Skip to content
Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

More Melatonin and Dog Cancer

Updated: April 13th, 2021


More details on melatonin and dog cancer, including the whys, hows, and how much.

You want more on melatonin and dog cancer? You just hit the jackpot!

Why Melatonin?

Why should we be interested in this weird body hormone that is only generated in complete darkness?  Lots of reasons.

First of all, melatonin used with chemo versus chemo alone more than doubled the survival time of human cancer patients. That’s a big effect, folks.

Secondly, in that same study, melatonin decreased the side effects related to chemotherapy.  These included low platelet counts, irritations of the lining of the mouth (stomatitis), nervous system injury (neurotoxicity), and heart toxicity (cardiotoxicity).  Again, that is huge.

Listen to this episode of Dog Cancer Answers to find out more about how to use melatonin to fight dog cancer. 

A simple hormone, produced naturally, and also cheaply found in supplement form, is related to doubled survival times and decreased side effects? That’s literally a no-brainer.

But Wait, There’s More:

Melatonin helps overcome weight loss due to cancer (cancer cachexia)  in advanced cancer patients, with no change in how much food they are eating.

As if this were not enough, a study looked at over 600 cancer patients, with a variety of solid-tissue tumors, who received melatonin.  The 1 year survival time of the group that took melatonin was more than a third greater than those that did not.

Melatonin was also the topic of a medical conference which discussed the ability of melatonin to cause some cancer cells to not only die off directly, but go back to being healthy body cells, and decrease cancer spread (metastasis). Let me restate that: melatonin seemed to not only kill cancer cells but in some cells, to turn them BACK TO HEALTHY CELLS.

To boot, melatonin is an immune stimulator.


To put it mildly, there is lots of promising stuff here.  One of the points made at that conference was that this information has been around for years — but has not made it into the medical or veterinary knowledge pool.  (As I pointed out in the last post, I think the obvious reason is that you can’t patent it, which means no pharmaceutical company is interested … but I digress.)

Free Ways to Boost Melatonin

Obviously, dogs produce melatonin at night, in complete darkness, just like humans do. That’s why it’s a good idea to increase your dog’s natural melatonin output — and possibly even supplement it.

First, the free strategies: create a natural “den” for your dog to sleep in. Total darkness, for at least 10 hours daily can be accomplished in many ways:

  • If your dog likes sleeping “under” things, like tables, or beds, let them do it. This is their way of stimulating melatonin, by seeking dark places to snooze.
  • If your dog likes to sleep in a crate, there are fantastic covers that make it super-dark in their little cave.
  • Make your bedroom a den, particularly if your dog sleeps with you. Use blackout shades on your windows, and make sure all sources of “blue light” from TV screens, computers, tablets, and phones are removed. Stop using night lights. Make your room as dark as possible, so your dog’s brain has a real shot at generating melatonin.
  • If you can, avoid charging your devices where you sleep, because electrical fields can interfere with melatonin production. For the same reason, considering unplugging lamps and other devices at night.
  • Try some fresh sage in your dog’s cancer diet — it has lots of naturally occurring melatonin!
  • Other rich sources of melatonin are brown rice and oats, both of which are optional additions to the dog cancer diet outlined in my book.
  • Meditation — yes, meditation — increases melatonin levels. Try meditating with your dog!

Supplementing with Melatonin

Dogs vary in their natural ability to generate melatonin, and they also vary in size. Therefore, melatonin doses vary, too.

If your dog is in the early stages of dog cancer, I recommend using 1-2 mg per 40 lbs body weight, once a day, given at night.

For advanced dog cancer patients closer to the end of their life, I recommend 5 mg per 40 lbs.

You can use either tablet or liquid forms, whatever works best for your dog. Whatever form you choose, give melatonin with a little food to buffer the stomach — just a snack will do it.

I like human-grade supplements because they are manufactured to stricter standards than pet-grade supplements. Melatonin is a really inexpensive supplement, and worth trying with your dog.

Side Effects for Melatonin and Dog Cancer

Here’s the skinny on side effects and whatnot…

  • Don’t give your dog melatonin during the daytime, because it messes up their circadian rhythm and causes headaches. You probably know this firsthand if you’ve ever woken up in the middle of the night and had to turn on the light only to get very groggy and a little sick.
  • Any supplement given by mouth has the potential for digestive upset (vomiting or nausea), of course, which is why I suggest giving with a little food.
  • If your dog has any immune-mediated disease (like some types of underactive thyroid problems, dry eye, lupus, pemphigus, allergies, and so on), avoid it.
  • Don’t give melatonin to your dog if he or she is on calcium channel blockers (some types of heart and blood pressure meds), or is on fluoxetine (Prozac).
  • Because melatonin can influence metabolism, diabetic dogs may need less insulin on melatonin. So if your dog has diabetes, begin melatonin only with your vet’s close supervision and instruction. If you are not willing or able to consult with your veterinarian to manage diabetes medication, please skip melatonin. You don’t want to overdose your dog on insulin unnecessarily!
  • Melatonin being generated by the brain, I would avoid melatonin as well if your dog is epileptic.

There are statements suggesting melatonin should not be used with leukemia or lymphoma patients circulating.  I have tried to find some actual evidence for these (a paper, case report, anything real) but to no avail.  Any input from the readers?

The same is true with this idea that it can cause retinal injury. This appears to be speculation, but I am open to any documented, real evidence.

Best to all,

Dr. Dressler

Leave a Comment

  1. Linda on October 8, 2023 at 4:21 am

    Have you heard more about giving a dog with lymphoma melatonin. It sounds promising but don’t want to comprise if it is contraindicated. Any help is greatly appreciated

  2. Mel on September 14, 2018 at 3:39 am

    Just wanted to note that in humans, SSRIs and melatonin are often used in combination.

    What is the reason you discourage using both in dogs? Would love to know if there is info I am missing. Thanks!

  3. Laurie on October 13, 2011 at 5:49 am

    Hannah, my beautiful 50 lb.,14 year old Siberian Husky has inoperable cancer probably originating on an adrenal gland and atypical Cushing’s. At this point in time, her quality of life is not too bad. An ultrasound suggests the cancer has spread; an X-ray shows a very enlarged liver, blood work shows some very elevated liver enzymes. I am trying to reconcile melatonin dosage recommendations: Cushing’s protocol says 3 mg twice a day; cancer protocol suggests 6 mg. evenings; then I see internet references to melatonin being contraindicated for dogs with liver disease because melatonin is hard on the liver. Help! Hannah has been taking melatonin one month; and I can see its positive effects on her overall well being and functioning, including fur growth; though that is the least of my concerns. What would you do with a dog with a confluence of issues like this? At this point in time she is taking lignans, milk thistle, melatonin, PS, DGB, Wei Qi, a multiple vitamin and may add Stasis Breaker later. Weaned off Metacam and Tramadol; recently had an Adequan series of injections. Trying to give her liver as much of a break as possible; but very aware of melatonin’s cancer fighting properties, not to mention the Cushing’s. She is eating high protein grainless commercial canned and kibble ; laced with chicken breast; although I did give home-cooked a real try. Too many peas and carrots now, I know, but it is the compromise she and I arrived at. For the first time, last night I switched to 6mg melatonin in the evening, but I am worried about it. Should I continue to give her as much as 6 mg, once a day with her stressed liver? Should I give her less? Her vet is as conflicted as I am. What do you think? Thank you so much.

  4. lyn on February 5, 2010 at 2:15 pm

    Beg to differ with the doc but according to Dr Oliver “STEROID PROFILES IN THE DIAGNOSIS OF CANINE ADRENAL DISORDERS” under sub heading melatonin “Also, in dogs with adrenal disease that are treated with melatonin, and repeat adrenal steroid panels are done, cortisol levels are consistently reduced, and estradiol levels are variably reduced.29 Inhibition of the 21-hydroxylase enzyme would lower cortisol levels, and inhibition of the aromatase enzyme would lower estradiol levels. Estradiol levels were decreased in a prior study of dogs treated with melatonin.31 Results of in vitro studies with human MCF-7 breast cancer cells also revealed that melatonin inhibited aromatase enzyme, which resulted in reduced estradiol levels.56 Melatonin treatment for cases of mild adrenal disease in dogs may be effective, and particularly in cases where sex steroids are increased.”

  5. Jane DeBlasio on January 11, 2010 at 10:04 am

    I have a question for Dr. Dressler
    My dog was diagnosed with atypical cushings (pituitary tumor/sex hormone elevation)
    I was told to give 3 mg. of melatonin in the morning and 3 mg. of melatonin at night along with flax. I read your article about the problem with giving melatonin in the daytime. I also spoke with Dr. Oliver from Tennessee who told me that this has been the regimen for atypical cushings for the past 10 years. What is the best way to administer melatonin to my dog? Also, will giving melatonin in the daytime cause health risks for my dog?

    Thank you.

  6. Kristen on September 28, 2009 at 2:33 am

    Dr. Dressler,

    Why do you say avoid melatonin if your dog is epileptic? A lot of canine epilepsy sites recommend it.

    Thank you,

Scroll To Top