Melatonin
Melatonin is a naturally occurring hormone produced by the pineal gland that plays a key role in regulating sleep-wake cycles and photoperiod-dependent functions. In veterinary medicine, it is primarily used for: * **Dermatologic conditions:** Alopecia-X (especially in Nordic breeds), canine pattern baldness, and recurrent flank alopecia. * **Behavioral and sleep disorders:** Managing nocturnal pacing/activity in geriatric dogs and cats, as well as phobias and separation anxiety. * **Reproductive management:** Reversible estrus suppression in cats and adjusting seasonal fertility in sheep, goats, and horses. * **Endocrine support:** Adjunctive treatment for adrenal disease in ferrets. > **Clinical Pearl:** Melatonin is often considered a safe, first-line, low-cost trial for non-inflammatory alopecias before pursuing more aggressive endocrine diagnostics or treatments.
Mechanism: Melatonin is involved in the neuroendocrine control of photoperiod-dependent molting, hair growth, and pelage color. * **Hair Growth:** It stimulates winter coat growth; spring shedding occurs when melatonin levels decrease. The exact mechanism is unknown but may involve direct effects on the hair follicle or alteration of **prolactin** and/or **melanocyte-stimulating hormone (MSH)** secretion. * **Endocrine Effects:** Increases serum prolactin and growth hormone levels, and enhances the response to growth hormone-releasing hormone. Long-term use may decrease **luteinizing hormone (LH)**. * **Antioxidant:** Acts as a potent free radical scavenger.
Dosing by species
- Sleep disorders (nocturnal activity) ยท 3-12 mg (total dose) ยท PO ยท q12-24h
- Suppression of estrus ยท 18 mg implant ยท SC ยท Once ยท Suppresses estrus for 2-4 months
- Reduction of gastric ulcers in young pigs ยท 5 mg/kg in feed ยท PO ยท Continuous in feed
- Adjunctive treatment of adrenal disease ยท 0.5-1 mg per ferret ยท PO ยท q24h (7-9 hours after sunrise) ยท Can also use 5.4 mg implant which releases over 3-4 months. Better response in fall/winter.
- Adjunctive treatment of adrenal disease ยท 1-2 mg per ferret ยท PO ยท q24h ยท Or use 5.4 mg implant. May cause excessive drowsiness in ferrets under 600 grams.
- Alopecia-X, canine pattern baldness, or recurrent flank alopecia (experimental) ยท One to four 12 mg implants SC. Retreatment may be necessary once or twice a year. Alternatively, 3-6 mg PO q8-12h. ยท SC/PO ยท q8-12h (PO) or 1-2 times/year (SC) ยท Recommend having owners sign a release form noting the 'experimental' nature of treatment.
- Canine recurrent flank alopecia or seasonal flank alopecia ยท 2-3 mg per dog (up to 10 mg used) ยท PO ยท q24h for 3-5 days weekly or monthly, or daily ยท Improvement usually seen in 1 month, maximal in 3 months
Routes of administration
Contraindications
- Pregnancy
- Sexually immature animals
- Hepatic insufficiency (in humans)
- No information available
Adverse effects
- Sedation or drowsiness
- Altered sex hormone secretion and fertility
- Sterile abscesses at subcutaneous implant sites
- No information available in monograph (generally well tolerated, may cause mild sedation)
Drug interactions
- Benzodiazepines ยท Melatonin may potentiate sedative effects
- Succinylcholine ยท Melatonin may potentiate neuromuscular blocking effects
Monitoring
- Clinical efficacy (e.g., hair regrowth, improved sleep patterns)
- Hair regrowth (evaluate after 4-6 weeks of therapy)
Overdose
Little information is available; it is unlikely to cause significant morbidity after a single overdose. Treat symptomatically if profound sedation occurs.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.