Related Products
Related Products
Geriatric HIMS in Small Dogs: When “Cushing’s” Isn’t Quite Cushing’s
Dr. Keith A Hnilica, DVM, MS, DACVD
Apr 9, 2026
6 min read
Geriatric HIMS—Hormone Imbalance with Melatonin Sensitivity—is a useful clinical label for older, usually small-breed dogs that look prematurely aged and “Cushingoid” but do not cleanly fit classic hyperadrenocorticism on routine testing. These dogs may show thin haircoat, recurrent pyoderma, skinfold dermatitis, urinary tract infections, pot-bellied or weakened body condition, lethargy, and immune fragility despite largely normal baseline lab work. Veterinary literature has long recognized debate around so-called “atypical Cushing’s,” especially cases involving abnormal adrenal sex-steroid patterns rather than obvious cortisol excess. 
Melatonin is not a cure-all, but it is one of the most interesting tools in this gray-zone population. In normal adult dogs, oral melatonin has been shown to lower estradiol and 17-hydroxyprogesterone, supporting the idea that it can influence sex-hormone balance. At the same time, older work in dogs with hair-cycle arrest found that hormone changes do not always neatly track clinical improvement, which means response may be real even when follow-up endocrine numbers stay confusing. 
That fits what many clinicians see: some geriatric, small-breed dogs with “almost Cushing’s” signs improve on higher-dose melatonin with better coat quality, calmer behavior, and fewer skin complications. The drug is widely used in veterinary medicine, has a broad safety margin, and adverse effects are usually mild—mostly sedation, lethargy, vomiting, or ataxia. Care is still needed because some human products contain xylitol or 5-HTP, which are dangerous for dogs. 
So, Geriatric HIMS is best viewed not as proven textbook disease, but as a practical syndrome: an aging, hormone-skewed, melatonin-responsive dog that deserves treatment before being dismissed as “just old.”