As a hormone replacement therapy (HRT) user, I am particularly interested in this subject matter; however, something I had not considered nor discussed with my doctor was whether my HRT could impact others, including my animals.
It is estimated that there are around 13 million perimenopausal or menopausal women in the UK – that equates to around one-third of the entire female population. Some of the most common symptoms include vasomotor symptoms (eg hot flushes and night sweats), breast tenderness, insomnia, migraines and/or premenstrual dysphoria (Deecher and Dorries, 2007). Statistics from the NHS Business Services Authority show the number of patients prescribed HRT has risen by 35 percent from 2020/2021 to 2021/2022, with around 1.93 million patients on the drug (NHSBSA, 2022). It’s important to note that this figure does not include individuals treated privately.
What is hormone replacement therapy?
HRT is a treatment used to alleviate symptoms of menopause in women. It replaces hormones that are at a lower level as women approach and experience menopause. The preparations come in various forms, including gels, sprays, tablets and patches. Gels and sprays are applied to clean, dry and unbroken skin. Gels are usually applied on the upper arm, shoulder or inner thigh, while sprays are applied on the inner arm and patches are placed below the waist or on the thigh or buttock area.
Different HRT products are available; many, if not all, of which might accidentally be transferred to animals – from patches accidentally attaching themselves to pets’ paws, tablets being eaten and gels being licked.
HRT and animals – an unknown problem?
With over 12 million dogs living as pets in the UK (with 31 percent of UK households owning a dog) and around 11 million pet cats (with 26 percent of households owning a cat) (UK Pet Food, 2023), it follows that a proportion of these animals will be living with owners or carers who may be on HRT.
Most responses from the veterinary forums suggested there was a general lack of awareness relating to the risk of secondary exposure to hormone replacement therapy
Recently, several stories have highlighted the risk of HRT being absorbed by pets. For example, North Downs Specialist Referrals has recorded five cases of dogs being diagnosed with secondary exposure to HRT since the start of 2023. This included the case of Rosie, a Jack Russell Terrier that appeared to come into season despite being spayed. A simple search of the internet finds another case that made headlines in the veterinary press in 2017: Lily, a 12-week-old female Dachshund, was found to be in season – in human children, we would call this precocious puberty. Veterinary forums unearthed the following:
- Six cases of male neutered dogs with mammary development; one exhibited excessive humping and lots of discharge, while another also had an enlarged prostate
- Five cases of dogs with hair thinning and/or alopecia symptoms. One of these also had enlarged teats, which occurred after the owner had changed from oral HRT to transdermal
- One male neutered Vizsla showed signs of feminisation – the owner had recently started oestrogen gel
- A very young female puppy with a hugely enlarged vulva
- Two spayed cats showed signs of oestrus and mammary development – one was a Sphinx, and thus potentially at greater risk where the animal is hairless
However, most responses from the veterinary forums suggested there was a general lack of awareness relating to the risk of secondary exposure to HRT.
What’s in the literature?
Case studies have also been recorded relating to HRT toxicity in cats (Dresner and Norsworthy, 2013; Tater et al., 2019). Anecdotal evidence was put forward recently by one of my clients relating to her horse. However, there is even less data to support transference to horses, as much of the research has looked at young children and smaller animals like cats and dogs given their closer and more frequent physical contact with adults within the home setting. Hence, young children, cats and dogs are at greatest risk of HRT toxicity due to their size and early stage of development (Sjöström et al., 2022).
Indicators of HRT transference
Signs veterinary professionals can look out for that might indicate HRT transference:
- In females:
- Enlarged vulva
- Bloody discharge from the vulva
- Raising of the hindquarters
- Uterine infection
- In males:
- Shrunken penis
- Small testes and/or undescended testicles in dogs six months or older
- Inflamed penis
- In both sexes:
- Hair loss
- Increased interest from other dogs and/or attraction towards others
- Enlarged mammary glands and/or ulceration of the mammary glands
- Stunted growth
- Hypertrophied skin (scars)
- Excessive vocalisation
- Decreased appetite
- Extra-affectionate behaviour
- Inappropriate indoor urination
- Restlessness
- Aggression or other mood changes
- Vomiting and/or diarrhoea
- Any other abnormal behaviour that is out of character for the animal
Considerations for animal professionals
It’s possible that secondary exposure to HRT can be overlooked as a differential diagnosis when assessing animals. Sjöström et al. (2022) found that similar symptoms are observed in dogs with signs of ovarian remnant syndrome. While awareness has grown over recent years about the impact pseudopregnancy can have on entire and spayed female dogs thanks to the great work of practitioners like Sara Davies (Davies, 2023), considering whether HRT is at play may not be at the forefront of minds. After all, most practitioners would not necessarily discuss such intimate details with their clients unless the client raised them or the subject came up organically in conversation.
Considering whether hormone replacement therapy is at play may not be at the forefront of minds. After all, most practitioners would not necessarily discuss such intimate details with their clients
Veterinary research recommends taking bloods to examine oestradiol levels (regardless of gender) if HRT toxicity might be suspected, and ultrasonographic examination may help to rule out ovarian remnants in females.
Sarah Keir, a veterinary surgeon and ultrasonographic specialist, says: “Because ultrasonographic examination with a high-quality machine is not typically available to the majority of clinics, what is useful in cases where suspected hormonal changes may be at play is conducting an anti-Müllerian hormone test to look for any presence of ovarian or testicular tissue. We also need to be aware of when oestrogen replacement treatment is used to treat urinary incontinence in bitches; the neutered bitch may appear like she is in oestrus, so this is another differential that would need to be ruled out.”
Perhaps discussions with clients should include non-intrusive questioning to better understand if the animal comes into regular contact with anyone using hormone replacement therapy
So, for animal practitioners, perhaps discussions with clients should include non-intrusive questioning to better understand if the animal comes into regular contact with anyone using HRT, having reviewed the clinical history when considering diagnostic differentials.
