mg.
Does Zyactin make you gain weight? It increases appetite by blocking serotonin, and weight gain commonly follows. The gain is mostly fat and fluid, and it stops when the medicine stops.
Can I take it just to gain weight? It is used for that under medical supervision, but unintended weight loss usually has a cause worth investigating. Speak to a doctor rather than self-treating.
Does it make you sleepy? Yes, markedly, and the effect can carry into the next day. Do not drive or operate machinery.
Is Zyactin the same as cetirizine? No. Both are antihistamines, but cetirizine is non-sedating and does not stimulate appetite.
Can children take it? Only on advice. It is unsuitable for infants, and children may become agitated rather than sleepy. Ask a pharmacist about age and weight.
Can I drink alcohol with it? No. Alcohol adds substantially to the drowsiness.
How long can I take it for? Short courses are usual for allergy. Longer use, including for appetite, should be supervised by a doctor.