Sunday, October 13, 2013

Rising Levels of Marijuana Poisonings in Pets

"Did someone say 'cookies?'"
Following up on a previous post on this blog about foods that can be poisonous to pets, I saw an article today from Huffington Post that notes that marijuana poisonings in pets are on the rise, partly due to the increased use of medical marijuana.  Medical marijuana that is put into baked goods or other snacks is an easy way for dogs or cats to quickly ingest a high and potentially toxic dose of the drug.  Dogs don't know the difference between cookies and "special" cookies; it is all the same delicious temptation to them.  Studies have already shown a correlation between increases in the numbers of medical marijuana licenses in certain states and the numbers of marijuana poisonings seen at local vet clinics. 

Let's talk a bit about what marijuana does in the body as well a why medical marijuana is a particular danger to pets.  The goal of this post is not to advocate or criticize medical marijuana (we're not getting into politics), but to just discuss some of the facts and science behind it.     

Though they contain psychoactive chemicals, the leaves of the marijuana (Cannabis) plant are relatively "non-toxic" in terms of their potential to cause death or serious illness.  The minimum toxic oral dose for actual marijuana leaves in dogs is fairly high, around 3 grams per kilogram of body weight.   That's a lot of marijuana leaves; 30 grams (1 oz) for a 10 kg (22 lb) dog.  The fairly high lethal dose also extends to humans, which is why legitimate marijuana overdoses are rare.  Most often, a person will simply fall asleep before ever getting close to ingesting or smoking a lethal dose of pot.  

However, some "medical marijuana" products contain concentrated levels of tetrahydrocannabinol (THC), the main psychoactive ingredient in marijuana.  THC is very lipid (fat) soluble, which is why it is often extracted from marijuana leaves or synthetic sources with fats like butter, and then medical marijuana products can be made from this "THC butter."  That lipid solubility also means that ingested THC can rapidly be absorbed and distributed to various regions of the body where it can stick around for a while. 

Absorbed THC is typically distributed in fat and in other organs, including brain, kidney, and liver.  Clinical signs in dogs can begin in as little as 60 minutes.  Lower doses in dogs can cause depression, lethargy, vomiting, or tremors, while higher doses can cause irregular breathing (tachypnea), heartbeat (tachycardia), or other muscle movements (ataxia).

Anandamide, an endocannabinoid
Many people don't realize that your body makes makes substances that activate cannabinoid receptors that are an important part of human physiology.  These substances are called endocannabinoids (endo means "internal" or "from within") to distinguish them from plant cannabinoids or synthetic cannabinoids.  These endocannabinoids are important signaling molecules in your body.  Cannabinoid molecules acts on at least two different but related receptors, called cannabinoid receptors.  We know of two such receptors, but there are very possibly more than two.  The cannabinoid receptor CB1 is found mainly in the brain, while the CB2 receptor is found in other tissues.  Most of the depressant or hallucinogenic effects of marijuana are thought to be due to the CB1 receptor in the brain.  However, the cannabinoid system and both CB1 and CB2 receptors play a role in many body processes, including mental function, pain, metabolism, and reproduction. 

The effects on metabolism and pain relief is why medical marijuana has been advocated to increase appetite and reduce nausea and pain in cancer patients.  There's a lot of legitimate science behind this, though not all physicians have come to a consensus on the benefits of marijuana vs other conventional drugs.  However, there's enough evidence of marijuana's benefits that many states in the US have decriminalized or even legalized the use of medical marijuana with a legitimate prescription. Despite the fact that the ability to get medical marijuana is often abused by people who don't necessarily need it, medical marijuana has improved the lives of sick people, particularly terminally ill patients with cancer.      

With this increased availability, though, comes an increased need to make sure that it doesn't fall into the wrong hands or paws.   While some vets have experimented with using marijuana to treat sick pets, there's no real research yet on whether or not marijuana has actual benefits for pets.  Anecdotal stories are not the way that physicians or veterinarians make decisions on the efficacy (clinical effectiveness) and safety of drugs.  They need real, rigorous, and properly controlled studies.  Dogs and cats can be poisoned by marijuana, partly because they are often so much smaller than people.  A smaller amount of THC is toxic for them.  With our societies' increased acceptance of marijuana products, we need to educate people to treat medical marijuana products like they would any other prescription medication: keep it away from pets and children to prevent accidental poisonings.   

Sources and Further Reading
  • M. Bostwick.  "Blurred Boundaries: The Therapeutics and Politics of Medical Marijuana."  Mayo Clinic Proceedings.  2012. 87:172-186.  Available here.
  • P.A. Clark, K. Capuzzi, and C. Fick.  "Medical Marijuana: Medical Necessity Versus Political Agenda."  Medical Science Monitor.  2011.  17:RA249-RA261.  Available here.
  • K.T. Fitzgerald, A.C. Bronstein, K.L. Newquist.  "Marijuana Poisoning."  Topics in Companion Animal Medicine.  2013.  28:8-12.
  • I. Grant, J.H. Atkinson, B. Gouaux, and B. Wilsey.  "Medical Marijuana: Clearing Away the Smoke."  Open Neurology Journal. 2012. 6:18-25.  Available here
  • F. Grotenhermen and K. Muller-Vahl.  "The Therapeutic Potential for Cannabis and Cannabinoids."  Deutsches Arzteblatt International.  2012.  109:495-501.  Available here.
  • P. Janczyk, C.W. Donaldson, S. Gwaltney.  "Two Hundred and Thirteen Cases of Marijuana Toxicoses in Dogs."  Veterinary and Human Toxicology.  2004.  46:19-21.   
  • L. Leung.  "Cannabis and its Derivatives: Review of Medical Use."  Journal of the American Board of Family Medicine.  2011.  24:452-462.  Available here
  • R. Mechoilam.  "Cannabis--A Valuable Drug that Deserves Better Treatment."  Mayo Clinic Proceedings.  2012.  87:107-109.  Available here.
  • R. Mechoulam and L.A. Parker.  "The Endocannabinoid System and the Brain."  Annual Reviews in Psychology.  2013.  64:21-47.
  • S.D. Meola, C.C. Tearney, S.A. Haas, T.B. Hackett, E.M. Mazzaferro.  "Evaluation of Trends in Marijuana Toxicosis in Dogs Living in a State with Legalized Medical Marijuana: 125 dogs (2005-2010)."  Journal of Veterinary Emergency and Critical Care.  2012.  22:690-696.
  • R.G. Pertwee.  "Cannabinoid Pharmacology: The First 66 Years."  British Journal of Pharmacology.  2006.  147:S163-171.  Available here
  • P. Robson.  "Therapeutic Aspects of Cannabis and Cannabinoids."  British Journal of Psychiatry.  2001.  178:107-15.  Available here.    


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