Pet owners who use prescription hormone replacement or birth control medications can accidentally expose their pets to the drugs. Female cats with hormone toxicity, even those that have been spayed, can exhibit symptoms of estrus such as swollen vulva and bloody discharge. Male cats may experience shrinking of the penis and testicles, while both sexes can suffer from hair loss, anemia, swollen mammary glands and increased potential for mammary tumors.

In years past, hormone medications for women were dispensed predominantly in pill form. A cat might get into a pack of pills and ingest the drug, but the one-time exposure was unlikely to cause a medical emergency. Recently, however, both birth control and hormone replacement drugs are commonly dispensed in the forms of gels, creams, patches or sprays. These medications are applied topically, often in locations such as the wrists or inner arms with inadvertent exposure taking place when the cats are carried or stroked. A cat may also lick the medication from the owner's skin or from its own fur if the drug has been accidentally rubbed onto it. Proper diagnosis and treatment of this disorder requires a visit to the veterinarian.

While some of the symptoms of hormone replacement drug poisoning in cats can only be detected via laboratory tests, certain symptoms will be obvious. Some of the symptoms will be different depending on the sex of the cat and whether or not it has been spayed or neutered. Contact your veterinarian if you observe the following:

There are several potential causes of hormone drug toxicity in cats, including:

Certain symptoms of hormone replacement poisoning will be obvious, including estrus behavior in a spayed female cat or swollen mammary glands in a male. Getting to the underlying cause, however, may require some detective work. Be prepared to disclose any medications taken by you or anyone in your household, as HRT drugs may be the culprit. Even if HRTs are suspected as the cause of your cat's problems, your veterinarian will likely conduct a series of tests to confirm the diagnosis and to discover the severity of the exposure. In addition to a complete physical examination that includes visual inspection of external symptoms and palpation of internal organs, expect your veterinarian to perform some or all of the following:

If exposure to human HRTs is diagnosed as the cause of your cat's illness, the severity and duration of the exposure will determine the course of treatment. In mild cases, simply eliminating the method of exposure can allow the symptoms to reverse over time. However, prolonged exposure can lead to secondary issues that may need to be addressed.

Swelling of the mammary glands in both males and females is common with hormone replacement poisoning. Swelling often resolves on its own when the exposure is discontinued. In some cases, however, hormone poisoning can lead to cysts or tumors developing in the mammary glands. Tumors that do not recede on their own may need to be removed surgically.

Although rare, prolonged exposure to toxic levels of hormones can cause a condition called aplastic anemia. This occurs when the bone marrow stops producing blood cells. Blood transfusions may be necessary to treat the anemia. Once the cause of the hormone toxicity is resolved, bone marrow damaged from the exposure will typically begin to function again but blood counts will need to be monitored to determine if additional transfusions are needed.

If your cat is suffering from symptoms of a medication prescribed by your vet, the dose may need to be adjusted or the treatment changed or discontinued. 

Once the cause of hormone replacement poisoning is removed, most cats will eventually make a complete recovery. Regular follow-up visits to the veterinarian will be in order to test red and white blood cell counts and hormone levels to ensure that everything is returning to normal. If surgery was required, your vet will discuss post-operative care which may involve administering medications or returning to the clinic for suture removal. Transfusions may need to be repeated. Antibiotics may be prescribed if underlying infection was discovered.

Preventing future exposure is the key to long-term recovery for your cat. Topical HRT medications may need to be applied to areas that eliminate your cat's access. The simple act of washing hands after application can reduce the likelihood of exposure. Some hormone products delivered via creams or gels can be taken in pill form instead. Ensuring that the cat cannot reach the medication is critical for preventing a recurrence of poisoning.