Estrogen containing products, including oral contraceptives and hormone replacement therapy, can cause serious adverse effects and toxicity in pets. While ingestion of these medications pose toxicity risks, topical exposure is also concerning. Notable hair loss has been seen in animals exposed to topical hormone replacement therapy products.

Dogs and ferrets are indicated for this toxicity.

Signs and symptoms of toxicity: Clinical signs of toxicity include hair loss, female genital swelling, male genital atrophy, weakness and loss of coordination.

Toxic consumption:
In dogs, greater than 1 mg/kg (0.45 mg/lb) of estrogen may be toxic. It should be noted that oral contraceptives typically contain 0.02-0.05mg of estrogen per tablet.

Dogs: Estrogen Toxic Consumption
X-Small Yorkie, Chihuahua	Small Pug, Boston Terrier, Poodle	Medium Beagle, Scottish Terrier	Large Boxer, Cocker Spaniel	X-Large Retriever, German Shepherd	XX-Large Great Dane, St. Bernard
1 – 10 lbs. (0.45 – 4.6 kg)	11 – 25 lbs. (5 – 11.4 kg)	26 – 40 lbs. (11.8 – 18.2 kg)	41 – 70 lbs. (18.6 – 31.8 kg)	71 – 90 lbs. (32.3 – 40.9 kg)	91 – 110 lbs. (41.4 – 50 kg)
> 0.45 mg	> 5 mg	> 11.8 mg	> 18.6 mg	> 32.3 mg	> 41.4 mg

References:
– Berger D. Canine Alopecia Secondary to Human Topical Hormone Replacement Therapy in Six Dogs. J Am Anim Hosp Assoc 2015;51:136-142. DOI 10.5326/JAAHA-MS-6247
– Sontas H. Estrogen-induced myelotoxicity in dogs: A review. Can Vet J 2009;50:1054-1058.