Cannabis – a dose of realism?

15th February 2019
Beryl Shuttleworth
6 Responses

cannabis horsesThose of you who know me will know how intensely irritated I am by ‘fads’ in natural medicine. You know what I mean – coconut oil, turmeric and now, Cannabis.

I thought I’d spend this morning putting all things Cannabis into perspective, with special reference (of course) to horses, dogs and cats.


Plants and Molecules

There are three different species of Cannabis – sativa, indica and ruderalis. Ruderalis is seldom grown. Cannabis sativa and indica are very similar and are used both medicinally and recreationally. The main difference between them is their size (indica is shorter). The two main varieties of Cannabis sativa are commonly known as Marijuana and Hemp.

Being a biochemist, I find that the best way to understand medicinal plants is at the molecular level. There are two main molecules in Cannabis plants: THC (tetrahydrocannabinol) and CBD (cannabidiol). THC is the molecule with psychoactive effects (in other words, it makes you ‘high’). CBD has no psychoactive effect. Both THC and CBD have medicinal value.

Mostly, because both of these molecules are fat soluble, oil extracts of Cannabis are used. The table below compares typical levels of THC and CBD in Marijuana (which can be indica or sativa), CBD oil and Hemp oil.

Hemp oil < 0.3% low
CBD oil 1 – 5% 18 – 20%
Marijuana 5 – 40% low


Molecules and Disease

THC and CBD seem to be effective in the following diseases:

Various cancer – breast, glioma, leukaemia,

lung, colon amongst others

Anxiety Nausea and vomiting
Epilepsy Loss of appetite
Inflammation Inflammation


This research has all be done in humans or in vivo (in the test tube), but it has been assumed that the same effects will be seen in animals.


So What’s the Problem?

The problem is that all things Cannabis have suddenly become extremely popular. The oil extracts can be quite potent, yet people are manufacturing these in their homes with no controls in place. Regulatory bodies can’t keep up and while they are researching things like interactions, dosages, safety and side-effects, people continue to use the oils in the meantime. Completely new cannabinoids are being isolated and touted as more effective, etc. Home remedies have limited quality control in place and contaminants in plant based products are common. Products are being sold with misleading information on the labels – a study on actual versus claimed contents showed there is very little correlation.

Then, there are unfortunately, side-effects. THC produces psychoactive effects. Smoking (or passive smoking) of marijuana has been linked to lung cancer. Although CBD oil decreases tumour growth in breast cancer, THC has been shown to increase it. How sure are you that your CBD oil is THC free?


Cannabis is travelling a very thin line between miracle medicine and natural supplement. The diseases we are treating with Cannabis are serious diseases. It makes me nervous when the safety information doesn’t keep up with the feeding frenzy.


Be careful, friends, and always consult your vet.



Hazekamp A: The Trouble with CBD Oil. Med Cannabis Cannabinoids 2018;1:65-72. doi: 10.1159/000489287

Jikomes N, Zoorob M. The Cannabinoid Content of Legal Cannabis in Washington State Varies Systematically Across Testing Facilities and Popular Consumer Products. Sci Rep. 2018;8(1):4519. Published 2018 Mar 14. doi:10.1038/s41598-018-22755-2

Ashton, C. (2001). Pharmacology and effects of cannabis: A brief review. British Journal of Psychiatry, 178(2), 101-106. doi:10.1192/bjp.178.2.101

Blessing EM, Steenkamp MM, Manzanares J, Marmar CR. Cannabidiol as a Potential Treatment for Anxiety Disorders. Neurotherapeutics. 2015;12(4):825-36.

Massi P, Solinas M, Cinquina V, Parolaro D. Cannabidiol as potential anticancer drug. Br J Clin Pharmacol. 2012;75(2):303-12.


6 Responses

  1. Thank you for this article. I was given what was apparently a natural CBD oil to help with my dogs cancer. It changed her personality completely and she attacked one of my other dogs. Now, if I give her CBD, it is from a reputable provider in the US whose oil has gone through rigorous testing, is sans the tHC and has been proven to work well on pets as well. It’s expensive though but I would rather use something that is safe and tested.

  2. Hi. It’s so good to get a bit of a reality check from someone with knowledge about the product. I was hoping you could steer me in the right direction. I have been treating my dog’s mast cell tumour topically with full extract cannabis mixed in coconut oil for about 8 months now. Sometimes I would spray some DMSO on it to help with absorption. While the tumour itself has not grown, the leg has swollen(this already happened before I started the cannabis. It seems to have stopped the cancer from spreading further, but has not done anything to shrink it. She is otherwise in no pain and in such good health, runs like a puppy, eats like a wolf and generally full of the joys of life. Do you think I may get better results using CBD rather than THC?

    1. Ria, that is such awesome news, well done you! And yes, I think you should theoretically get better results from a CBD oil. But remember, as always, every dog is an individual, so keep a close eye on her reaction and stop if there are any problems. I’m super interested in her progress, please keep me updated. And best of luck. 🙂

  3. Hi there
    Found this article very interesting
    I have grown cannabis in my garden with my small veggie garden and would be interested in having it tested to see which plant it is…where could I do this
    Louise Schwob
    Ps can it be used in feeding an older horse

    1. Thanks, Louise. Yes you can use it for old horses.

      I’m not sure where you could get it tested. But, I have heard about a plant identification app which you can download to your phone. Not sure of the name, but its probably worth a try….

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