Chemical Castration in Your Future?

Cactus looking like penis and testicles

You want to do what to my boys?

Chemical Castration

“We can just inject this zinc compound into his testicles, and voilà, no more sperm production! Neutering without the knife!”

A reader asked that I weigh in on Zeuterin, the injectable castration agent made from zinc gluconate. It’s made and marketed by Ark Sciences.

Kind of a cool play on words, you’ve got to admit: Zinc + neuterin’ = Zeuterin. Will it become a new verb? “I took Fritz in to get zeutered yesterday. He’s pretty swollen and sore today.”

Here’s how an injection sterilizes a male dog or cat.

The zinc solution is injected into the body of each testicle. Only those who’ve taken the company’s training can do this, and so far, that’s only veterinarians. The injection is made via a very fine needle, while the dog is sedated but usually awake. Some are not even sedated.

Once inside the testicle, the chemical spreads throughout the gland, creating inflammation and killing sperm. The inflammation is such that the testicles swell for several days, and scar tissue is laid down as a healing response to the chemical insult. This scar tissue effectively closes the tubules that are necessary for sperm maturation and delivery.

No tubules, no sperm production. And zinc is toxic to existing sperm cells, so they die. Chemical neutering is accomplished within minutes and is permanent.

Is It Worth it To Neuter Male Animals?

That ought to be your first question before considering chemical vs. surgical procedures.

As I pointed out earlier, the incidence of several diseases increases after neutering, including hypothyroidism, several kinds of cancer, obesity, and multiple orthopedic problems, including cruciate ligament rupture.

In addition, there’s evidence that neutered (and spayed) animals are significantly more likely to have vaccination adverse events in the first few days post-vaccination. [1. Moore GE, Guptill LF, Ward MP, Glickman NW, Faunt KF, Lewis HB, Glickman LT. Adverse events diagnosed within three days of vaccine administration in dogs. JAVMA Vol 227, No 7, Oct 1, 2005]

Odds are, neutered males will never be a significant birth control measure if animal overpopulation is a concern of yours. A female in heat will draw the unneutered male via her powerful pheromones, even if a population of males is somehow 90% neutered.

Known Side Effects

Zinc gluconate is aggressively irritating to tissue, which is why all the scar tissue forms in the injected testicle. If some of the solution leaks during delivery, scrotal ulcers result, and if enough leaks, a full on surgery may be necessary to remove the scrotum as well as the testicles.

The word “necrotizing” appears in the literature associated with this drug. If it leaks during the procedure, healthy tissue the zinc solution contacts dies. Necrosis is tissue death, and it’s not pretty. The fix is a bigger surgery than a simple neuter would have been.

Ouch! No, Probably Not

Yep, some of these dogs hurt after injection, as you might imagine. The clinical trial data showed a low percentage of this, but there was crying, licking, and general discomfort.

Trial dogs for FDA approval numbered 270, and post injection pain occurred in 17 of them, mostly within the first two days of the injection.

From the company’s literature:

While adverse reactions requiring medical treatment occurred in only 1.1% of the dogs, there were minor reactions observed in 6.3% of dogs during the FDA study. Local reactions included testicular swelling (normal reaction to the injection), pain (dogs may resist sitting or may sit with both hind legs open), biting and licking at the scrotum, swelling of the prepuce and irritation, dermatitis, ulceration, infection, dryness or bruising of the scrotum. Systemic reactions included an increase in the white blood cell count, vomiting, anorexia (loss of appetite), lethargy (tiredness or abnormal attitude), and diarrhea.”

In defense of these findings, odds are, if the technique is done properly (very fine needle, very slow injection into the testicles), this will be a painless procedure. Why?

Nature, in her infinite wisdom, has put different pain receptors in various areas of the body. The testicles, much like the intestines, feel stretching, especially sudden stretching, as painful (think gas pains in the belly here).

As my physiology professor pointed out, a match held under a loop of intestine wouldn’t cause pain. Those pain receptors are in the skin, where they act to keep us away from fire.

Similarly, a testicle has pain sensors for crushing injury or sudden expansion, but not for a chemical “burn,” which is essentially what this drug produces. Likely not to hurt, if (a big “if”) the vet is careful in the injection.

Possible Advantage Over Surgery: Testosterone

One upside of “zeutering” over neutering is that the production of testosterone is not shut down completely. Somehow, the cells of Leydig, responsible for this hormone’s production, are left intact after the injection. Because there’s no longer a chemical signal for more testosterone production by developing sperm cells, the overall production of testosterone drops by about 50%.

Testosterone loss is complete in surgical neutering. It’s like throwing a switch when the surgeon removes gonads. “Instant menopause” for the females, and as one wise crack commenter on Quora called it, “instant man-o-paws” for the males. As I mention in the fuller page on neutering, loss of these hormones is a significant one to the animal and can set them up for ill health.

So, keeping some testosterone in the male is a good thing. One protective role of testosterone is a reduction in prostate cancer in dogs.

Provings in Homeopathy

All the substances used in homeopathy have undergone what are known as “provings.” This is where human volunteers, often doctors, take repeated doses of a remedy to see if it elicits symptoms.

The first known proving and the one that launched homeopathy was Dr. Samuel Hahnemann’s self experiment of taking Peruvian bark, Cinchona. This was the crude source of quinine, the cure for intermittent fever or malaria. Amazingly, in his healthy body appeared symptoms of intermittent fever, quite similar to those experienced by malaria sufferers.

He surmised that substances that are capable of producing symptoms are also capable of curing diseases that produce those same symptoms, and homeopathy was born in 1790.

Zinc: Depressed and Fagged Out

If you look up zincum metallicum in your materia medica, you’ll see a pretty dark picture that’s come from either

  1. people poisoned with excess zinc,
  2. provings dating back to Hahnemann,
  3. or those cured of illness with a homeopathic prescription of zinc

The word “fag” comes: worn out, depressed in function, both physically and mentally. “Marked anemia and profound prostration.” Weakness, restlessness. Convulsive twitching or jerking, worse at night, during sleep (hmm, I see this in a lot of my patients, and interestingly, it goes away when they become cured after proper homeopathic treatment). In big bold print (meaning it was common to many of the sufferers in a zinc state of illness), DEFECTIVE VITALITY.

My own homeopath, perhaps more sensitive to zinc than most, was given zinc lozenges by a friend, and told of the deep depression it put her in, “I wanted to jump off a bridge and end it all!” From the materia medica, “Thinks calmly of death.”

So, zinc is a chemical I’d not want injected into my body, certainly, nor into my patients’ bodies.

Zeuter Your Animal? Nah.

In sum, I don’t see chemical castration as a means to more vital animals. Current long term studies are only 40 dogs, tracked informally for over two years (the maker is quick to point out, “fourteen in human years.”). Not too impressive.

The healthiest, most vital guys in my practice still have their testicles (or ovaries), are fed balanced raw food, are minimally vaccinated, and stay away from toxic pesticides for fleas and heartworm prevention.

Their owners are responsible people. They see to it that males don’t breed and females don’t get pregnant by knowing their animals’ whereabouts and exercising close supervision when they go out.

I suspect shelters who are bent on neutering will find more use for this drug than the average pet owner.

OMG. This Really Exists??

Just for fun, before we part ways this time, in my research for this article, I stumbled across something that left me dumbfounded: Neuticals.

Yes, if you don’t want it to look like your neutered male is, erm, lacking in any way, your surgeon can now implant artificial testicles after he’s done! With the real look and feel of a full scrotum, no one ever need know that your guy isn’t packing any more.

The site actually frames their sales pitch partly around how your dog would feel better, sporting a pair of falsies in his scrotum when he walks down the street! Really?

Amazing. Really speaks to the society we’ve become, where appearances have become so important. Epitomized by Kim Kardashian, featured prominently on the Neuticals website, hanging out of her blouse with her dog Rocky, who’s sporting the latest in surgical technology: phony nuts.

Have you thought about using zinc to neuter a male in your life? Oh, maybe I should rephrase that, in case you and your husband are at odds at the moment. Have you considered using chemical castration for an animal in your pack? Let us know in the comments.

And, if you’ve used Neuticals, well, odds are you’re not reading this but are planning your next bust enhancement or tummy tuck. Probably nothing of interest to you on this site.

Photo Attribution

Print This Article

Click below, press print, and enjoy offline reading.


  1. Margaret Chandler on February 22, 2024 at 9:07 am

    Please could you comment on managing enlarged prostate in senior dogs? Ive used homeopathic remedies for 6 years, but now it’s enlarged again and the vet ( Traditional & Homeopathic) want to neuter. I don’t want to neuter if there is any way to resolve the problem without neutering. I’d like to here your opinion on this.. I do hope you can respond to my question.

    • Will Falconer, DVM on February 23, 2024 at 5:45 am

      This is the definition of chronic disease, and while it’s curable with homeopathy, it’s not likely to be DIY or a “one remedy wonder.” To find a qualified homeopathic vet for this work, here’s how I recommend searching. Key in this: this can be long distance work.

  2. pamela on April 15, 2017 at 9:21 am

    Okay, I’m going to inject a bit of levity here ….. I quit watching TV about 10 yrs ago. Got better things to do with my time. So when people first started talking about the Cardashians I thought it was the aliens from the old Star Trek series! Imagine my surprise a few yrs later while checking out at the grocery store to see a picture of a human Cardashian!

  3. natty on February 13, 2015 at 4:10 pm

    Hi Dr Falconer-
    What is your opinion on vasectomy and ovary sparing spay?

  4. Will Falconer, DVM on January 21, 2015 at 9:20 pm

    Joyce, thanks for checking on the urine drinking. I’m leaning toward hypersexual, too, but if many unneutered males do it, I might hold out and only use that as a symptom if it occurred in a neutered male.
    In the wild, there’d be much less access, soaking into the ground, but yes, maybe someone has studied this. There are certainly groups who study wolf behavior very closely. Let me know if you find anything there. That’d be the measuring stick I’d be most interested in.
    And with that, I’ll talk to you tomorrow!

  5. L on January 21, 2015 at 3:29 am

    I would be concerned that having an unaltered cat or dog that will never be allowed to breed may be stressful for the animal and possibly lead to health problems also. In the wild an animal wouldn’t be celibate.

  6. Hanna on January 15, 2015 at 4:18 pm

    Question –
    I don’t own male dogs (never will for my own reasons). I have always had females and always had them spayed. Yes, I am responsible to NOT let them get pregnant, but I don’t want to deal with heat cycles and the mess.
    Does that make me IRRESPONSIBLE?

  7. Joyce on January 13, 2015 at 11:24 pm

    I am so glad that I did not neuter my male GSD. A few years back I had considered doing it, only after he had matured. But a while back you wrote a good blog about all the issues that could take place. So I changed my mind and I am very happy I kept him in tact, he is 6 years old now.
    I don’t have issues with marking. He does have an intensity about licking my female’s urine, but I have been told that is normal behavior.
    As always, I appreciate your wisdom Dr. Will. Thank you.

    • Will Falconer, DVM on January 14, 2015 at 9:53 am

      Thanks for your input, Joyce.
      I have a patient who drinks urine, and now I know why! I thought it odd, as he was the only one I knew who did this in all these years of practice. Interesting to hear that it’s normal behavior. Have to float a survey to hear how common this is.

      • Joyce on January 14, 2015 at 11:55 am

        Interesting, Dr. Will. Maybe it isn’t so normal after all, considering you have not seen it in your practice but once?
        Of the many folks I know with male dogs, they tell me it’s quite common. Hmmm, I’d like to know more.
        I am over on NCHS ( Natural Canine Health Symposium) Dogs Naturally group. I think I will just pop over there and ask this very question! Thanks for the idea! I will let you know what I find out.
        There are about 500 members, I hope people will answer this inquiry. It’s an easy way to get some answers.

        • Will Falconer, DVM on January 14, 2015 at 5:02 pm

          Sure, see what you find out and come back to let us know. If you have a good Facebook connection or a Twitter bunch, ask around and see what you learn.
          Thanks Joyce.

          • Joyce on January 20, 2015 at 10:16 pm

            I had about 15 responses and it appears very common with intact males, and even a few neutered males as well as a few females that participate in this behavior.
            I found it interesting that Dana Scott had mentioned she believes this to be a hypersexual behavior.
            One common occurrence is the “chattering” that occurs after licking of the female urine, an indication the male is recognizes this is female.
            Reminds me of the National Geographic shows when a male lion wrinkles his nose ( Flehmen response) and opens his mouth when smelling female pheromones. This must be a similar response with intact male dogs especially. I think Dana is right about this being a hypersexual behavior, as there were a few responses (including Dana’s dogs) who do not do this licking behavior.
            All in all, it appears very common. Does make me wonder what the behavior is like with wild coyotes and wolves?

  8. Brooklyn on January 13, 2015 at 10:00 pm

    Hundreds of thousands of homeless dogs and cats are homeless today. Please, please don’t encourage people in any way to not spay/neuter. That’s why we are in this mess in the first place.

  9. Pam on January 13, 2015 at 8:57 am

    You know when a human woman has to have a full hysterectomy and she has to take hormones, because she can no longer produce them?
    Would it not be possible to replace testosterone and hormones for our spayed and neutered dogs in a similar fashion?

    • L on January 13, 2015 at 10:42 am

      Regarding hormone replacement, I would be concerned about the risk of cancer. Possible aggression with testosterone…as noted in humans.

    • Will Falconer, DVM on January 13, 2015 at 7:24 pm

      I suspect replacement therapy is a partial effort at best. Hormones and their interactions with one another is not a simple substitution game.
      But I’m also not well versed in it. I think you’d be better off not removing gonads altogether, for health’s sake.

  10. Cheri Hoffer on January 12, 2015 at 11:21 pm

    Since 1998 I’ve run a dog home boarding business in Colorado. We require spay/neuter status for a well-socialized dog to come stay in one of our homes. Close to ten years ago a client came to my home on a meet-n-greet with a sweet mutt that we’d been told was neutered. Upon slow introductions, the first dog, my own beloved Pug/Norwegian Elkhound-x NM, Pugsley ran up into this dog’s face and yapped at him. Pugsley was a quiet fellow. EVERY direction their dog turned, Pugsley ran in front of him and yapped, but nothing more. That sounding of his little alarm meant that their dog was intact. In our thirteen years together hiking, boarding and traveling he never ever once was wrong. He wasn’t neutered until he was found at about four years old and he knew well the smell of testosterone. When I relayed this to my new clients standing by and confused, they told me over and over that their dog was neutered by the shelter. He had a very bushy double coat obscuring his hindquarters and I had not yet asked him to bend over and cough(!). Finally, their protestation changed and they said he was chemically neutered. Sparing you the rest of the story, dogs still react to the smell of testosterone and while the hormonally intact (to some degree) dog may be totally chill, it sets off some other dogs and raises the tension level in a group. In parks I’ve sometimes seen an intact male surrounded by neutered males, forcing a confrontation. But we must set our Camp dogs up for success, not confrontation. I’ve also found–in early years of the business–that dogs with testosterone are far more likely to mark in our sitters’ lovely homes than neutered males. That urine is far more potent than the urine of neutered males, attracting others to mark over it. There goes the neighborhood!
    The more I read, the more value I see in leaving dogs unaltered surgically. But it’s the rare home boarding business owner who will welcome intact males for reasons already mentioned, but a growing number of people want this level of quiet, highly personal care. Chemical neutering doesn’t seem like the answer, but I see the appeal to underfunded shelters moving hundreds or even thousands of pets through their doors every year. Until your article I had not seen posed the potential threat of zinc in the dog’s body. It’s clear that sooner or later I will have to be prepared to have this conversation with clients. But we won’t be boarding zeutered dogs anytime soon. Thank you.

    • Will Falconer, DVM on January 13, 2015 at 6:12 am

      Interesting, Cheri. Pugsley was a testosterone detector, sounds like!
      And no, probably wouldn’t work for a home boarding situation like you describe, but I’d hope there was a way.
      Thanks for sharing your thoughts.

  11. Roxanna on January 12, 2015 at 5:21 pm

    I have a question regarding intact male dogs. My dog is still intact and several dog trainers that I know have warned me that other dogs, especially male dogs, will sense that mine is still intact and will react more aggressively toward him. Do you find that to be true?

    • Mary Marseglia on January 12, 2015 at 6:26 pm

      Hi Roxanna, I have been a dog trainer for 30yrs and dog & cat behaviorist for 24+yrs and although other males will sense your male as being intact, as long as your male is well socialized and you are the “pack leader” of your dog, you should have no problems. I raised/trained/showed/handled/trained Schutzund for 14yrs before getting a back injury(will be back this year so 19yrs as I have kept up with everything of my Top 100% West German Bloodline show/working GSD’s) and my male stud dog was intact and got along with all other males.
      I only believe in spay/neuter for people who are not going to be responsible or for an animal that actually has a problem physical illness that requires spay/neuter. No we don’t need more puppies & kittens in this world, but I can tell you that in Germany(actually many countries in Europe including the UK) they have 60% of all their dogs intact and they have no problems and they all play in fields and dog parks and regular parks. When a female comes into heat, she is banned from running loose and they are responsible. We here in the US need to take lessons from other countries in Europe especially Germany, and stop doing all this harm to our animals.

    • Will Falconer, DVM on January 12, 2015 at 7:00 pm

      No, Roxanna, I think this is erroneous. The intact males, like any other dog, can sort out social signals given half a lick of socialization in their upbringing. Socialization simply means spending time out in the real world, interacting with all kinds of dogs, cats, people, horses, rain storms, etc. etc.
      I grew up with one intact male dog after another in my home, from age 8 or so till I went off to vet school. I never saw them get in fights or have other dogs treat them aggressively.

  12. Karin on January 12, 2015 at 5:01 pm

    Glad to read all this research, although when I first heard of it in the beginning of the article, my gut told me “NO”. It’s amazing all the weird things we invent to interrupt natural life.
    However, I really would like to read more about neutering and not neutering. Our pup, your patient, is not neutered yet as we agreed with you, that to wait would be better. I figured I wouldn’t even worry about it until he was a year old, which will be in a few months. He is doing great and I don’t want to ruin that. But, I am not too familiar with male puberty. In the past we had our males neutered very early.
    One thing he is doing is any chance he gets, he licks the male genitals of other dogs. I looked this up on the internet and read things about “getting to know” another dog and dominance issues. I would love to hear your take on this and how to limit it, or whether it’s proper to do that. However, it’s upsetting to other people and not the kind of behavior we want to see either. Also, do you do neutering yourself?
    Thanks for your excellent newsletters!

    • Will Falconer, DVM on January 12, 2015 at 7:06 pm

      Hi Karin,
      Sounds like a bit of an overbalanced behavior. In medical terms, perhaps an overly strong sex drive. I had a patient who did this, in Chicago. Bugged the hell out of any male that came to visit. It finally went away as we treated the “whole dog” homeopathically through a few remedies.
      It’s probably best to set a follow up appointment and see if there might be a few symptoms that could guide us to a proper remedy for this randy teenager! Shoot me an email. Likely, we can talk this week.
      I stopped surgeries about 25 years ago when I dove into holistic practice with my whole being. I quickly realized that there were clinic on every corner who could fulfill that need, but not even a homeopathic vet per good sized city.
      Glad you’re enjoying Vital Animal News.

      • Karin on January 14, 2015 at 12:12 pm

        Will set up an appointment soon. Thanks!

  13. Kathi Richards on January 12, 2015 at 4:08 pm

    Great explanation of the zeutering process. ugh.
    I am still up in the air when it comes to s/n. I understand what you are saying Dr Falconer of the health benefits of not doing the procedures, but that, I feel, pertains to “responsible” pet care takers. Sadly there are too many that are not responsible, not even close. Yeah, they shouldn’t have a dog or cat, but they do. They take good care of them but maybe aren’t with them all the time. Maybe they don’t realize the problems that are in the overcrowded shelter. Maybe they felt that is better to let them be and breed with whoever comes by. That is the case here in California for the most part. Ignorant people, and I say that kindly as they really don’t understand. The shelters are killing fields for the most part. Not all, but many. All sorts of reasons for the dogs and cats being there but the bottom line is that a human let it happen, or set it up to happen. Education is happening and s/n is a tool.

Leave a Comment