From Dog

Melatonin (N-acetyl-5-methoxytryptamine) is an endogenous growth hormone produced in many body tissues, including the pineal gland, retina and the gastrointestinal tract of dogs.

The biological clock, which determined longevity in dogs is dictated by daily (circadian) and seasonal (circannual) time. These time changes are mediated by the alteration of levels of melatonin, an evolutionary ancient hormone, which follows a circadian rhythm[1].

Melatonin production is controlled by nerve impulses from the suprachiasmatic nuclei. Melatonin synthesis, which is inhibited by light on the mammalian retina, peaks in plasma concentrations during the night[2].

Melatonin, synthesized from dietary tryptophan[3], affects physiological parameters within the dog, specifically immune-status (by regulation of neutrophil and lymphocyte activity)[4], reduction in oxidative stress[5] and production of estradiol, androstenedione, thyroxine and cortisol[6], extracellular water transport[7], cellular apotosis[8], seasonal hair growth, reproductive cycles and fertility, sleep cycles and stimulation of osteoblast activity[9].

Exogenous melatonin has been used pharmacotherapeutically for a number of canine diseases, including:

Recommended dose rate in dogs is 0.1 - 0.3 mg/kg daily orally.

Minor side-effects include skin allergies and disruption of normal corticosteroid production at higher doses.


  1. Bubenik GA & Konturek SJ (2011) Melatonin and aging: prospects for human treatment. J Physiol Pharmacol 62(1):13-19
  2. Dunlap KL et al (2007) Seasonal and diurnal melatonin production in exercising sled dogs. Comp Biochem Physiol A Mol Integr Physiol 147(4):863-867
  3. Fragua V et al (2011) Preliminary study: voluntary food intake in dogs during tryptophan supplementation. Br J Nutr 106(1):S162-S165
  4. Uzenbaeva LB et al (2012) The melatonin influences on neutrophils/lymphocytes ratio of mammals blood depends on age of animals. Adv Gerontol 25(3):409-414
  5. Cutando A et al (2007) Melatonin reduces oxidative stress because of tooth removal. J Pineal Res 42(4):419-420
  6. Fecteau KA et al (2011) Effect of combined lignan phytoestrogen and melatonin treatment on secretion of steroid hormones by adrenal carcinoma cells. Am J Vet Res 72(5):675-680
  7. Ramírez-Rodríguez G et al (2007) Melatonin increases stress fibers and focal adhesions in MDCK cells: participation of Rho-associated kinase and protein kinase C. J Pineal Res 42(2):180-190
  8. Chang CY et al (2010) Assessment of the tumorigenesis and drug susceptibility of three new canine mammary tumor cell lines. Res Vet Sci 88(2):285-293
  9. Muñoz F et al (2012) Topical application of melatonin and growth hormone accelerates bone healing around dental implants in dogs. Clin Implant Dent Relat Res 14(2):226-235
  10. Rachid MA et al (2003) Concurrent follicular dysplasia and interface dermatitis in Boxer dogs. Vet Dermatol 14(3):159-166
  11. Uchikawa O et al (2002) Synthesis of a novel series of tricyclic indan derivatives as melatonin receptor agonists. J Med Chem 45(19):4222-4239
  12. Saeidi M et al (2009) Effect of melatonin in the prevention of postoperative pericardial adhesion formation. Interact Cardiovasc Thorac Surg 9(1):26-28