Estrogen toxicity in dogs occurs when they are exposed to female sex hormones, either suddenly (acute exposure) or over a longer period (chronic exposure). The complications from this exposure vary depending on the dose and duration of exposure.

Example of a human HRT patch ©Vetstream Ltd

Estrogen is a hormone produced by the ovaries. Medicines containing estrogen compounds are used as contraceptives, hormone replacement therapies (HRT) or for other medical treatments. HRT patches, gels and sprays are commonly prescribed to support women through menopause. Some human estrogen products (patches, gels and sprays) are designed to be absorbed through the skin and your dog’s skin can absorb the products in the same way as human skin, or dogs may lick the product off their fur when grooming themselves. Dogs may be exposed to estrogen by eating or chewing the products, or snuggling with owners wearing exposed HRT products or repeated contact with recently treated skin. Rural/farm dogs may also come into contact with estrogen-impregnated intravaginal sponges. These products are used to enhance reproductive function in sheep and curious dogs may lick or eat discarded sponges.

If your dog has a single exposure to a hormone product (such as oral contraceptives) then they are unlikely to suffer any ill effects. Very occasionally ingestion of an estrogen product may cause mild wobbliness and drowsiness, but these signs wear off without treatment. If your dog is regularly exposed to these hormones, from licking gels or from snuggling near an applied HRT patch or recently applied gel then this chronic exposure could result in signs of toxicity such as reduced appetite, more lethargic than usual, signs of estrus (coming into season – even if very young or neutered), hair loss or enlarged mammary glands/nipples (even in male dogs). Female dogs may have some disruption to their estrus cycle and can be prone to a pyometra (infection in the uterus) or a stump pyometra in neutered dogs. Estrogen can also suppress bone marrow production which can be very serious, but it is unlikely that dogs would be exposed to high enough doses of human estrogen products for this to be problematic. If your dog has ingested a patch or intravaginal sponge, then as well as the hormonal effects, the product could cause a blockage within their gastrointestinal system. In these cases, your dog may seem lethargic, unhappy, may vomit or have diarrhea and may seem painful when their abdomen is touched. If your dog is showing any of these symptoms, they will need to attend your veterinary practice who will be able to advise on the next steps.

Your veterinarian will diagnose this condition primarily by reviewing your dog's history of possible hormone exposure and ruling out other conditions that could cause similar symptoms. It's important to tell your vet about any hormone medications in your home, even if you're not sure your dog has been exposed to them. Many dogs will not require treatment for exposure to HRT but in some cases particularly if an HRT patch or intravaginal sponge has been ingested, there can be complications.

The main treatment is identifying and removing the source of hormone exposure. Once exposure stops, most dogs will gradually return to normal. However, if your dog is unwell your veterinarian may prescribe some supportive treatments to help them recover faster. If your dog has ingested an HRT patch or intravaginal sponge, the risk of the foreign body in the gastrointestinal system is greater than the toxicity of HRT. In some cases, surgery may be required to remove the blockage.

Most dogs recover fully, though in cases of long-term exposure, it may take several months for all symptoms to disappear.

Keep medications safely out of your dog's reach. Store these items in sealed containers or in closed cabinets. Make sure to inform all family members and house guests about this hazard. Wash your hands after applying any HRT products and ensure that patches are covered by clothing and that gels have dried and the area is covered by clothing, before handling your dog. Ideally, apply your patch in an area you will notice if it falls off or where it will be caught by clothing to reduce the risk of accidental ingestion. Dispose of used patches safely; they should be folded in half with the adhesive side inwards and discarded securely in the bin.

Contact your veterinarian if you notice any unusual changes in your dog's behavior, eating habits, or physical appearance, or if they have had vomiting or diarrhea, especially if you have hormone medications in your home.