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Cannabis sativa poisoning in horses is uncommon, but increasing cannabis cultivation and product availability have made accidental exposure more likely for domesticated animals.
Cannabis sativa is an annual herbaceous plant in the Cannabaceae family with a long history of industrial, medicinal, religious, and recreational use. Also known as marijuana, hemp, weed, pot, hashish, Indian hemp, and cannabis, the plant is now widely naturalized in many regions, including the United States and Canada.
Horses may encounter cannabis in pastures, contaminated feed, discarded plant material, smoke, edible preparations, or other human environments. Clinical signs of cannabis toxicosis in horses most often involve the central nervous system and may include lethargy, altered mentation, incoordination, abnormal behavior, and sometimes gastrointestinal signs such as colic.
Prognosis is generally favorable with supportive care, but affected horses can pose safety concerns because neurologic signs may be unpredictable. Cannabis exposure may also have implications for performance horses because of the potential for positive drug testing. Learn how cannabis poisoning can occur in horses, what signs to watch for, and how veterinarians typically approach diagnosis and care.
Cannabis Poisoning in Horses
Cannabis sativa is an aromatic annual herb belonging to the Cannabaceae family. The species is believed to have originated in central Asia and is now widely distributed and naturalized throughout much of the world, including North America. [1][2]
The cannabis species is highly adaptable and may grow in a variety of environmental conditions and soil types. In North America, cannabis may grow as a cultivated crop, ornamental plant, roadside weed, escaped feral population, or homegrown plant for personal use. [1][2]
Populations are commonly encountered in disturbed soils, abandoned lots, roadsides, agricultural land, and unmanaged environments. In some regions of the United States and Canada, hemp has become a relatively common roadside species. [1][2]
The terminology surrounding Cannabis sativa can vary considerably depending on legal, cultural, and agricultural context. The term hemp is generally used for low-THC fiber or industrial varieties, whereas marijuana commonly refers to preparations cultivated for higher psychoactive cannabinoid concentrations.
Despite these distinctions, all forms belong to the same species complex and may contain biologically active cannabinoids. [1]
Cannabis is referred to by many names, with considerable regional and cultural variation. Common North American terms for cannabis include:
- Marijuana
- Weed
- Hemp
- Pot
- Mary Jane
- Grass
- Bud
- Ganja
Cannabinoids
Cannabis contains more than 60 identified cannabinoids, including: [1][3]
- Delta-9-tetrahydrocannabinol (THC)
- Cannabidiol (CBD)
- Cannabinol
- Cannabigerol
- Cannabicyclol
THC is considered the primary psychoactive and toxicologically important component associated with intoxication in horses and other animals. [1][3]
The concentration of THC within a plant varies considerably depending on genetics, environmental conditions, cultivation practices, plant part, storage methods, processing after harvest, and time elapsed between harvesting and use.
This variability makes it difficult to predict toxicity based solely on the quantity of plant material consumed. [1][3]
Table 1. Cannabis poisoning in horses at-a-glance
| Category | Key Information |
|---|---|
| Definition |
|
| Primary Cause |
|
| Common Causes |
|
| Onset |
|
| Symptoms |
|
| Severity |
|
| Treatment |
|
| Recovery Time |
|
| Prognosis |
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| Prevention |
|
Identification
Cannabis sativa is a coarse, upright annual herb with a strong aromatic odor and rough fibrous stems. Mature plants vary substantially in height depending on environmental conditions, cultivation practices, and plant genetics, but may become tall and conspicuous in open growing environments.
Buds
Leaves
Plant
The species is dioecious, meaning male and female flowers develop on separate plants. Male plants typically produce looser, branching flowering structures, while female plants develop denser clusters associated with cannabinoid-rich reproductive tissues. [4][5][6]
Cannabis leaves are the most distinctive identifying characteristic of the plant. They are palmate (flat), compound and generally have five to seven long, narrow leaflets, although leaflet number may vary between cultivars.
The leaflets have sharply serrated margins and pointed tips, giving the leaves a characteristic star-like appearance. Lower leaves are arranged opposite each other on the stem, while upper leaves become more alternate as the plant matures. [1][4]
The stems are rough, fibrous, and herbaceous, contributing historically to the plant’s use in rope and textile production. The plant emits a strong characteristic odor, particularly during flowering and when foliage is crushed or handled. [4][5]
Flowers are relatively small and green. Male flowers occur in loose panicle-like inflorescences adapted for wind pollination, whereas female flowers occur in denser spike-like or clustered arrangements subtended by leafy bracts. Fruits are small oval achenes enclosed within persistent floral structures and contain the highest concentration of psychoactive cannabinoids. [4][5]
Cannabis is most commonly encountered in unmanaged environments, including roadsides, abandoned agricultural areas, uncultivated fields, illegal cultivation sites, compost piles, and occasionally contaminated hay or feed sources.
Table 2. Easily identifiable features of Cannabis sativa
| Plant part | Identifying features |
|---|---|
| Overall plant |
|
| Leaves |
|
| Leaf arrangement |
|
| Stems |
|
| Male flowers |
|
| Female flowers |
|
| Fruits |
|
| Common growing environments |
|
Toxicology of Cannabis
Cannabis contains numerous biologically active compounds known as cannabinoids, with delta-9-tetrahydrocannabinol (THC) considered the most relevant compound associated with intoxication in horses. [3][7]
Other cannabinoids present within the plant include: [3][7]
- Cannabidiol (CBD)
- Cannabinol
- Cannabinolic acid
- Cannabigerol
- Tetrahydrocannabinol isomers
While there is growing interest in potential uses for these compounds, THC remains the primary compound related to central nervous system effects.
The exact mechanism of toxicity has not been fully characterized in horses. Based on information from other species, THC interacts primarily with cannabinoid receptors, particularly CB1 receptors located throughout the central nervous system. Activation of these receptors alters neurotransmission and may disrupt normal neurologic signaling, resulting in changes to mental state, coordination, behavior, and consciousness. [3][7]
In horses, clinical effects are thought to arise predominantly from central nervous system depression, although stimulation and abnormal excitatory behavior may also occur in some cases. Gastrointestinal irritation following ingestion may contribute to signs of abdominal discomfort or colic. [3]
Cannabinoids may be absorbed following ingestion of plant material, edible products, contaminated feed, or inhalation of smoke. Most equine exposures involve ingestion. There is limited information on how cannabinoids move through the body in horses. Based on what is known from other animals, cannabinoids are thought to spread widely into fatty tissues and organs, including the brain, liver, kidneys, and body fat. [3]
Cannabinoids are thought to be broken down mainly by the liver, and some byproducts may enter the brain. The horse’s body likely removes these compounds through urine and manure, although there is still limited information on exactly how this process works in horses.
The onset and severity of clinical signs depend on several factors, including:
- THC concentration
- Plant genetics
- Fresh versus dried plant material
- Route of exposure
- Quantity consumed
- Processing methods
- Presence of edible products or concentrates
Because potency varies substantially between cannabis products and preparations, clinical severity can be difficult to predict based on exposure history alone.
What's your top priority with your horse's health?
What's your top priority with your horse's health?
Symptoms of Cannabis Poisoning in Horses
Clinical signs associated with cannabis intoxication in horses primarily involve the central nervous system, although gastrointestinal abnormalities may also occur. Signs are variable and depend on potency, quantity consumed, route of exposure, and individual sensitivity.
Reported clinical signs include: [1][3][8]
- Lethargy
- Ataxia and incoordination
- Abnormal or unpredictable behavior
- Central nervous system depression
- Hyperexcitability or agitation
- Colic
- Reduced awareness of surroundings
- Weakness
The onset of clinical signs is not well established in horses. Based on information from humans and small animals, effects following ingestion generally develop within approximately 30 minutes to several hours after exposure depending on the form. [1][3][8]
Although cannabis intoxication is rarely fatal in animals, severe lethargy or unsafe neurologic behavior may require veterinary intervention and supportive monitoring.
Table 3. Signs of cannabis poisoning in horses
| Clinical sign | What it may look like | Why it matters |
|---|---|---|
| Depression |
|
|
| Altered mentation |
|
|
| Lethargy |
|
|
| Ataxia or incoordination |
|
|
| Abnormal behavior |
|
|
| Hyperexcitability or agitation |
|
|
| Reduced awareness of surroundings |
|
|
| Weakness |
|
|
| Colic |
|
|
When to Call the Veterinarian
Contact your veterinarian promptly if cannabis exposure is suspected or if a horse develops unexplained neurologic or gastrointestinal signs. Cannabis intoxication can resemble several other conditions, and veterinary evaluation helps determine whether supportive monitoring, diagnostic testing, or treatment is needed.
Call a veterinarian if your horse shows signs of:
- Depression, lethargy, or reduced responsiveness
- Ataxia, stumbling, weakness, or difficulty standing
- Disorientation or reduced awareness of surroundings
- Agitation, hyperexcitability, or unpredictable behavior that creates a safety risk
- Colic, including pawing, flank watching, restlessness, or reduced appetite
A veterinarian may assess the horse’s neurologic status, hydration, cardiovascular function, gastrointestinal comfort, and exposure history. In some cases, specialized toxicologic testing may be useful, especially for horses subject to regulatory or competition drug testing.
Seek urgent veterinary help if your horse is unable to stand, is severely agitated, appears unsafe to handle, has persistent or worsening colic signs, or may have consumed a high-potency edible or concentrate.
Exposure Risk Factors
Exposure in horses most commonly occurs through accidental ingestion of cannabis plant material, contaminated feed, discarded products, or access to cultivation areas. As legalization and commercial availability of cannabis products increase in some regions, opportunities for accidental equine exposure may also rise.
Potential exposure sources include:
- Discarded marijuana plant material
- Contaminated hay or feed
- Legal or illegal cultivation sites
- Compost piles
- Cannabis edibles or processed products
- Smoke inhalation in enclosed environments
THC concentrations vary substantially between hemp varieties, medicinal products, recreational cannabis, and processed preparations, making risk assessment a challenge. Modern cultivated strains may contain significantly higher THC concentrations than plants grown in the past.
An additional consideration in horses involves drug testing. Cannabinoids and their metabolites may persist within the body for variable periods and could potentially be detected in performance horses after clinical signs have resolved. This has important implications for racing, showing, and other equestrian disciplines, as cannabinoids are on the list of prohibited and controlled substances in most regulated sports.
Cannabis compounds may also interact with other medications, although specific equine drug interaction data are poorly defined.
Diagnosis
Cannabis poisoning is diagnosed mainly by considering whether the horse may have been exposed to cannabis, whether the horse is showing typical nervous system signs, and what is found in the horse’s environment. Veterinarians also need to rule out other possible causes of abnormal behavior or poor coordination.
Inspection of the horse’s environment, pasture, hay supply, or surrounding property may identify likely exposure sources. Signs found during a physical exam can vary depending on how severely the horse is affected, but often include depression, unusual behavior, poor coordination, and signs of digestive discomfort. [3]
Laboratory testing can detect THC or cannabinoid metabolites using specialized toxicologic testing methods such as liquid chromatography-mass spectrometry (LC-MS). Because signs of cannabis toxicosis can also occur with other conditions, veterinarians may consider several possible causes, including: [3]
- Toxic plant ingestion
- Hepatic encephalopathy
- Equine protozoal myeloencephalitis
- Sedative or drug exposure
- Head trauma
- Metabolic disease
- Neurologic disorders
- Colic-associated depression
A diagnosis helps guide treatment, and supportive care is prioritized when cannabis exposure is suspected and the horse is showing abnormal behavior, poor coordination, or signs of distress.
Treatment & Management
There is no specific antidote for cannabis intoxication in horses, and treatment is primarily supportive.
The first treatment priority is removing the exposure source and preventing further ingestion. Contaminated feed, plant material, edible products, or accessible cultivation sites should be secured immediately.
If a horse has recently eaten a large amount of cannabis, a veterinarian may consider gastric lavage or activated charcoal to help reduce absorption from the digestive tract. Most affected horses mainly need close monitoring and supportive care while the body breaks down and removes the cannabinoids.
Supportive treatment may include: [3]
- Monitoring behavior, alertness, and coordination
- Maintaining hydration
- Intravenous fluid therapy
- Providing a quiet and safe environment
- Preventing self-trauma or injury
- Sedation if dangerous agitation occurs
Depression (severe lethargy and dulled responsiveness) is the most commonly reported nervous system sign and often does not require intensive treatment beyond close monitoring and keeping the horse in a safe, quiet environment. Horses that become dangerously excited, agitated, or difficult to handle may need sedation for handler and patient safety.
Intravenous fluids may be beneficial in horses with dehydration, reduced water intake, or prolonged recumbency. Because cannabinoids may interact with anesthetic or sedative medications, elective procedures requiring anesthesia may be delayed in horses exhibiting persistent neurologic abnormalities. [3]
Prognosis
The prognosis for horses with cannabis toxicosis is generally favorable and most recover fully with supportive care. Recovery time depends on exposure route, dose, potency, and individual response. Cannabis intoxication is rarely fatal in animals. [8]
Prevention
Prevention of cannabis intoxication in horses relies primarily on limiting access to cannabis plants, products, contaminated feed, and environments where cultivation or processing occurs. Although equine exposure remains uncommon, the increasing availability and legalization of cannabis products in many regions has increased the potential for accidental intoxication in domestic animals, including horses.
Horses should not have access to cannabis cultivation areas, drying facilities, compost piles, discarded trimmings, or feed storage areas where contamination may occur. Pastures, hay supplies, and feed storage areas should be inspected for contamination with plant material, as feral or escaped Cannabis sativa can grow in many environments.
Prevention is especially important in performance horses because cannabinoids and their metabolites are detectable during drug testing at shows even after the horse has recovered. Even relatively mild or transient exposure may carry regulatory consequences in competitions.
Frequently Asked Questions
Here are some frequently asked questions about cannabis poisoning in horses:
Cannabis can be toxic to horses because it contains biologically active cannabinoids, including delta-9-tetrahydrocannabinol, or THC. THC can affect the central nervous system and may cause depression, altered mentation, incoordination, abnormal behavior, sedation, agitation, and sometimes gastrointestinal signs such as colic. Toxicity may occur after a horse consumes plant material, contaminated feed, edible products, oils, concentrates, composted waste, or discarded cannabis trimmings. The severity depends on the product's potency, the amount consumed, the route of exposure, and the individual horse's response.
If a horse eats marijuana, it may develop neurologic signs such as depression, lethargy, ataxia, weakness, altered awareness, abnormal behavior, reduced responsiveness, agitation, or tremors. Some horses appear unusually quiet or sedated, while others become disoriented, reactive, or unpredictable. Mild gastrointestinal discomfort or colic-like signs can also occur after ingestion. Most affected horses recover with supportive veterinary care, but severe intoxication may require close monitoring to protect both the horse and handlers.
Hemp and marijuana can both be risky for horses because they belong to the same Cannabis sativa species complex and may contain biologically active cannabinoids. Hemp generally refers to low-THC fiber or industrial varieties, while marijuana usually refers to higher-THC preparations, but cannabinoid content can vary widely. THC concentration depends on genetics, plant part, growing conditions, processing, storage, and time after harvest. Horses should not be allowed to eat cannabis plants or products regardless of whether they are described as hemp or marijuana.
Signs of cannabis poisoning in horses most often involve changes in mentation, coordination, and behavior. Affected horses may show depression, lethargy, poor coordination, weakness, reduced awareness of surroundings, abnormal behavior, hyperexcitability, agitation, or colic. Clinical signs vary depending on THC concentration, amount consumed, route of exposure, product type, and individual sensitivity. Any sudden neurologic change should be treated as a veterinary concern because these signs are not specific to cannabis exposure.
Signs after cannabis exposure in horses may appear within about 30 minutes to several hours after ingestion, although the exact onset is not well established in horses. Timing can vary based on the product type, route of exposure, amount consumed, and cannabinoid concentration. Edibles, oils, and concentrates may create different risks than fresh or dried plant material because potency and absorption can vary. A horse with suspected exposure should be monitored closely and assessed by a veterinarian, even if signs are mild at first.
The duration of cannabis effects in horses is not well defined because controlled equine research is limited. Recovery time likely depends on the amount consumed, THC concentration, exposure route, product type, and the individual horse's response. Mild signs may resolve sooner, while exposure to high-potency edibles, concentrates, oils, or large amounts of plant material could cause more prolonged neurologic depression. Cannabinoids and their metabolites may also remain in the body after visible clinical signs improve.
Cannabis poisoning can cause colic-like signs in horses when ingestion irritates the gastrointestinal tract. Affected horses may show abdominal discomfort, restlessness, reduced appetite, or other signs that resemble colic. These signs are not specific to cannabis and can occur with many other medical problems, so exposure history is important. Contact a veterinarian if colic occurs after known or suspected access to cannabis plants, products, contaminated feed, or discarded material.
Cannabis poisoning in horses is rarely considered fatal, but it can still be medically significant. Severe depression, prolonged recumbency, dehydration, agitation, unsafe neurologic behavior, or poor coordination may require veterinary treatment and careful monitoring. The greatest immediate risks are often injury, handler safety, and complications from altered awareness or impaired movement. Prognosis is generally favorable when further exposure is prevented and supportive care is provided.
If your horse ate cannabis, remove the horse from the exposure source and contact a veterinarian for guidance. Secure any plant material, contaminated feed, edibles, oils, concentrates, trimmings, compost, or discarded waste so the horse cannot consume more. Keep the horse in a quiet, safe area and avoid unnecessary handling if it is disoriented, unsteady, sedated, or agitated. Prompt disclosure of possible cannabis exposure helps the veterinarian choose appropriate monitoring and rule out other serious causes of neurologic signs.
You should call a veterinarian for suspected cannabis exposure if a horse shows depression, lethargy, incoordination, weakness, abnormal behavior, agitation, colic, reduced awareness, or any sudden neurologic change. Veterinary guidance is especially important if the horse may have consumed edibles, oils, concentrates, or an unknown amount of plant material. Seek urgent help if the horse cannot stand, is severely agitated, appears unsafe to handle, has persistent or worsening colic, or may have eaten a high-potency product. Even mild signs can create safety risks because affected horses may behave unpredictably.
Cannabis poisoning in horses is diagnosed using exposure history, clinical signs, environmental assessment, and exclusion of other causes of abnormal mentation or ataxia. A veterinarian may ask about access to cannabis plants, discarded products, contaminated feed, smoke, cultivation areas, drying facilities, compost piles, or edible products. Specialized toxicology testing may detect THC or cannabinoid metabolites when confirmation is needed, especially in performance horses. Because the signs can resemble toxic plant ingestion, sedative exposure, head trauma, metabolic disease, neurologic disorders, or colic-associated depression, veterinary evaluation is important.
Cannabis poisoning in horses is treated with supportive care because there is no specific antidote. The first priority is removing the exposure source and preventing further ingestion of plant material, contaminated feed, edibles, oils, concentrates, or waste. Depending on the case, veterinary care may include neurologic monitoring, hydration support, intravenous fluids, a quiet and safe environment, gastric lavage or activated charcoal after recent substantial ingestion, and sedation if dangerous agitation occurs. Most horses recover fully with appropriate monitoring and supportive management.
Horses can be exposed to cannabis through contaminated feed, hay, bedding, compost, discarded plant material, or access to cultivation and drying areas. Accidental incorporation of plant material into forage is possible, especially in regions where cannabis or hemp production is common. Feed rooms, hay storage areas, pastures, compost piles, and unmanaged margins should be inspected for suspicious plant material or contamination. Securing feed sources is important because potency varies widely between cannabis plants and processed products.
Cannabis smoke can expose horses to cannabinoids, but most reported equine exposures are believed to involve ingestion rather than inhalation. Smoke exposure may be a concern in enclosed environments where ventilation is poor or where horses are close to cannabis use or processing. However, a horse showing neurologic signs should not be assumed to have a simple smoke exposure without veterinary assessment. Depression, ataxia, abnormal behavior, or colic-like signs can have many possible causes and should be evaluated promptly.
Cannabis can affect performance horses by impairing coordination, responsiveness, mentation, and normal neurologic function. These effects may reduce athletic performance and create safety concerns for riders, handlers, and other horses. Cannabinoids and their metabolites may remain detectable in blood or urine after clinical signs have resolved. This can create regulatory concerns in racing, showing, and other governed equestrian events where cannabinoid exposure is prohibited.
It is not safe to give cannabis or CBD products to horses unless they are specifically prescribed and supervised by a veterinarian and allowed under applicable regulations. Cannabis products vary widely in cannabinoid concentration, and some may contain THC or other compounds with neurologic effects. Drug interactions and performance testing concerns are also not fully defined in horses. Owners should not assume that cannabis, hemp, CBD, or edible products are harmless simply because they are plant-derived.
Cannabis may grow around horse properties in disturbed soils, roadsides, abandoned lots, agricultural land, unmanaged fields, compost piles, and areas near cultivation sites. In some regions of the United States and Canada, hemp can occur as a roadside or escaped feral plant. Horses may also encounter cannabis through discarded plant material, trimmings, contaminated hay, or feed stored near cultivation and drying areas. Regular inspection of pasture edges, fence lines, feed storage areas, and rough unmanaged spaces can reduce accidental exposure risk.
Horse owners can identify cannabis plants by looking for a coarse, upright annual herb with a strong characteristic odor and rough fibrous stems. The leaves are usually the most recognizable feature: they are palmately compound, often with five to seven long, narrow leaflets, sharply serrated margins, and pointed tips that create a star-like appearance. Female plants develop denser clustered flower structures associated with cannabinoid-rich reproductive tissues, while male flowers are looser and more branching. Any suspicious plant material in turnout areas, hay, feed, compost, or storage spaces should be removed from horse access and identified carefully.
You can help prevent cannabis poisoning in horses by restricting access to cannabis plants, edible products, oils, concentrates, supplements, discarded waste, contaminated feed, and cultivation areas. Store cannabis products securely and keep feed rooms, tack areas, barns, compost piles, pastures, and drying facilities free from discarded or escaped plant material. Horses should not have access to baked goods, concentrates, trimmings, or waste that may contain high levels of THC. Regular inspection of forage, storage areas, and turnout spaces is especially important in regions where cannabis or hemp production is common.
Summary
Cannabis poisoning in horses is a toxic reaction that can occur when a horse ingests or is exposed to Cannabis sativa plants or cannabis-containing products.
- Cannabis poisoning in horses is uncommon but may become more likely as cannabis cultivation and product availability increase
- Horses may be exposed through cannabis plants, contaminated feed, discarded material, edibles, concentrates, smoke, or cultivation areas
- THC is the main toxic compound and primarily affects the central nervous system
- Signs may include lethargy, altered mentation, incoordination, weakness, abnormal behavior, agitation, or colic
- Treatment is mainly supportive and focuses on removing the exposure source, monitoring the horse, maintaining hydration, and providing a safe environment
References
- Thal. D. Hemp Poisoning in Horses. HorseDVM. 2018.
- Orsini. J. A. and Divers. T. J. Eds. Equine Emergencies: Treatment and Procedures. Fourth edition. Elsevier/Saunders, St. Louis, MO. 2014.
- Hovda. L. R. Blackwell’s Five-Minute Veterinary Consult Clinical Companion Equine Toxicology. Wiley Blackwell. 2022.
- Martin. C. G. and Brym. Z. T. Cannabis Sativa Plant Identification and Its Look-Alikes. Ask IFAS. 2024.
- Burrows. G. E. Toxic Plants of North America. 2nd ed. John Wiley & Sons. 2013.
- Hesami. M. et al. Morphological Characterization of Cannabis Sativa L. Throughout Its Complete Life Cycle. Plants. 2023.
- Donaldson. C. W. Marijuana Exposure in Animals. Veterinary Medicine. 2002.
- Fitzgerald. A. H. et al. Marijuana Toxicosis in 2 Donkeys. Journal of Veterinary Diagnostic Investigation. 2022.
