BackgroundAlopecia X is a common cause of noninflammatory alopecia in Pomeranian dogs. In the past, treatment with growth hormone injections resulted in hair regrowth in many individuals. Progesterone can induce mammary‐derived growth hormone and is used to treat dogs with congenital growth hormone deficiency.Hypothesis/ObjectivesTo determine whether progesterone induces endogenous insulin‐like growth factor‐1 (IGF‐1) and causes hair regrowth in dogs with alopecia X.AnimalsEight neutered Pomeranian dogs with alopecia X for 1–2 years.MethodsIn part 1, two male and three female dogs received 5 mg/kg medroxyprogesterone acetate injected subcutaneously (s.c.) every 4 weeks for a total of four injections. In part 2, one male and two female dogs received 10 mg/kg medroxyprogesterone acetate injected s.c. every 4 weeks for four injections. Dogs were monitored monthly with physical examinations and complete blood counts, chemistry panels and urinalyses. In part 3, two coated Pomeranian dogs and two normal‐coated small breed dogs received two s.c. injections of 10 mg/kg medroxyprogesterone acetate. Serum was saved from each visit for IGF‐1 analysis.ResultsIn part 1, two dogs had partial hair regrowth of ~40–60%. In part 2, one dog had partial hair regrowth and one dog had complete hair regrowth 2 months after completion of the study. Unlike the normal‐coated dogs, whose IGF‐1 concentrations increased, the IGF‐1 concentrations in alopecic and coated Pomeranian dogs were low and remained unchanged. No adverse effects were noted.Conclusions and clinical importanceResults of this study showed that medroxyprogesterone injections resulted in partial hair regrowth in three and complete hair regrowth in one of eight Pomeranian dogs with alopecia X.