Marijuana Poisoning in Pets

Filed Under: Dogs, Cats, Pocket Pets, Horses, Poisoning

There's been plenty of debate about whether marijuana is harmful to humans. But it is definitely harmful to your pet.

Marijuana or cannabis, also known as hemp, marihuana, hashish, Mary Jane, grass, reefer, weed or pot is a coarse annual herb that may grow up to six feet tall. The leaves are palmated, compounded with three to seven linear, coarsely dentated leaves. Male plants have small green flowers at the tip while female pants have flowers along the entire length of branch.

Marijuana was originally native to Asia but is now found throughout the world. Marijuana can often be found growing as a weed anywhere in the United States. Often marijuana is cultivated by individuals in the illicit drug trade and is therefore found in out-of-the-way places or as houseplants within homes.

Originally used as a fiber to make rope, marijuana use has evolved and is now used primarily for its hallucinogenic effects. The principal active ingredient of marijuana having a pharmacological effect is delta-9-tetrahydrocannabinol (THC). THC is a psychoactive agent. The amount of THC in a plant varies with the variety of the plant, the sex of the plant, the geographical location in which it is grown, the state of growth the plant is in, and the nature of the growing season. Immature plants or seedlings contain little, if any of the pharmacological ingredient. THC is found in greatest concentration in the female plant at the time at which it flowers.

Marijuana is a schedule 1 controlled substance mostly used by people as an illegal recreational drug. Marijuana is also used as a drug to prevent vomiting (antiemetic) and to increase the appetite of chemotherapy patients. An additional medical use is to decrease intraocular pressure in glaucoma patients. Due to the high potential for abuse and the availability of alternative drugs, marijuana is rarely used for medicinal purposes.

The most common route of exposure to pet animals is oral. Unfortunately, there have been cruelty cases involving smaller animals, such as a cat placed under a large bowl or bucket and someone blowing their used smoke in with the cat, exposing the pet to toxic levels of THC. In dogs, clinical signs develop within 30-90 minutes after ingestion and even faster with smoke. The effects of the THC may last up to 72 hours. The most common clinical signs of toxicosis in the dog include depression, ataxia, bradycardia (slow heart rate), hypothermia (low body temperatures), vocalization, mydriasis (dilated eyes), muscular incoordination, respiratory depression, hypersalivation, vomiting, diarrhea, urinary incontinence, seizures and coma. The most consistent clinical sign in dogs is central nervous depression, usually appearing as if the dog was falling asleep. Additional clinical signs that may be seen include hyperreflexia (exaggeration of the reflexes), hyperesthesia (increased sensation in the nerves of the skin), and nystagmus (rotation of the eyes). It is rare that a lethal dose is taken, although the period of depression may be prolonged.

Diagnosis is based on clinical signs and a history of exposure. Unfortunately due to the illicit nature of the drug, a history of exposure is often not forthcoming. THC is difficult to detect in body fluids because of the low levels at which it is found in plasma. Urine testing early in the course of exposure may help confirm the diagnosis.

In the absence of a history of exposure to marijuana, diagnosis may be confused with exposure to barbiturates or opioid drugs, various poisons, hypoglycemia, or even encephalitis.

When the history of poisoning is forthcoming, the goal is to remove the drug from the digestive tract through the induction of vomiting followed by the use of activated charcoal to prevent absorption. Additional treatment is primarily supportive. Comatose animals are usually treated with IV fluids, treated for the hypothermia and are given valium to control seizures when present.


Fowler, Murray E. DVM. Plant Poisoning in Small Companion Animals. Ralston Purina Company. 1981. pp-35-36.

Kahn, Cynthia, Editor. The Merck Veterinary Manual. Merck and Co., Inc. p. 2540.

Topics: marijuana

Symptoms: hyperesthesia, hyperreflexia, lethargy, nystagmus

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