The topic of spaying and neutering pets has always been a controversial one. There isn’t a single “right” answer for every animal, and veterinarians, researchers, and pet parents don’t all agree on the when, why, or how.
As awareness grows around the long-term hormonal consequences of spaying and neutering, many pet parents are beginning to ask a new question: Can hormone replacement therapy (HRT) support spayed or neutered animals – and if so, is it safe?
In response, some veterinarians are beginning to offer hormone-based interventions, including with hormone suppression implants that inhibit luteinizing hormone (LH), such as Suprelorin® (deslorelin acetate).
But what we actually know about their safety?
What is Suprelorin?
Suprelorin is a sustained-release implant containing deslorelin acetate, a synthetic gonadotropin-releasing hormone (GnRH) super-agonist.
At first glance, that sounds like it would stimulate hormone production, but paradoxically, when GnRH is continuously overstimulated, the body responds by shutting the system down.
Suprelorin acts on the hypothalamic–pituitary–gonadal (HPG) axis:
- The implant initially causes a temporary surge (“flare-up”) in LH, FSH, and testosterone
- With continuous exposure, the pituitary gland becomes desensitized
- Production of LH (luteinizing hormone) and FSH (follicle-stimulating hormone) is suppressed
As a result:
- Testosterone production drops dramatically
- Sperm production stops
- Libido decreases
- Testicles shrink in size
- Adrenal testosterone production is also reduced
In effect, Suprelorin is a form of non-surgical chemical castration.
Is Suprelorin Safe?
Suprelorin has been available since 2007 and is approved for specific uses depending on species and country:
Canada & other countries: Approved for healthy, sexually mature, intact male dogs and ferrets to induce temporary infertility
United States: Approved for ferrets, but not dogs
In approved uses, Suprelorin is generally considered safe for chemical castration in adult, intact male dogs when used exactly as approved.
However, safety data becomes more complicated when we look closely at the studies.
The company that formulated and distributes Suprelorin, Virbac, has done a study on the drug’s safety in juvenile dogs. The study involved 32 dogs in total (16 males, 16 females), with treatment starting at 12 weeks of age. The groups received either a placebo or a 1x, 3x, or 5x dose.
(You can read more about the full study here, but please be advised, the content is sensitive and may be disturbing to some readers 😓)
Reported adverse findings included:
- Hair loss, skin redness, scabbing
- Behavioural changes (excitedness, aggression during handling)
- Undescended testicles (expected with hormonal suppression)
- Diarrhea, blood at rectum
- Lumps at injection sites
- Grand mal seizures in one male and one female at the 5x dose (cause undetermined)
- Increased cholesterol (3x and 5x groups)
- Increased alkaline phosphatase
- Decreased bone mineral density in high-dose males
- Delayed growth plate closure in multiple groups
- Microscopic atrophy of reproductive organs in both males and females
While many of these findings were described as “expected,” they highlight the powerful systemic effects of long-term hormonal suppression, particularly in developing animals.
Additionally, it’s really, really important to note, since it’s being talked about with regard to hormone support, that it has NOT been tested in spayed or neutered animals. Its use in these animals is off-label. Safety, efficacy, and long-term effects are unknown. Using Suprelorin in already sterilized animals is experimental, and the short and long-term effects are unknown.
This is a critical distinction for pet parents to understand.
And… Suprelorin is approved in some regions to delay first estrus in pre-pubertal female dogs BUT there are no robust safety studies in adult females. According to Virbac, the only female data comes from the juvenile puppy study above. This means safety conclusions for adult female dogs are limited and uncertain.
A New and Evolving Area of Veterinary Medicine
Hormone replacement therapy for spayed and neutered animals is very new. It requires:
- Skilled veterinary supervision
- Conservative dosing
- Ongoing monitoring
- An understanding that long-term outcomes are not yet fully known
The Parsemus Foundation maintains a directory of veterinarians in the US and Canada offering these services: https://www.parsemus.org/vet-directory/
Final Thoughts
Every animal – and every household – is different. Decisions around spaying, neutering, hormone suppression, or hormone replacement should be made based on:
- Breed and size
- Age and developmental stage
- Temperament and behaviour
- Lifestyle and management ability
- Willingness to commit to training and responsibility
As with any emerging therapy, informed consent, transparency, and caution matter just as much as innovation.
