Vet Guide to Cyproheptadine in 2025 🐾

Hi, I’m Dr Duncan Houston BVSc—founder of Ask A Vet. In this comprehensive 2025 guide, we explore cyproheptadine, a first-generation antihistamine used off-label in dogs and cats. It’s a versatile tool: stimulating appetite in cats, managing allergic or respiratory conditions, and countering serotonin syndrome. Learn how it works, dosing, safety, side effects, and monitoring strategies to support your pet’s health. 🐶🐱

📘 What Is Cyproheptadine?

Cyproheptadine is a first-generation antihistamine (brand name Periactin®) that blocks H₁ histamine and serotonin receptors. In veterinary medicine, it’s used off-label as:

• An appetite stimulant in cats—especially during illness or chemotherapy :contentReference[oaicite:3]{index=3}.
• An aid in allergic conditions—like atopic dermatitis or feline asthma :contentReference[oaicite:4]{index=4}.
• A treatment for serotonin syndrome in dogs and cats by blocking excess serotonin receptors :contentReference[oaicite:5]{index=5}.

✅ Why Vets Prescribe It

• Appetite boosting in cats: end-stage kidney disease, chemotherapy, or chronic illness :contentReference[oaicite:6]{index=6}.
• Allergy support: used adjunctively for itchy skin or mild asthma :contentReference[oaicite:7]{index=7}.
• Serotonin syndrome antidote: blocks serotonin receptors in overdose or toxicity :contentReference[oaicite:8]{index=8}.

📐 Dosing Guide

🐱 Cats (appetite stimulant):

• 1–4 mg per cat, given once or twice daily. A common starting point is 2 mg every 12 hours :contentReference[oaicite:9]{index=9}.
• May take 2–3 days to see effects :contentReference[oaicite:10]{index=10}.

🐶 Dogs (allergy or serotonin syndrome):

• 0.3–2 mg/kg twice daily for allergy relief :contentReference[oaicite:11]{index=11}.
• Dose tailored by pet weight and condition; dogs don’t typically get appetite benefit :contentReference[oaicite:12]{index=12}.

Armed with food or water to reduce gastric upset; tablets can be hidden in treats or capsules. Use veterinary formulations or compounds when necessary :contentReference[oaicite:13]{index=13}.

⏱️ How It Works & Onset

Cyproheptadine’s dual H₁ and 5-HT₂C antagonism leads to appetite stimulation and itch relief. Cats typically respond in 2–3 days; dogs may show allergy improvement within 1–2 weeks :contentReference[oaicite:14]{index=14}. In serotonin syndrome, effects can be swift once serotonin receptors are blocked.

⚠️ Side Effects & Safety

Common mild effects:

• Drowsiness or sedation (common) :contentReference[oaicite:15]{index=15}.
• Dry mouth, possible urinary retention :contentReference[oaicite:16]{index=16}.
• Hyperexcitability in cats—may manifest as restlessness :contentReference[oaicite:17]{index=17}.

Serious signs (less common):

• Elevated heart rate, urinary obstruction—use with caution in BPH or glaucoma :contentReference[oaicite:18]{index=18}.
• Overdose signs: seizures, significant hyperexcitability, dry mouth, urinary issues—seek immediate care :contentReference[oaicite:19]{index=19}.

🚫 Contraindications & Interactions

• Avoid in pets with urinary tract blockage, glaucoma, or GI obstruction :contentReference[oaicite:20]{index=20}.
• Use cautiously if pet is on several sedatives or anticholinergics.
• Not FDA-approved for veterinary use; always use vet-provided or compounded meds :contentReference[oaicite:21]{index=21}.

🩺 Monitoring & Follow-Up

• Check daily for appetite changes (cats), energy, urinary function, and sedation.
• Stop drug and consult vet if urinary retention, severe restlessness, or tachycardia occur.
• For serotonin syndrome in dogs, use as directed in emergency protocols.

⏳ Missed Dose & Overdose Handling

• Missed dose? Administer when remembered; do not double dose within 12 hours.
• Overdose? Signs include extreme sedation or agitation, urinary trouble, tachycardia, seizures—visit emergency vet or poison control :contentReference[oaicite:22]{index=22}.

🏡 Real‑World Cases

🐱 Cat with Decreased Appetite during Chemotherapy

• 2 mg cyproheptadine twice daily. Appetite picks up in 3 days. Continue until appetite stabilizes.

🐶 Dog with Mild Atopic Dermatitis

• 1 mg/kg twice daily for 2 weeks. Adds mild itch relief; consider adding stronger antihistamine or immunotherapy.

🐶 Serotonin Syndrome Management

• Emergency dose under vet – cyproheptadine can help block serotonin after drug overdose.

❓ FAQs

Can I give human Periactin to my pet?

Only under veterinary instructions. Human doses may differ, and pet-friendly formulations reduce risk. Never dose without vet approval :contentReference[oaicite:23]{index=23}.

Is sedation permanent?

No—most pets adapt within days. If sedation persists, discuss dose adjustment.

How long is treatment needed?

Depends on condition: appetite stimulant until eating improves; allergy use is temporary or adjunctive depending on response.

📌 Final Takeaways

• Cyproheptadine is an off-label antihistamine useful in appetite stimulation (cats), mild allergy support, and serotonin syndrome management.
• Dosing: cats 1–4 mg once/twice daily; dogs 0.3–2 mg/kg twice daily for allergies or serotonin issues.
• Expect drowsiness and possible dry mouth; monitor urinary and cardiac function.
• Avoid use in obstruction cases; use only under veterinary supervision.

Want help using cyproheptadine for your pet’s appetite, allergies, or emergency support? Download the Ask A Vet app for 24/7 vet guidance, dosing schedules, symptom trackers, and peace of mind. We’re here to help your pet thrive in 2025 and beyond! 🐾❤️