Marijuana & Veterinary Medicine

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Marijuana, derived from the cannabis plant, has long been used in human medicine, but its effects on companion animals have only been noted since the mid-to-late 1900s.

When medical marijuana first became legal for human use in California in 1996,1 it was only a matter of time before human patients, pleased with the results of therapeutic cannabis, began giving it to pets with similar conditions.


A 2012 study evaluating 125 client-owned dogs in Colorado presented for known or suspected marijuana toxicosis2 found a significant correlation between the number of people registered for medical marijuana licenses (which had increased 146-fold in the previous 5 years) and marijuana toxicosis cases in animals (which had increased 4-fold), although the study reported only 2 deaths from the “ingestion of baked goods made with medical grade tetrahydrocannabinol butter.”

Marijuana & Hemp

The term Cannabis sativa—the genus and species that comprise subspecies of both marijuana and hemp—is often incorrectly used, so distinguishing between the 2 plants, as well as an intermediate variety, can be difficult. (See Definitions, in Marijuana Toxicity section.) Each plant has many chemical constituents known as cannabinoids, including delta-9-tetrahydrocannabinol (THC), which is psychoactive, and cannabidiol (CBD), which is not.3 

The cannabinoid THC is the most recognized because it is the principal psychoactive component of the plant, but it is one of many, according to the US Pharmacopeia: “The potential for therapeutic activity of cannabis is not limited to cannabinoids; emerging research suggests that other minor compounds … also play a role in the complex pharmacology of this botanical.”3

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The roots of medicinal cannabis have been entwined with human history for millennia, perhaps starting with the Chinese emperor Fu Hsi around 2900 BC.4

Its use next can be traced from the 9th- and 10th-century Arab world, to Europe and Asia in the Middle Ages, to America, where it arrived with early settlers of Jamestown, Virginia, in 1611.4 

Marijuana joined mainstream medicine in the West in the 1840s, when French psychiatrist Jacques-Joseph Moreau discovered it “suppressed headaches, increased appetites, and aided people to sleep.”4

In America, marijuana was added to the US Pharmacopeia in 1850.4

“We are walking a tightrope.”—Tina Wismer

Legal Restrictions

Restrictions on cannabis use began in the early 20th century, with prohibitionists similar to those who later outlawed alcohol. Massachusetts made marijuana illegal in 1911; 10 other states followed suit from 1915 through 1927. When marijuana was removed from the US Pharmacopeia in 1942, it lost what the American Medical Association called its “remaining mantle of therapeutic legitimacy.”4 In 1970, the Controlled Substances Act classified “marijuana (cannabis)” as a drug with “no accepted medical use.” Still today it is listed in Schedule I along with heroin, peyote, LSD, and Ecstasy.5

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Even veterinarians enthusiastic about the benefits they believe these products provide their patients are cautious when discussing them with clients because of legal risks and undetermined therapeutic and toxic dosages. Federal law prohibits veterinarians from prescribing marijuana, even in the 24 states and the District of Columbia where it is currently legal for human medicinal use.6 Hemp-derived supplements are legally available from pet product retailers but are not FDA-regulated. 

Related Article: Do Clients Abuse Their Pet's Prescriptions?

Research: Needed but Complicated

Researchers exploring the potential benefits and risks of cannabis for pets must navigate a legal labyrinth.

“The biggest single issue in the use of marijuana in pets is the legal issue—the fact that it’s still a Schedule I drug,”1 said Robert Silver, DVM, MS, CVA. (See Definitions, in Marijuana Toxicity section.) 

“States are legalizing the use of medical and recreational marijuana. Federal efforts have limited funding for the use of enforcing medical marijuana laws (Congress) or use prosecutorial discretion to limit the enforcement of marijuana laws (Department of Justice). However, those moves do not resolve the serious disconnects in the law that extend far beyond a medical marijuana patient fearing prosecution.

“Both CBD and THC products can have healthful benefits but we don’t know the therapeutic dose. … A pharmaceutical company or large pet food company with a lot of financial resources needs to get these products on the market,” said Tina Wismer, DVM, DABVT, DABT, but to do this they must apply to the FDA. 

If marijuana is declassified as a Schedule I drug on the human side, as some politicians are pushing for, Wismer said, it will become easier to do research. In January 2015, the American Academy of Pediatrics recommended that the DEA reclassify marijuana so more research can be conducted in the hopes of finding benefits for children.2 

Bills aiming to reform marijuana laws and allow further research are pending in both houses of Congress. The Senate bill also reclassifies marijuana from Schedule I to Schedule II and excludes CBD from the definition of marijuana.3,4 

But until the laws change, Wismer said, “We are walking a tightrope.”—Suzanne Smither


Clearly, more research is needed, but obstacles stand in the way. (See Research: Needed but Complicated). Veterinary professionals need to know what is legal and illegal in their state and make the legal status clear to clients when discussing marijuana’s possible benefits for patients.


Therapeutic use of cannabis in pets is a hot topic.

Here are some veterinarians’ views:

Robert Silver, DVM, MS, CVA
“There is a huge body of evidence from well-performed research studies showing … the medicinal value of the whole marijuana plant.”

Narda Robinson, DVM, DO, MS, DABMA, FAAMA
“THC and cannabis in general have anti-inflammatory effects,” she said. According to a survey she conducted, possible therapeutic uses of cannabis also include easing pain, alleviating separation anxiety and seizures, and stimulating the appetites of cancer patients undergoing chemotherapy. 

Related Article: Hybrid Practice Models: Traditional & Non-Traditional Veterinary Medicine

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“I don’t underestimate the therapeutic effects of marijuana. We as veterinarians need to be very cautious because we don’t know the toxic dose; we don’t know the therapeutic dose; and we don’t know the variable amounts of cannabinoids within different products, both hemp and marijuana.”

Tina Wismer, DVM, DABVT, DABT
“When animals eat marijuana, they are going to be symptomatic for a much longer time than humans … 24 to 72 hours. It’s all about the dose.”

“If people have (cannabis) products in their homes, they need to make sure to keep them away from children and pets because they can’t control the dosage.”

Marijuana Toxicity

Clinical Case Summary

Lucy, a 27 lb, 4-year-old spayed beagle, presented with acute-onset lethargy, ataxia, and urinary incontinence. She had vomited once earlier that day, but that was not unusual because, her owners said, she “eats everything.” On physical examination, Lucy was mildly disoriented and hyper-reactive to stimuli (ie, she startled easily, overreacted to hand movements) but was dull when unstimulated and fell asleep. The remainder of her physical examination was within normal limits.

Because Lucy had been unsupervised for several hours before onset of clinical signs, and given her abnormal neurologic status, her owners were asked whether any neurologic toxins (eg, ethanol, ethylene glycol, ivermectin, marijuana, medications [antidepressants, benzodiazepines, barbiturates, opioids, phenothiazines]) were present in the home. The clients told the veterinary team Lucy may have had access to medical marijuana. 

Related Article: Educating New Pet Parents About Poison Prevention


Humans use marijuana (Cannabis sativa) medicinally as an antiemetic and appetite stimulant, and for glaucoma to decrease intraocular pressure, as well as recreationally.1 However, even though the plant has been legalized in some states for medicinal or recreational use, marijuana is still a Schedule I controlled substance under the US Controlled Substances Act.2 (See Definitions.)


  • Cannabidiol (CBD): A crystalline diphenol C21H28(OH)2 obtained from the hemp plant and is nonpsychoactive.1,2  
  • Cannabinoid: Any of the various chemical constituents (such as THC) of cannabis or marijuana.1 
  • Cannabis: 1) A genus of annual herbs (family Moraceae) that have leaves with 3 to 7 elongate leaflets and pistillate flowers in spikes along the leafy erect stems and that include hemp (Cannabis sativa); 2) any of the preparations (eg, marijuana, hashish) or chemicals (eg, THC) that are derived from hemp and are psychoactive.1
  • Hemp: A tall, widely cultivated Asian herb of the genus Cannabis (C sativa) with strong, woody fiber used especially for cordage, as well as a source of psychoactive drugs such as marijuana or hashish.1
  • Marijuana: The dried leaves and flowering tops of the pistillate hemp plant that yield THC and are typically smoked for their intoxicating effect.1
  • Schedule I Controlled Substances: Substances defined by the US Department of Justice Drug Enforcement Administration as those having “no currently accepted medical use in the United States, a lack of accepted safety for use under medical supervision, and a high potential for abuse.”3
  • Tetrahydrocannabinol (THC): The chemical responsible for most of marijuana’s psychoactive effects. THC, one of many compounds found in the resin secreted by the plant’s glands, attaches to receptors in certain areas of the brain, activates them, and affects a person’s memory, pleasure, movements, thinking, concentration, coordination, and sensory and time perception.2

Marijuana’s toxicity mostly comes from a resin called delta-9-tetrahydrocannabinol (THC), but the plant also contains other cannabinoids and cannabinols. 

Ingesting marijuana plant material intended for human consumption via inhalation used to be the most common pet exposure, but now that marijuana has been legalized, it is increasingly available in various forms, including dried plant leaves, edibles (eg, cookies, brownies), butters, and concentrates (eg, oils, waxes). Many edibles include chocolate, which can lead to concurrent methylxanthine toxicosis. Selective breeding of marijuana plants has favored increased THC concentrations—the University of Mississippi Potency Monitoring Project reported that THC levels have more than doubled over the last 25 years.3 THC concentrations vary: for example, plant materials contain 1% to 8%, extracts contain 28%, and hash oil contains up to 50% THC.4 

Whom do you contact if a pet has suspected marijuana toxicosis?

The most common clinical signs following marijuana ingestion are lethargy, depression, ataxia, and urinary incontinence—the latter is unique to dogs and caused by THC metabolites that are not produced during human metabolism. Approximately 25% of patients may display hyperexcitability rather than dull mentation. Other common signs include disorientation, hyperesthesia, tremors, bradycardia, hypothermia, and mydriasis. Patients ingesting high THC doses in concentrates or butter products may display more severe neurologic and cardiovascular signs, including coma and hypotension. Clinical signs may be seen 30 minutes following ingestion and last up to 72 hours.

Diagnosis is typically made based on history of possible exposure and clinical signs. A human urine drug test can be used, but it has not been validated in dogs. False negative results are common in dogs, which produce different metabolites than humans.5 When evaluating these patients, diagnostic tests are essential to rule out ethylene glycol toxicosis because antifreeze poisoning in its initial stages can appear clinically similar to marijuana toxicity. Failure to diagnose ethylene glycol toxicosis routinely leads to fatal acute kidney injury. 


Marijuana toxicosis is rarely fatal because the drug has a wide safety margin, but patients’ cardiovascular and neurologic status, respiratory function, and body temperature should be closely monitored. Only 2 deaths have been reported to date.6

Marijuana is an antiemetic so inducing emesis likely will be unsuccessful but may be attempted using apomorphine within 30 minutes of oral exposure if the animal is asymptomatic. However, apomorphine does not always work because THC affects the vomiting center; hydrogen peroxide, a local irritant, may work best. Also, THC is highly lipophilic and enterohepatically recirculated; therefore, repeated activated charcoal dosing is sometimes used to decrease the half-life of THC in the body7 but should be reserved only for life-threatening situations.

Recovery from marijuana toxicosis may take 24 hours to several days, depending on the amount ingested.

Patients with few symptoms likely will recover with minimal supportive care, but intravenous lipid emulsion should be used in more symptomatic patients to hasten THC elimination, although recovery may be variable.  The dosing regime is a 1.5 ml/kg initial bolus over 20 to 30 minutes followed by a CRI of 0.25 ml/kg/min for 30 to 60 minutes.8 If the response is inadequate, the 1-hour CRI can be repeated once in 4 hours provided there is no lipemia.

Intravenous fluid administration can be used to correct hypotension or dehydration as warranted. Benzodiazepines or low-dose acepromazine are appropriate sedatives for agitated patients if hypotension is absent. Patients benefit from maintaining normothermia, minimizing sensory stimuli, and providing recumbent nursing care if nonambulatory. 

Recovery may take 24 hours to several days, depending on the amount ingested.7 


Lucy was prescribed IV fluids and monitored overnight for declining neurologic status. She experienced mild hypotension that a fluid bolus easily reversed and was discharged the following afternoon with full resolution of clinical signs. 

Related Article: Top 5 Indications for Fluid Therapy

Marijuana toxicosis is being seen more frequently in veterinary medicine,6 with more than 700* marijuana-related calls to the ASPCA Animal Poison Control Center in 2015. Whether this is due to an actual increase in cases, owners’ changing attitudes making them more willing to seek veterinary care, or owners seeking medical attention because their pets are ingesting more potent forms of marijuana is not known. 


Obtaining an accurate history may be difficult when a patient is suspected of illicit drug exposure. (See Questions for a Helpful History.) However, it also is important, so use direct, nonthreatening questions when talking to clients.

Related Article: Solving the Case by Creating a History Together: Part 2

Questions for a Helpful History

An accurate history is most important when a patient is suspected of marijuana toxicity. Ask questions like the following:

  • Is it possible your pet had access to any neurologic toxins such as … while you were gone?
  • Can you describe the clinical signs that made you seek veterinary help?
  • Could any visitors have left marijuana or other medications in your home?
  • Do you have any anxiety medications or antidepressants in your home?
  • Do you have any baked goods or other food items that may contain marijuana?

*From the author, the ASPCA Animal Poison Control Center medical director.

Team Drug Policy

As veterinarians face the prospect of using cannabis or cannabis components in their patient treatment protocols, practice managers need to have a plan in place to deal with team member use of the substance. 

Some states have legalized the Class 1 Controlled Substance, some allow its use for medical purposes only, and others still have not made the drug legal. However, every practice, no matter its location or number of team members, should have a written drug and alcohol policy. (See Resource.)


Safety is Key

Every veterinary employer must provide a safe work environment for team members, clients, and patients, and a policy addressing drug and alcohol impairment will help ensure the workplace is safe. For example, if a team member is taking a prescribed controlled substance but cannot perform his or her job safely and efficiently, the practice is protected so long as a drug policy is in place. (See Drug Policy Example.)

Related Article: Top 5 Items Every Policy Manual Should Include

Drug Policy Example

Following is an example of a drug policy that includes cannabis that is appropriate for a veterinary practice:

VTB Veterinary Practice has vital interests in ensuring a safe, healthy, efficient working environment for every team member, our clients, and our patients. The use or possession of alcohol or other intoxicating drugs in the practice presents a danger to all; therefore, we have established the following Intoxicants in the Workplace policy as a condition of hiring and employment with the practice.

Controlled substances, because of their psychoactive effects, are defined by federal and state governments to describe 5 drug levels, with Schedule I drugs (eg, heroin, LSD, cannabis) the most restrictive and illegal to possess or use and schedule V drugs (eg, cough syrup, sleep aids) the least restrictive and usually available without prescription.

Team members are prohibited from reporting to work or working while under the influence of alcohol and/or other drugs that adversely affect their ability to safely perform their duties.

The practice understands the difference between substance use and substance abuse and that use may not mean abuse. Team members are free to make lifestyle choices when not in the practice or working outside but representing the practice; however, their choices must not interfere with job performance.

Team members are prohibited from reporting for duty or remaining on duty under the influence of alcohol or any other intoxicants. They are also prohibited from consuming alcohol or other intoxicants during working hours, including meal and break periods.

Failure to comply with the foregoing substance abuse policy may result in disciplinary action, up to and including termination of employment.

For more information, please speak with a member of the management team.2

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Different States

Most importantly, be familiar with the varying state laws. According to the Drug Enforcement Agency, marijuana is classified as a Class 1 Controlled Substance and is illegal in all states. However, some states have passed laws that contradict the federal classification and legalize the substance for medical and/or recreational use. A clearly defined practice drug policy is imperative. 

Map of marijuana legality

View Interactive Map
Recreational & Medical UsePermission to grow, possess, and consume marijuana
Medical UsePermission to consume cannabis with a physician's recommendation
Cannabidiol Use OnlyPermission for medical use only of cannabis products that contain a small amount of THC, the psychoactive compound in cannabis
No Laws

In states where marijuana is legalized, the practice policy should state that alcohol and marijuana use will be treated the same way: It is unacceptable to come to work under the influence of either. Alcohol is also legal, but it is illegal to drive under the influence.  

In states where medical marijuana use is approved, a team member does not have automatic permission to be actively under the influence at work. However, accommodations under the Americans with Disabilities Act may be necessary depending on the nature of the job and the safety required.1

Also, the federal Occupational Safety and Health Administration is likely to step in if a marijuana incident occurs in the practice, and the federal illegal status of the drug will likely trump state law.2 (See The Different States of Legal Marijuana, above.)

Implementing a Policy

A drug testing policy should be in writing and include the testing reason (eg, preemployment, random, postincident) and the consequences of a positive test. Be sure to:

  • Fully explain the policy to the team.
  • Apply the policy consistently to all team members to avoid discrimination charges.
  • Document all testing, including the selection method. (See Drug Testing Recommendations.)

Related Article: Drug Testing in a Veterinary Practice: Tester Beware

Drug Testing Recommendations

  • Using a state laboratory that employs a Medical Records Officer (MRO) is the best way to perform any drug testing for the practice, in the author’s opinion. An MRO can interpret the results, compare positive results with a team member’s current prescriptions, and verify the prescription as the reason the team member tested positive. 
  • Testing saliva or blood can estimate recent cannabis use by detecting the presence of THC rather than the inert cannabinoid metabolites detected in a urine sample.4 (This is important in states like Colorado where recreational use is legal and a team member who used the drug over the weekend would show up positive on a urine drug test the following week but would not be under the influence.)

If the practice chooses to test team members randomly, attorneys suggest limiting testing to situations with cause3 (ie, when the manager has reasonable suspicion of drug use), or when the team member has been involved in a workplace accident (eg, tripping, slipping, falling; back injury from carrying heavy patients or products; injury from a patient [dog or cat bite, horse or cow kick]).

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Be sure to document the facts—not gossip or rumors—supporting the cause if the practice does decide to test a team member for cause.

If a Drug Free Workplace Policy is implemented, give team members 30 days’ notice and then test every member to avoid discrimination claims. If management suddenly tests 1 team member without a drug testing policy in place, the practice could potentially be sued.

Related Article: Safety Protocols in Practice 


Every veterinary practice must institute a drug and alcohol policy and test team members appropriately and be prepared to discipline or terminate those who screen positive for current use of illegal drugs.1



When marijuana toxicosis is suspected, run diagnostic tests to rule out antifreeze poisoning, which can appear clinically similar in its initial stages.

Management Team:

Develop a written drug testing policy according to your state’s marijuana laws  that includes the testing method and the consequences of a positive test. Make sure every team member is familiar with the policy.

Nursing Team:

Obtaining an accurate history is key for a patient suspected of marijuana toxicity, so ask clients specific, non-threatening questions to get correct information.

Client Care Team:

Be prepared to answer questions and guide clients to bring their pets in for examination if marijuana exposure is a possibility.

References and author information Show

Overview: From People to Pets

  1. Proposition 215: Compassionate Use Act. California Department of Public Health. Accessed April 2016.
  2. Meola SD, Tearney CC, Haas SA, et al. Evaluation of trends in marijuana toxicosis in dogs living in a state with legalized medical marijuana: 125 dogs (2005-2010). JVECC. 2012;22(6):690-696.
  3. Cannabis inflorescence: Standards of identity, analysis, and quality of control. American Herbal Pharmacopoeia. Published 2013. Accessed April 2016.
  4. Historical timeline: History of marijuana as medicine - 2900 BC to present. Published August 2013. Accessed April 2016.
  5. Controlled substance schedules. US Department of Justice. Accessed April 2016.
  6. 24 legal medical marijuana states and DC: Laws, fees, and possession limits. Published November 2015. Accessed April 2016.


Overview: Research: Needed but Complicated

  1. Controlled substance schedules. US Department of Justice. Accessed April 2016.
  2. Silverman E. Pediatricians urge DEA to reclassify medical marijuana to boost research. Wall Street Journal. Published January 2015. Accessed April 2016.
  3. S.683–Compassionate Access, Research Expansion, and Respect States Act of 2015. Accessed April 2016.
  4. HR.1538–CARERS Act of 2015. Accessed April 2016.


Marijuana Toxicity: Why is My Dog Wobbly?

  1. Delgado J. Marijuana. In: Shannon MW, Borron SW, Burns MJ, eds. Haddad and Winchester’s Clinical Management of Poisoning and Drug Overdose. 4th ed.Philadelphia, PA: Saunders Elsevier; 2007;747-754.
  2. Controlled substance schedules. US Department of Justice. Accessed April 2016.
  3. Potency of marijuana seized in the US more than doubles since 1983. University of Mississippi News. Published May 2009. Accessed April 2016.
  4. Marijuana. Truven Health Analytics. Accessed April 2016.
  5. Teitler JB. Evaluation of a human on-site urine multidrug test for emergency use with dogs. JAAHA. 2009;45(2):59-66.
  6. Volmer PA. Recreational drugs. In: Peterson ME, Talcott PA, eds. Small Animal Toxicology. 3rd ed. St. Louis, MO: Elsevier Saunders; 2013;309-334.
  7. Weinberg G. LipidRescue Resuscitation. Accessed April 2016.
  8. Meola SD, Tearney CC, Haas SA, et al. Evaluation of trends in marijuana toxicosis in dogs living in a state with legalized medical marijuana: 125 dogs (2005-2010). JVECC. 2012;22(6):690-6.


Marijuana Toxicity: Definitions

  1. Merriam-Webster Medical Dictionary. Accessed May 2016.
  2. Bradford A. What is THC? Live Science. Accessed May 2016. 
  3. Controlled substance schedules. US Department of Justice.


Team Drug Policy: Every Practice Must Have a Drug Policy

  1. Atterberry REA. Marijuana in the workplace: A hazy issue for employers. Society for Human Resource Management. Published September 2015. Accessed March 2016.
  2. Burke K. Here’s why you need a workplace marijuana policy. MarketWatch. Published October 2015. Accessed March 2016.
  3. Technical assistance for employers: Drug testing of employees. Accessed March 2016.
  4. NORML’s model workplace policy for cannabis. NORML. Accessed March 2016.


Team Drug Policy: The Different States of Legal Marijuana

  1. Loehrke J. Lighting up legally. USA Today. April 2016:8A.




Suzanne Smither

Suzanne Smither has 30 years of journalism, editing, management, and research experience. Her writing has been published in numerous newspapers and periodicals, and she has written 6 books about cats.

FUN FACT: Suzanne was once adopted by a cat during a hurricane, then surprised with 5 adorable kittens. She learned gourmet cooking by bugging chefs for recipes and tips at fine restaurants while a student in France.

Tina Wismer


Tina Wismer, DVM, DABVT, DABT, is medical director of ASPCA Animal Poison Control Center, adjunct instructor at University of Illinois, and a consultant for Veterinary Information Network (VIN). She earned her undergraduate degree from University of Findlay and her DVM from Purdue University. Tina worked in both small animal and emergency practice before joining the ASPCA. She is a diplomate of the American Board of Toxicology and the American Board of Veterinary Toxicology.

FUN FACT: Tina is a master gardener.

Heather Prendergast

RVT, CVPM, SPHR Synergie Consulting, Las Cruces, New Mexico

Heather Prendergast, RVT, CVPM, SPHR, has been in the veterinary industry for more than 20 years, working in small animal practice and as a consultant. She authored the book Front Office Management for the Veterinary Team and lectures nationally on practice management and veterinary nurse-related initiatives.

FUN FACT: Heather drives a customized Harley Davidson Fat Boy when time allows.

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Veterinary Team Brief delivers practical skills for team-based medicine—with clinical strategies for team training, peer-reviewed credibility, concise content, essential training modules, and easy-to-implement protocols. From the publisher of Clinician's Brief.