Evidence Update- New Review of Medical Marijuana Research

I have addressed the question of medical marijuana and the use of other cannabis-derived medicinal products twice before. My conclusion in 2013 was this:

The current research evidence supports a couple of uses in humans, including treatment of nausea and poor appetite and possibly pain. Most other uses are poorly supported by clinical research. And there are unquestionably side effects that make marijuana often less useful than isolated cannabinoids or other unrelated treatments.

There is virtually no useful research evidence in companion animals, so any use of cannabis products is based entirely on theory and extrapolation from the limited research results in humans. Canna-Pet as a specific product, is being marketed with very dramatic and aggressive claims about safety and efficacy that do not appear to be supported by specific research on the product but, again, are based entirely on theory and anecdote, both notoriously unreliable sources of evidence.

There are recognized behavioral and medical risks associated with marijuana use in humans. While the behavioral risks do not apply to use in companion animals, and the medical issues associated with THC do not apply to products with negligible amounts of this compound, the risks of cannabis-derived compounds in dogs and cats are largely unknown. Any use of such products, then, should be undertaken with a clear understanding of the high levels of uncertainty about the results, and claims should not be made for these products that go beyond the available evidence.

When I looked again in 2016, I found no further research in veterinary patients, and the basic bottom line had not changed. We often must extrapolate from research in humans to clinical practice in veterinary medicine because we often don’t have the research we need in our own patients to guide us. This is necessary, but it is also risky. Humans are not dogs or cats, and while there are many similarities in basic physiology and in disease and response to treatment, there are also critical differences. The ibuprofen or sugarless gum that is safe for us will easily kill our pets. And the problems with blood lipids and cardiovascular disease that are a major source of human suffering and death are virtually non-existent in our canine and feline companions. So we must also be aware of the risks of leaping from evidence in humans to evidence in veterinary patients even when we have no choice but to make such a leap.

In the case of marijuana and other cannabis-derived products, there is still effectively no research on the risks and benefits in companion animals. Unfortunately, this has not stopped an explosion of marketing of cannabis products to pet owners, with no testing or regulation to ensure safety and efficacy. This is a dangerous situation. The evidence of risks and benefits in humans can help us to some extent to guess at the effects in companion animals, though unfortunately we cannot know how accurate these guesses will be without doing the careful work of rigorously studying these products in the actual species in which we are thinking about using them.

As for the human evidence, on that front there is some good news. The stigma that has hampered research for so long is waning, which is beginning to open the doors to researchers investigating the real effects of the many compounds found in cannabis. And a new review has just been produced which clearly and comprehensively summarizes the existing evidence, making it a lot easy to see the potential risks and benefits that we should focus on investigating in dogs and cats.

The National Academies of Sciences, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research (2017)

This review does the valuable work of comprehensively searching the research literature and then grading the strength of evidence for specific uses. Here is the grading scale the report uses:

Conclusive Evidence
For this level of evidence, there are many supportive findings from good-quality studies with no credible opposing findings. A firm conclusion can be made, and the limitations to the evidence, including chance, bias, and confounding factors, can be ruled out with reasonable confidence.

Substantial Evidence
For this level of evidence, there are several supportive findings from good-quality studies with very few or no credible opposing findings. A firm conclusion can be made, but minor limitations, including chance, bias, and confounding factors cannot be ruled out with reasonable confidence.

Moderate Evidence
For this level of evidence, there are several supportive findings from good- to fair-quality
studies with very few or no credible opposing findings. A general conclusion can be made, but limitations, including chance, bias, and confounding factors cannot be ruled out with reasonable confidence.

Limited Evidence
For this level of evidence, there are supportive findings from good- to fair-quality studies with most favoring one conclusion. A conclusion can be made, but there is significant uncertainty due to chance, bias, and confounding factors.

No or Insufficient Evidence
For this level of evidence, there are mixed findings, a single poor study or health endpoint has not been studied at all. No conclusion can be made because of substantial uncertainty due to chance, bias, and confounding factors.

This is a reasonable and fairly user-friendly scheme for categorizing the strength of the research evidence for or against specific proposed risks and benefits. The summary of the study lists the specific risks or benefits that were reviewed and classified according to this scheme. The benefits and risks are divided into several categories. There are too many to list here, but I will highlight those for which the evidence is at moderate or better and which might be relevant to veterinary patients (meaning, I will skip uses of cannabis for diseases not seen in dogs and cats or risks, such as auto accidents or risks from smoking marijuana, which obviously don’t apply to these species.)

Therapeutic Benefits:
Treatment of chronic pain in adults (cannabis)
Treatment of chemotherapy-induced nausea and vomiting (oral cannabinoids)

Lower birth weight with maternal use
Impairment of cognition, including learning, memory and attention with acute use
Variable increase in risk of development or in symptomatic worsening of various psychiatric disorders (relevance to behavior problems in veterinary patients?)

That’s pretty much it. There are plenty of other risks and benefits with at least moderate evidence that appear only to be relevant to humans. And there are many risks and benefits which could be relevant to veterinary patients but for which the evidence in humans is weak or insufficient to draw any conclusions. And, as I keep pointing out, there is virtually no evidence for any of the many different products out there that directly evaluates risks and benefits of those products in dogs and cats.

So right now, we are at a place where the hype and the marketing far exceed the real evidence that cannabis-based products are safe and useful for our pets. Using them could be worthwhile, but currently it is essentially rolling the dice, an uncontrolled individual experiment that could also make the patient’s life worse. Hopefully, further research will elucidate the real harms and benefits for our pets so we can make sound decisions about the appropriate role of cannabis-based products in veterinary care.




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17 Responses to Evidence Update- New Review of Medical Marijuana Research

  1. anja hunter says:

    I just discovered your website. I love it! Thank You

    From your fellow skeptic Dr Hunter

  2. DL says:

    Thanks for your blog! I’m a pet owner, and I’ve noticed that a number of local vets are into various practices that I’m sceptical of. (I’m from Canada; that’s how we spell sceptic.) Despite my doubts, I just tried hemp oil for my dog’s chronic rhinitis; no effect. Back to proven Western meds.
    It was great to see you quoting the Cochrane folks! Carry on!

  3. DL says:

    PS – I got the idea for trying the hemp oil from Dr. Silver’s website, not from my vet.

  4. Marzena says:

    My heart is broken. I have a very sick kitty. She is 13-14 years old, and whole her life she was vomiting more than she should (now I know that). In February she started to vomit a lot and went from 8.5lb July 2016 to 7.3lb. My Vet prescribed Prednisone, and first month it worked great. But in April we had a decline. In my despair, I went to another doctor for a second opinion, it happened to be a holistic one, she told me to wean off Pred and gave me Nux Vomnica drops. I’m huge fan of Science-Based Medicine Blog, and if it was me sick I wouldn’t even blink my eye and told that doctor that it is huge BS. But this is my baby, I thought that I will go crazy, and was seriously investigating her recommendations. Fortunately reason prevailed, I kept my regular vet recommendations. The natural doctor acted so casually without any need for urgency and it gave me the false sense of security. I know should go to my regular vet right away instead the natural one, since my Kitty’s condition declined within a week. When I went with her 2 weeks ago, she lost additional 0.8lb. She got IV, Cernia injection. I got Cernia and pain meds for home. Mostly it is a comfort care, we have to stabilize her, additional testing was not recommended by my vet for now, until she improves. I’m preparing for the worst, so I had to do my research, how to help her with her disease, how and when to let go… as well. So I decided to check if SBM has anything about pet-healthcare, and I found this wonderful resource of knowledge. It has been really helpful, and I would like to thank the authors and contributors for all their work. The next thing is, that I read this week was that comprehensive study about marijuana usage in humans. I found out that there is strong evidence in humans for chronic pain (I know that my Kitty is in pain), nausea, vomiting. She also gets Mirtazapine for appetite, she is very picky right now. Not to lie, I probably have tried around 50 different can/dry/raw cat foods, for 3 days she ate and enjoyed Fancy Feast Gravy Lovers, but now it is over now, I try to put some nipcat on her food as well, worked yesterday today not so much. So I thought, since most meds that she takes are used in humans, let me check if pot might be for her. Of course, most links from google top search, are not science based. Again I thought I will check this blog, maybe something about pet use marijuana will be here. I was not disappointed, really great skeptical review. But since I’m an emotional wreck right now, I want to ask you, if in my Kitty’s situation you might try to risk the use of pet marijuana supplement products? Is it reasonable to try it? It is always risks vs benefits, and I really want to be sure that I did everything I could to make her life better till the end.

  5. skeptvet says:

    I’m sorry you are facing this situation. Unfortunately, the best I can say is that we really have no idea if cannabis-based products will help you kitty or make her feel worse. Cats are VERY different from humans in how they handle chemical compounds, which makes extrapolation about medicines much more difficult that for dogs. I would expect products with THC to be very likely to have negative effects. Non-THC cannabis products might be safer, but again they are a roll of the dice at best.

    Good luck!

  6. v.t. says:

    Marzena, what is your kitty’s specific health condition? If you haven’t had diagnostics to determine that, you don’t know if there are possible medications to help.

    Sometimes, especially in very ill kitties, it is better to eat something, rather than nothing. Fancy Feast is usually tolerable to most cats, but if she has a gastrointestinal issue, perhaps a prescribed diet for intestinal health could be considered (add a bit of water to canned food, for example, for additional moisture)

    Your vet also has pain medication available if he has determined that inflammation and pain are evident – pain in pets should never go unaddressed (don’t use anything at home, ever – only your vet can prescribe safe and effective pain control for cats’ specific needs).

    Please speak to your vet in greater detail and discuss the available palliative medications that may help your kitty, tolerable foods, fluid support, pain control etc – ideally though, you have to have an understanding of her specific condition in order to treat most effectively.

    Hope she’s feeling better soon.

  7. Marzena says:

    Thank you very much for the responses.

    We don’t have full diagnosis, only elimination; no diabetics, thyroid, kidney, and a few other that my vet mentioned, and I don’t remember. She had all the blood work done. Everything was in norm, except “spec fPL” increased, so definitely IBD, and probably cancer, but no confirmation. Last time she had cholesterol and glucose low, but she was not eating. For now, my vet advised to wait few weeks before ultrasound. When it comes to feeding, that what I was advised by my vet, and this what I’m doing. Whatever she eats she gets, Fancy Feast Gravy Lovers worked for 3 days – she ate 10 cans, and I was ecstatic, I went to buy the whole case but she doesn’t want it anymore. Now she eats Innova Evo dry food, and canned tuna. I’m at pet stores 3 times per week, and have whole cabinet of food that she doesn’t want to eat, and my other cat is getting obese :). I got some prescription food from my vet, she won’t eat that as well.

    I have pain med for her Buprenorphine. I talk to my vet every other day – she probably has enough of me. Except food (she eats what she wants), and Pedisure when I don’t see she is drinking enough, everything I give her is prescribed by my vet and I keep that regiment. Currently we have:
    Prednisolone 5mg/daily, per discussion with vet we switched from Prednisone 2 weeks ago
    Cernia ½ pll/every other day, decreased form daily
    Mirtazapine 1.8mg/every other day, or as needed (not more for sure)
    Buprenorphine every 8-12 hours/ or as needed, but not more often, we are trying do decrease
    If she will be better in few weeks we will do the ultrasound and if it’s cancer we can add some chemo-pills.

    Before I would try medical marijuana on my cat, I would first discuss that with my vet. I would have to find something with CBD, but doing some research, most stuff available is hemp oil with dubious content of CBD. At this stage, preferably if I knew about some legitimate clinical trials on cats, I would go with that. I realize that my Kitty could be in the control group, but it might help some other pets in the future. I will talk to my vet anyway and see what she thinks. I don’t have a high hopes though.

    I simply go crazy, because it is hard to tell when a cat is in pain, and the hardest part when to decide to let them go… Obviously curing her would be preferable…

  8. v.t. says:

    Marzena, it looks like your vet is doing everything right, but perhaps consider the ultrasound sooner because it may show something obvious that treatment could be started promptly.

    Sometimes, pancreatitis and IBD go hand in hand, it might be helpful to ask your vet about subcutaneous fluid support as an added measure. Pepcid AC can also help with an upset stomach from frequent vomiting (please ask vet, since you’re already giving Cerenia).

    Fancy Feast also makes broth packets, you can pour/mix into her canned food for palatability. You could also try cooked white meat chicken (boiled or broiled, nothing added) as a tempter. If she has occasional constipation (i.e, IBD), try a small amount of Laxatone or hairball remedy mixed in canned food, most cats love the taste – even if she doesn’t have constipation, it can be helpful as a tempter in food.

    I personally think marijuana/CBD is not without risk and harm, and particularly, there is no research to determine adverse effects when other medications are also used. Most importantly, it doesn’t “cure” anything.

    I’m hoping for all the best for your kitty, hang in there!

  9. Marzena says:

    v.t. Thank you for the valuable information.

    We will do the ultrasound as soon we see that she is improving and we can put her through additional stress related to it. Next week I should get her weight at the vet’s office and we will see if we have any progress.

    Two weeks ago she got subcutaneous fluids at the vet’s, but I will keep this in mind. For now she is not dehydrated, when I see she is not drinking I will give her Pediasure with a syringe. Due to side effect of Prednisolone she mostly drinks by herself, although I often see her hunching over her water bowl, then I give her pain med.

    I will talk to my vet about Pepcid AC, actually after Prednisolone she has lots of stomach growling. I spoke with my vet about it, but she said that it’s most likely due to her not eating. And when she was eating for those 3 days, her stomach was growling much less. I also asked my vet if Prednisolone might cause her more belly pain, she said it is not likely.

    Laxatone, is a great idea. I will go to Petco and buy it today, since for the past 2 days she eats only dry food and canned tuna. Actually I made tuna soup, she mostly licks water from the can, so I blended tuna with more water and she seems to enjoy it, at least for now. She doesn’t like Fancy Feast anymore, event catnip on it won’t convince her to eat. Yesterday I put under her nose several different kinds of can food, Gravy Lovers, with and without catnip on it, no luck. I even try to heat it up a little in a microwave for the aroma. Then I gave her tuna, oh she licked the whole water, so I blended chunks with water, and finally she ate. I will try to do the same with chicken, I will cook some and blend with water, maybe she will like it. Oh, I also tried baby food; chicken, tuna, beef (no garlic, onion, etc.). I tried Fancy Feast and other broths as well. Every other day I go to pet store, buy few different cans of food and try on her, nothing really works consistently.

    I gave up the idea of giving my cat marijuana/CBD. It was my initial emotional thought when I read about report form National Academies of Science, that for humans there is strong evidence marijuana works for nausea, appetite. At this stage it would not be rational to give it to her. Even if there were some evidence that it works for cats, there is no quality product with CBD that I can buy.

    My main goal here is for her to have a quality life, it doesn’t matter if she has 1 day or 10 years ahead. I would love to have her with me happy and healthy forever, but it is impossible. That’s why I cannot look when she is vomiting and not eating.

  10. Marzena says:

    Just an update, my Kitty is doing great. I will write my ordeal below, but first I would like to point out to anyone that is seeking help for their pet that this is only a story, not a scientific data. I hope that it might give strength to someone that has a sick furry-baby, to trust real doctors and not to get fooled by “medical woo-woo” and alternative medicine.

    Mid May I started a detailed pet diary, since our memory is not always the most reliable. We sometimes tend to mix up and forget stuff, and I wanted to for our doctor to have the most accurate data possible. I tried to write down at least twice a day and track: vomiting, stool, medication – and reactions to them, eating, pain, grooming, walks (yes, I leash-walked her, I went through a list “Aging Cats and Saying Goodbye”), her sleep pattern, play and petting – when her belly was growling a lot, I massaged it to stimulate bowel movement, not sure if it helped but she seemed to enjoy it.

    We did small adjustments, changed from Prednisone to Prednisolone. Doctor said that we could add Pepcid AC, but Kitty is bad with her meds, once she gets pill she will salivate profusely and try to spit it. We tried Laxatone, she is not liking it. Beginning June all she was eating was very little of canned human tuna and few dry kibbles. We tried dozens of cat foods with no luck. I started to give her a little bit of butter for the extra calories, before she was never fond of it, but slowly she warmed up to it to the point that I started giving it to her with pills, especially Prednisolone, so she wouldn’t spit it. She prefers cat food in gravy, so we tried Friskies, Gravy Lovers, 9 Lives, everything that is in sauce. Than I found cat food: Nutro Max Cat in Sauce, they have variety of chicken, turkey, etc.. She started to lick the sauce, and then few chunks. They have small cans, we don’t like to waste food, especially meat, that was a living creature too. With the small can my other cat could finish it without my guilty conscience. He should be on diet, he weighs 16lb, and the Doctor said he that it would be healthy for him to be around 14lb. It is crazy. How to juggle two cats, one that needs to eat and the other that should slim down? Should I become stay-at-home-cat-mommy? 😉

    4th of July weekend was bad she was vomiting and clearly in pain (hunching a lot), although that might me thirst from steroids. I was going to spend time with family, but ended up driving back and forth to keep her on schedule with meds, and to accompany her. Around July 6th, things slowly started turning around. For the first few days I didn’t even put much attention to it. Several times she had a few good days since she got sick, but nothing constant. I didn’t want to get my hopes high. Than days turned to weeks, there was less vomiting. Regularly we went to the doctor for her weight check, and it slowly went up.

    Middle August we went for her checkup and her weight was 9.65lb. We re-checked her “spec fPL” and it is in normal range, all her blood work was in normal range, except thyroid on the borderline below high, but the Doctor said “right now it is not our greatest concern, but we should keep an eye on it”. We haven’t done the ultrasound. Regularly we adjust her meds. She is off Buprenorphine and Mirtazapine for a month and a half. Now we slowly weaning off Cerenia. She will stay on Prednisolone for quite some time, possibly for the rest of her life. I report to our Doctor systematically. We are not out of the woods.

    She begs for food constantly now. 6AM I cannot go to pee, first I have to feed her. Coming from work, she is waiting next to her food bowl, and she is fed the whole day. We are cutting butter – only with pills, because now she loves it. We are laughing that she will have to go on diet soon :). She vomited few times end of July beginning of August, since then only once last Friday, we went for few hours, when I came back and feed her she ate too much too fast and throw up with food. But it was first time in a month.

    Anyone who has a sick pet, just keep talking to your Vet, they are a pet owners too, and they care. Voice any of your concerns, get a second opinion. But be careful, there are plenty of alternative vets who will try to treat your baby with homeopathy or other unproven methods. It is all about odds, and you are increasing their chances of survival by sticking to the science, that is the fact. Not everyone will be us lucky as us. I realize that sooner or later I will have to say goodbye to my babies, but I rather have to do it later, and science helps me to achieve this goal. Or at least to keep my furry babies quality of life on a decent level. Very few people try to control pain with homeopathy, because it doesn’t block pain, why would I want that for my pet, the last thing I want for them is to suffer. Medical marijuana for pets? – Sure, when there are studies that it helps them.

    I wrote my Doctor 5 stars reviews on google and facebook, the only thing that is left, I have to write down a warning (1 or 2 star review) on the holistic doctor’s site. The one that advised to treat her with Nux Vomica. She is a very nice lady, and it is hard for me to do that, but I have a feeling that I need to warn others.
    Also we would like to Thank You and anyone who is contributing to this blog. In the internet jungle of alternative medicine facts and quacks it is much appreciated.

  11. v.t. says:


    I am thrilled to hear your kitty is doing so much better, you must be doing something right! I think you should know, that if your vet felt a pancreatic episode was an issue back in May, sometimes, it can take a cat months to recover completely, other cats may have intermittent/chronic episodes (please watch for those signs!: vomiting, with or without diarrhea, lethargy, inappetence, possibly fever or possibly lower than normal body temperature, obvious abdominal pain/hunched stance).

    For those cats, and possibly your kitty, perhaps feeding smaller but more frequent meals could help, if you’re not already doing so. There is also a theory that giving prednisolone at bedtime (if you’re only giving one dose a day) may help rather than in the morning. Please speak to your vet however, before or if you change her feeding/medication routines, as you certainly don’t want to rock that boat if she is doing well with her current routine.

    I’m glad you’ve taken the time to peruse the information skeptvet has provided on his blog as well as other reputable information. It’s easy for desperate pet owners to go on the way side with woo, but ultimately, when there are effective and safe treatment methods available (and oftentimes, tincture of time and giving the treatment a chance to work), your pets benefit – as opposed to so much uncertainty and potential harm with woo.

    Keep doing what you’re doing, here’s to many more happy and healthy years for your kitty!

  12. Pingback: Cannabis products for dogs? - YorkieTalk.com Forums - Yorkshire Terrier Community

  13. jk says:


    I love this blog and check it often. I got something about this product from a friend via email and posted a link to a press release above. You can delete this post as necessary. Thanks for all your writing, time and assistance.

  14. skeptvet says:

    Bold claims, but since no actual information or evidence has been made public yet, no way to tell what it means. The press release doesn’t really make sense since it says the study was a “pharmacokinetics study,” but then says dogs getting the treatment showed improvement over dogs on placebo, which would be a clinical trial, not a pharmacokinetics study. Anyway, let us know if more info comes out about this research.

  15. greg says:

    It appears cbd oil is all the rage now. There appears to be a battle going on in California between the veterinary board and the alternative practitioners in relation to these products.

    Is there anything new in terms of research relating to companion animals?

    Thank you

  16. skeptvet says:

    Not yet, but there are a number of studies in progress and at least one that has reportedly been completed but not yet published. A lot of information is likely in the near future. For now, I recently posted the slides and summary of a presentation I gave yesterday on the subject.

  17. JK says:

    This is all I’ve been able to find in terms of a follow up to that Cornell info from the PR Newswire (and of course all sorts of places using it to promote their products, which were not looked at) https://ellevetsciences.com/pages/for-vets so that’s not much. Thanks again for this blog!

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