Overview
Chemical castration is a non-surgical way to stop a dog from having puppies, either temporarily or, less commonly, for good. It’s most often done using a slow-release hormone implant, which suppresses testosterone in male dogs. It can also involve hormone treatments to delay seasons in female dogs.
Chemical castration offers a reversible alternative to surgical neutering, making it a suitable option for owners who want to manage fertility without permanent surgery. It typically lasts between six and 12 months, depending on the implant used, and is widely available across UK veterinary clinics.
Why do chemical castration in dogs?
Owners might consider chemical castration for several reasons:
To see how their dog’s behaviour or health changes after castration, without making it permanent
They’re still unsure about breeding in future
It’s useful for dogs who can’t have a general anaesthetic or for those with health risks
No incision means no post-surgical recovery period
They prefer the simplicity of an implant over a surgical procedure
How long does chemical castration last in dogs?
The most common chemical castration method in male dogs, an implant, takes effect within four to six weeks for the 4.7mg implant or up to eight weeks for the 9.4mg implant. During this period, male dogs may still be fertile, so it’s important to avoid contact with females in heat. After this window, testosterone levels and sperm production drop significantly. The procedure lasts:
Around 6 months for the 4.7 mg implant
At least 12 months for the 9.4 mg implant
These timings can vary depending on your dog’s breed, size, age, and hormone levels. You should plan your next implant about a month before the old one is due to expire.
Is chemical castration permanent?
Permanent chemical castration exists, but it's not widely used in the UK. It usually involves an injection into the testicles that causes lasting damage to the sperm-producing tissue. While this approach can work, it’s considered far more invasive and isn’t authorised for use on dogs in the UK.
What are the side effects of chemical castration?
Most dogs tolerate the procedure well, but some side effects are possible:
Brief surge in testosterone levels in the first few weeks, possibly increasing behaviours like mounting or marking
Mild swelling or redness at the site of implant for up to a week or two
Temporary changes in behaviour or appetite
Weight gain and coat changes are occasionally reported with long-term use
In rare cases, the implant may fall out or move from the original location
Long-term hormone use in females (for heat suppression) carries additional risks, including uterine infections, weight gain, and changes in mood or metabolism.
Read more: Signs you should be thinking about neutering your dog
How much is chemical castration for dogs UK?
Costs vary by clinic and the type of treatment, but here are typical prices for the UK, including consultation fee and procedure:
4.7mg implant (6-month): £150-£200
9.4mg implant (12-month): £300–£450
Always check with your local practice for the most accurate cost. It's worth noting that most dogs tolerate the microchip-sized implant without the need for sedation. However, if sedation is needed, the bill is likely to be higher.
Where can you get it done in the UK?
Chemical castration is available at many UK veterinary practices. You can use our Find a Vet tool to check for clinics near you. Give your local practice a call to ask if they offer the implant and whether you can register with them. If they don’t currently provide the service, they may be able to refer you to a nearby clinic that does.
What age can dogs have chemical castration?
Chemical castration is generally recommended for male dogs who have reached sexual maturity (usually around six to nine months). The implant has not been assessed for use in pre-pubertal male dogs. For temporary implants, timing can be important, especially if you're considering breeding later on or managing behaviours as they develop. Always speak to your vet to decide the right age based on your dog’s breed, size and overall health.
Does chemical castration affect behaviour?
Chemical castration can help reduce behaviours linked to testosterone, like mounting, roaming, and scent-marking. Many owners see changes within a few weeks of the implant. A study by Trigg et al. (2006) found it also reduced libido and testicle size, especially in younger dogs.
But it’s not a guaranteed fix. Behaviour is complex, and because behaviours such as mounting and marking can all become established habits, some dogs improve, others don’t. In the first couple of weeks, behaviour can even get a bit worse before it gets better. This is known as the “flare phase”. During this time, it’s wise to keep male dogs away from females in heat.
It’s also worth pointing out that chemical castration, just like surgical castration, may not help with fear-based aggression or guarding, and could potentially increase fear-driven behaviours. These need the help of a qualified behaviourist and some consistent training. If you're exploring how behaviour might change after castration, it's also worth reviewing the signs your dog needs to be neutered to understand when neutering may be worth considering.
In female dogs, hormone treatments can delay seasons and reduce male interest. But some may show temporary changes in mood or behaviour, and hormone-related conditions like phantom pregnancy can still occur.
Permanent chemical options (like zinc or calcium injections) don’t always remove testosterone completely, so behaviours like marking or male-to-male tension might stick around. There’s also some evidence that early neutering, chemical or surgical, might raise the risk of anxiety or joint issues, especially in larger breeds. In these cases, it can help to wait until they’re more physically mature.
Every dog is different. That’s why behavioural assessments are becoming more common. Your vet or a behaviourist can help you work out the best timing and approach for your dog. Used well, chemical castration is a useful tool among many. It works best alongside training, a stable routine, and plenty of positive support.
What do other vets say about chemical castration?
A survey involving 411 UK vets explored their attitudes towards canine castration. The findings revealed that 62% of vets routinely recommended surgical neutering for male dogs not intended for breeding. But many vets are also aware of chemical castration as a useful alternative, especially for owners looking for a less permanent option.
In practice, chemical castration is often considered in specific scenarios, including:
Avoiding general anaesthesia in dogs with health risks
Providing a reversible solution for breeding dogs
Offering a trial period to assess behavioural changes before opting for permanent neutering
Managing multi-dog households or environments with both sexes
Addressing certain medical conditions like benign prostatic hyperplasia
Disadvantages of chemical castration in dogs
Chemical castration has lots of benefits, but it’s not perfect. Here are some of the main drawbacks to be aware of:
Implants can cause a temporary testosterone spike before suppression. During this time, behaviours like mounting or marking may get worse before they improve
Chemical methods may reduce testosterone by less than surgery, which cuts hormone levels by over 90%. So, hormone-driven problems like prostate enlargement or scent-marking may continue
In females, because the uterus and ovaries are still there, risks like pyometra (a severe infection) remain, and may even increase with long-term hormone use
Implants only last 6–12 months. If an owner forgets to repeat the treatment or is late for/misses a dose, fertility returns
Temporary implants can cost as much as surgery, especially if repeated
What do scientists say about chemical castration in dogs
Behavioural effects of chemical vs surgical castration
A Dutch study compared behavioural changes in male dogs that were chemically or surgically castrated. Both methods showed reductions in unwanted sexual behaviours and aggression towards other male dogs. In both groups, playfulness often increased, while general aggression and fearfulness stayed the same. Surgical castration had a slightly stronger effect on sexual interest in females. Overall, the study found both approaches to be effective and safe, providing owners with flexibility in how they manage fertility and behaviour.
Swiss military dogs and working ability
A Swiss study looked at whether chemical castration would affect the working ability of military dogs. Using standard training tests, like obedience, protection, search, and city walks, researchers found no difference between chemically castrated dogs and intact males. This means using a temporary implant didn’t impact the dogs’ focus, trainability or performance. For owners considering castration but concerned about behaviour or energy levels, this study showed dogs can still be active, reliable, and happy, even with reduced testosterone.
Calcium chloride injection in stray dogs
A 2024 study from Cairo University tested a single injection of calcium chloride into the testicles of male dogs. Within two weeks, it stopped sperm production completely, reduced testosterone levels, and shrank the size and blood flow of the testes. The dogs showed no serious side effects, and the changes were permanent. However, this method is not yet licensed for use in UK vet practices, and further studies are needed.
Find out more about chemical castration in dogs
Chemical castration is a helpful option for those not ready to commit to surgery, or whose dog isn’t a good candidate for anaesthesia. As always, talk to your vet about the best option for your dog’s health, behaviour, and lifestyle. Members of Pet Health Club receive up to 20% off surgical neutering. You can find your nearest Pet Health Club vet practice using our Find a Vet tool.
Join the club today
Get regular health checks, vaccinations, and more, all included in your plan.
Show references
Alliance for Contraception in Cats & Dogs (ACC&D). (2024). Products and research. Available at: https://www.acc-d.org
BMC Veterinary Research. (2023). Calcium chloride as a female sterilising agent in rats. Available at: https://bmcvetres.biomedcentral.com
DVM360. (2022). Nonsurgical sterilization technique shows promise as safe, effective alternative to castration. Available at: https://www.dvm360.com
Gfrerer, N., Taborsky, M. and Würbel, H. (2018). No evidence for detrimental effect of chemical castration on working ability in Swiss military dogs. Applied Animal Behaviour Science. Available at: https://doi.org/10.1016/j.applanim.2018.10.019
Mohamed, A., Fathi, M., El-Shahat, K.H., Shamaa, A.A., Bahr, M.M. and El-Saied, M.A. (2024). Chemical castration in dogs using calcium chloride: effects on testicular hemodynamics and semen characteristics. BMC Veterinary Research. Available at: https://doi.org/10.1186/s12917-024-04192-2
NOAH Compendium. (2024). Suprelorin 4.7 mg implant for dogs and cats. Available at: https://www.noahcompendium.co.uk
Parsemus Foundation. (2024). Hormone-sparing sterilisation procedures. Available at: https://www.parsemus.org
ResearchGate. (2022). Adverse reactions associated with a non-surgical chemical sterilant in four dogs. Available at: https://www.researchgate.net
Steur, E.R. (2011). Chemical and surgical castration of male dogs: behavioural effects. MSc thesis. Utrecht University. Supervised by Drs. J. de Gier.
Vet Times. (2016). Attitudes to and opinions of dog castration: vet survey results. Available at: https://www.vettimes.co.uk/app/uploads/wp-post-to-pdf-enhanced-cache/1/attitudes-to-and-opinions-of-dog-castration-vet-survey-results.pdf
WSAVA. (2024). Guidelines on non-surgical sterilisation. Available at: https://wsava.org
Medically reviewed by Lizzie Youens, BSc(Hons) BVSc MRCVS
Published on 03/06/2025 • Reviewed on 03/06/2025