Fact Check: Do LH Levels After Desexing Affect Health?

Updated March 26, 2021

Have you ever wondered why vets recommend one drug over another?

We’ve usually researched it ourselves.

Or we have a wealth of first-hand experience.

However, sometimes the health claims are just too complex to easily assess. That’s when we might trust the company data. But how many vets have the time to double check what they say?

I’ve made a reputation as a ‘difficult’ customer, and I know I’m not alone. That’s because there’s often more than one way to look at the same data. Here’s just one example from the past week: a good product sold by nice people.

Just possibly pushed too far.

The Medical Castration Option

Virbac is a multinational pharmaceutical company selling a product called Suprelorin®. It’s a long-acting implant that blocks the pituitary gland from making Luteinizing Hormone. Which all sounds quite random until you learn that LH is the hormone which tells the testicles to make testosterone.

Dogs given Suprelorin have in effect been given a chemical castration until the implant wears off. That has been great for:

  • Dogs too risky to anaesthetise
  • Old dogs with testosterone-related health problems such as prostatic enlargement
  • Trialling the effects of desexing
  • Owners wanting to keep a male appearance
  • Possibly reversible desexing (only use the 6 month version for this as return to full fertility can be very slow)

It’s also been great for certain chickens and ferrets, but that’s another story. What it hasn’t been great for is places where irreversible desexing is compulsory, like South Australia.

So far, so straightforward. Except now Virbac are claiming that there might be health problems caused by regular desexing that only Suprelorin can solve. You can read the information they gave vets here.

Here I’m going to take an independent look at their claims. You’ll learn a lot more about:

  • The health effects of desexing and
  • How drugs get marketed to vets

First I need you to hang on for a minute while I explain what it’s all about.

The LH Question

A big difference between surgical and medical castration is the blood level of LH. The lack of feedback after castration results in LH levels 30 times higher than before. Suprelorin, by contrast, blocks the pituitary so LH levels are actually lower than normal.

There’s no debate about this. The real question is whether LH is harmful when it’s so high.

Luteinizing Hormone & Dog Health

Here’s the claim: “There is mounting evidence of complications associated with surgical desexing that may be associated with LH receptor activation.” The idea here is that many organs in the body are sensitive to LH levels.

I’ll go through these ‘complications’ one by one and assess the evidence. If they look familiar, it’s because you’ve already seen them on our page discussing the pros and cons of desexing.

But before going any further, I need to point out something vital. Whether or not these problems are caused by neutering, not one of them has been proven to be caused by high LH levels. In fact, for most it’s a stronger argument to blame the lack of testosterone.

So unless you want an update on the health effects of desexing male dogs, you could just skip straight to my rant at the end.


It might come as a shock to hear that several cancers are more common in castrated dogs. However it’s not as bad as it sounds.

It is stated that cancer of the prostate and bladder are both more likely in desexed male dogs. This is a true claim supported by many studies..

On the other hand, claiming that the risk of lymphoma is increased is misleading. In fact, if you read the first study they quote it actually found no difference between sexually intact and neutered males1. Virbac’s other evidence comes from two sources: a small study of Vizslas2, and a higher incidence seen only in Golden Retrievers desexed under one year of age3. Both are too specific to be useful.

The same applies to mast cell tumours: the higher reported incidence has only been documented in the Vizsla study. A larger study4 found that spayed females, but not males, have an increased risk. Virbac are steering dangerously close to what we call cherrypicking here.

Bone cancer does appear more common in neutered dogs5,6, though we don’t have any data on the sexes separately. However, the second study that looked at lifespan also found that the desexed dogs lived longer.

This is the silver lining. Studies that include lifespan consistently point to a longer life for desexed dogs. That’s why we don’t get too alarmed by increases in specific cancers.

Hormonal Disorders

A low thyroid level, or hypothyroidism, has been documented in neutered male dogs7. However, not in the study referenced by Virbac. The industry consensus is best expressed here8: “currently, there is insufficient support for an association between gonadectomy and an increased risk of hypothyroidism in dogs.”

We’re on even shakier ground with adrenal problems. One paper reported a weak effect not separated by sex9, whereas the largest study to date found no link10. An argument used by Virbac is the clear link between adrenal disease and desexing in ferrets. This is faulty reasoning; the hormone involved in ferrets is not the same.

Diabetes is a lot clearer. I agree that neutered males are at a higher risk of developing diabetes11. Of course, the claim goes further to implicate LH levels but here I am doubtful. It is much more likely to be related to the higher rate of obesity in neutered males*.

Joint Problems

Virbac quote a study showing an increased rate of hip and cruciate disorders in desexed male dogs12. This is true, but a series of more recent studies have made it clear that the risk reduces to ‘entire’ rates just by delaying desexing.

So I won’t to do more here than point you to our page on the link between desexing and joint problems.

Behaviour Problems

Virbac claim that desexing increases aggression. I have covered the link between desexing and male dog aggression here. My summary is that there is a clear benefit when we look at the most serious forms of aggression but not when we group all forms of aggression together.

Two studies support the claim that cognitive dysfunction syndrome is more common13 or progresses faster14 in neutered dogs. Having read these papers, I agree, but cautiously, owing to the longer lifespan of desexed males. The differences aren’t alarming but deserve to be studied further.

Urinary Stones

Virbac quote an American trade publication, not really a journal the way we think of them, in support of the statement that neutered dogs get more bladder and kidney stones. The data is unrefined, unanalysed, does not pretend to give answers, and even the author isn’t convinced.

“In this data set the prevalence of urolithiasis was lower in intact male and female dogs and cats, possibly because many of the intact animals were also younger in age.” Gregory Grauer15.

Naturally, other more rigorous studies do not support the statement by Virbac.


I don’t need to quote study after study showing the strong link between neutering and excessive weight. This is clearly true, but its cause is poorly understood. Virbac’s claim that a high LH may affect the appetite actually makes sense to me.

I would love to see some studies comparing the weight and appetite of dogs neutered surgically and medically. This would be wonderful evidence to have. If I could tell an owner that their dog will be less hungry with Suprelorin, it will sell like hotcakes (are you hearing this Virbac?)

Over To You, Big Pharma

This brings me to my final point. When they do it well, pharmaceutical companies provide incalculable benefits to our pets. However, they also have financial interests in promoting their drugs that could get in the way of a clear and frank discussion.

More research is urgently needed to support some of the claims being made about Suprelorin. Your dog deserves better than to be a test subject for unproven assertions.

This is by no means a problem unique to this drug; it’s just the one I chose to highlight. I could point to tens or even hundreds of animal treatments whose evidence base is flimsier. If vets don’t view these critically, it might lead to worse outcomes for your pets.

Despite sounding negative, I actually like the product. It works and it seems extremely safe, if a little expensive. I just don’t like you getting only one side of the story. So thank you for spending the time to hear mine too!

Have something to add? Comments (if open) will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.

Related: A Comparison Of Castration, Vasectomy & Suprelorin | How To Read Science


  1. Villamil, J. A., Henry, C. J., Hahn, A. W., Bryan, J. N., Tyler, J. W., & Caldwell, C. W. (2009). Hormonal and sex impact on the epidemiology of canine lymphoma. Journal of cancer epidemiology2009.
  2. Zink, M. C., Farhoody, P., Elser, S. E., Ruffini, L. D., Gibbons, T. A., & Rieger, R. H. (2014). Evaluation of the risk and age of onset of cancer and behavioral disorders in gonadectomized Vizslas. Journal of the American Veterinary Medical Association244(3), 309-319.
  3. de la Riva, G. T., Hart, B. L., Farver, T. B., Oberbauer, A. M., Messam, L. L. M., Willits, N., & Hart, L. A. (2013). Neutering dogs: effects on joint disorders and cancers in golden retrievers. PloS one8(2), e55937.
  4. White, C. R., Hohenhaus, A. E., Kelsey, J., & Procter-Gray, E. (2011). Cutaneous MCTs: associations with spay/neuter status, breed, body size, and phylogenetic cluster. Journal of the American Animal Hospital Association47(3), 210-216.
  5. Ru, G., Terracini, B., & Glickman, L. T. (1998). Host related risk factors for canine osteosarcoma. The Veterinary Journal156(1), 31-39.
  6. Cooley, D. M., Beranek, B. C., Schlittler, D. L., Glickman, N. W., Glickman, L. T., & Waters, D. J. (2002). Endogenous gonadal hormone exposure and bone sarcoma risk. Cancer Epidemiology and Prevention Biomarkers11(11), 1434-1440
  7. Panciera, D. L. (1994). Hypothyroidism in dogs: 66 cases (1987-1992). Journal of the American Veterinary Medical Association204(5), 761-767.
  8. Houlihan, K. E. (2017). A literature review on the welfare implications of gonadectomy of dogs. Journal of the American Veterinary Medical Association250(10), 1155-1166. [HTML] 
  9. Hoffman, J. M., Lourenço, B. N., Promislow, D. E. L., & Creevy, K. E. (2018). Canine hyperadrenocorticism associations with signalment, selected comorbidities and mortality within North American veterinary teaching hospitals. Journal of Small Animal Practice59(11), 681-690.
  10. O’Neill, D. G., Scudder, C., Faire, J. M., Church, D. B., McGreevy, P. D., Thomson, P. C., & Broadbelt, D. C. (2016). Epidemiology of hyperadrenocorticism among 210,824 dogs attending primary‐care veterinary practices in the UK from 2009 to 2014. Journal of Small Animal Practice57(7), 365-373.
  11. Guptill, L., Glickman, L., & Glickman, N. (2003). Time trends and risk factors for diabetes mellitus in dogs: analysis of veterinary medical data base records (1970–1999). The Veterinary Journal165(3), 240-247.
  12. Witsberger, T. H., Villamil, J. A., Schultz, L. G., Hahn, A. W., & Cook, J. L. (2008). Prevalence of and risk factors for hip dysplasia and cranial cruciate ligament deficiency in dogs. Journal of the American Veterinary Medical Association232(12), 1818-1824.
  13. Azkona, G., García‐Belenguer, S., Chacón, G., Rosado, B., León, M., & Palacio, J. (2009). Prevalence and risk factors of behavioural changes associated with age‐related cognitive impairment in geriatric dogs. Journal of Small Animal Practice, 50(2), 87-91.
  14. Hart, B. L. (2001). Effect of gonadectomy on subsequent development of age-related cognitive impairment in dogs. Journal of the American Veterinary Medical Association, 219(1), 51-56.
  15. Bartges, J. W., & Callens, A. J. (2015). Urolithiasis. Veterinary Clinics: Small Animal Practice45(4), 747-768.

* More on desexing and diabetes: what is interesting here is that when the weight of dogs with diabetes is studied, it is not higher than dogs without diabetes. However, as any vet knows, by the time the diagnosis is made, the dog that was overweight has typically lost a lot of body condition. In fact, it’s our number one suspicion when there’s sudden loss of weight in a persistently overweight dog.

2 Replies to “Fact Check: Do LH Levels After Desexing Affect Health?”

  1. Oh my goodness – this is a brilliant post. It was fascinating to the end and I don’t have entire dogs so the drug isn’t even going to come up on my radar. Can I request more of these analyses of drugs please?
    Also on a somewhat childish side note – is it really called a gonadectomy?

    1. Thanks Judy, and yes, gonadectomy is not only the correct gender-neutral term, but also probably quite funny.

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