In recent years, cannabidiol (CBD) has gained popularity as a natural remedy for some equine medical conditions. Currently, research into the effects of CBD on horses is very limited, and many reports of its purported benefits are anecdotal.
Cannabidiol is a non-psychoactive compound found in cannabis plants. Research in humans and other animals shows that CBD products exert anti-inflammatory, anti-anxiety, anti-depressant and pain-relieving effects.
In horses, CBD supplements are commonly used as a calming aid. They have also been used by horse owners to address lameness, stress and pain from injuries or gut issues, including colitis.
While some of the purported effects of CBD may be borne out in future studies, many claims about the benefits CBD oil for horses are dubious or lack research to evaluate their validity.
Before administering CBD to horses, horse owners should first consult with a veterinarian.
CBD for Horses
Cannabidiol (CBD) is a phytochemical present in the cannabis family of herbaceous, flowering plants. Common strains of cannabis plants include Cannabis sativa and Cannabis indica. 
The cannabis plant produces over 500 naturally occurring and biologically active compounds, many of which are known as cannabinoids. Cannabinoids can be either psychoactive or non-psychoactive. 
CBD is a non-psychoactive cannabinoid. It is the major cannabinoid in the hemp plant, with concentrations varying between different strains. 
In Canada and Europe, CBD and products containing CBD are controlled substances. 
Strains of cannabis are classified as either marijuana or hemp, depending on their concentration of THC (tetrahydrocannabinol).  THC is the most significant cannabinoid found in marijuana plants and is known for its psychoactive properties.
In Canada, the USA, and Europe, hemp (typically Cannabis sativa) is legally defined as any part of the cannabis plant that contains less than or equal to 0.3% THC on a dry weight basis. 
The term marijuana typically refers to parts of the cannabis plant containing more than 0.3% of THC. 
The Endocannabinoid System (ECS)
Cannabidiol influences the endocannabinoid system (ECS), a recently discovered biochemical communication system in vertebrates that influences many physiological functions through a network of chemical signals and cellular receptors. 
The ECS controls functions needed to maintain health, including homeostasis (a state of metabolic balance) . This system also influences:
- Learning and memory
- Emotional processing
- Temperature control
- Pain control
- Inflammatory and immune responses
The ECS is a complex cell signalling network comprised of three major components including: 
- Cannabinoid receptors (CB1 and CB2)
- Endocannabinoids that occur naturally inside the body
- Enzymes required for the synthesis and degradation of endocannabinoids
Exogenous vs. Endogenous Cannabinoids
Endogenous cannabinoids, also called endocannabinoids, are neurotransmitters produced within the body that interact with cannabinoid receptors in the central and peripheral nervous system. 
Endocannabinoids include anandamide (a fatty acid neurotransmitter) and 2-arachidonoyl glycerol (a compound formed from the omega-6 fatty acid arachidonic acid and glycerol).
Cannabis compounds, such as CBD, can also bind to and activate cannabinoid receptors in the body. These are called exogenous cannabinoids because they originate outside the body. 
Exogenous cannabinoids include synthetic compounds as well as natural compounds present in cannabis and other plants, which can also affect cannabinoid receptors.
Cannabinoid Receptors (CBRs)
Cannabinoid receptors (CBRs) are present in the central nervous system (brain and spinal cord) and peripheral nervous system.
The two primary types of receptors found in the ECS are the CB1 and CB2 receptors (referred to as G-protein-coupled receptors), although additional receptors may be a part of this system. 
CB1 receptors are present in the central and peripheral nervous system, whereas CB2 receptors are primarily located in peripheral tissues of the immune system. 
CBD exerts therapeutic effects on the body by activating the ECS. Endocannabinoids bind to these receptors and signal the ECS to perform specific actions. 
For example, when an endocannabinoid binds to a CB1 receptor, it can stimulate a pain-relieving effect, whereas when an endocannabinoid binds to a CB2 receptor, it can activate the immune system.
Mechanism of Action
CBD exhibits anti-inflammatory, antioxidant, anticonvulsant, analgesic, and immunomodulatory effects in the body. The mechanisms by which CBD influences these reactions are not yet fully understood.
All cannabinoids, including CBD, function as ligands, meaning they can attach to the binding site of a cannabinoid receptor and influence its behaviour.  CBD works within the body by influencing CBRs and mimicking the effects of endocannabinoids.
However, CBD can also exert effects independent of ECS receptors. For example, CBD can influence the levels of various neurotransmitters, including adenosine, serotonin, noradrenaline, dopamine, and GABA in the body to produce physiological effects. 
CBD also appears to prevent the breakdown of the body’s natural endocannabinoids.
Research on CBD in Other Species
Studies in humans and animals are currently exploring CBD’s effectiveness in treating a wide range of conditions.
This research is often relied upon to suggest therapeutic benefits in horses. However, evidence of effects in other species does not necessarily mean the same effects will be observed in horses.
Even if CBD binds to the same receptors in each species, the duration of binding to the receptor and affinity for it may differ, thus altering the effects experienced in the animal. 
Inflammation and Pain
Studies in multiple animal species, including cats, dogs, and mice, show that CBD possesses anti-inflammatory effects. 
CBD is being studied for its beneficial effects on relieving inflammation and pain associated with joint disease, neuropathic disorders, skin issues, gastrointestinal illness, and other conditions. 
Topical CBD application to the knee joint of rats demonstrated therapeutic potential for relief of arthritis pain-related behaviours, swelling, pain, and inflammation. No side effects were reported. 
Brain Function and Behaviour Modification
CBD may have positive effects on reducing psychotic, anxiety, and depressive behaviours. This is attributed to CBD’s effects on altering the central nervous system. 
Research in humans and animals shows that CBD can also help to reduce brain damage associated with neurodegenerative conditions and those involving impaired blood supply (ischemic conditions, e.g. stroke). 
Findings from animal models and human trials have confirmed the anticonvulsant effect of CBD.  However, further research is needed to establish effective dosages and determine efficacy in different species. 
CBD for Human Use
Applications for CBD use in humans that are currently being investigated include: 
- Seizure related disorders
- Depression and anxiety
- Cardiovascular disease
- Neurodegenerative disease
Effects of CBD in Horses
Research on the benefits of CBD in horses is limited. Most of the available research on CBD has focused on humans and animals such as mice, rats, and pigs.
Some of the recent research on CBD use in horses is summarized as follows:
Case Report on Pain Relief
A case report documented the use of CBD in a 4-year-old mare with extreme sensitivity when touched near the shoulder region. The mare was diagnosed with mechanical allodynia (pain from a light stroke or brush).
Oral administration of CBD two times per day eliminated the pain rapidly. CBD was given to the mare after several other treatment strategies had failed. 
The effectiveness of CBD for reducing inflammation in horses is currently being investigated.
- A study investigating the effectiveness of a 99.9% CBD powder as an anti-inflammatory agent determined a 4 µg/mL dose of CBD reduced the production of inflammatory signalling protein molecules (cytokines) when blood was collected from senior horses and tested under artificial conditions (in vitro). 
- An in vitro study found that CBD influences COX-1, COX-2 and LOX enzymes that modulate inflammation. 
- A study that investigated the effects of CBD on immune function in 13 horses over 90 days found that it reduced the production of certain inflammatory markers with no negative side effects. 
CBD Metabolism in Horses
CBD is metabolized in the liver and intestines.  Research studies are currently investigating the time it takes for CBD and its by-products (metabolites) to clear from the blood, tissues, and organs of horses.
Although mammals produce similar metabolites following the metabolization of CBD, the rate of metabolization differs between species.
A study investigating the pharmacokinetics and bioavailability of cannabidiol in senior horses determined that CBD was undetectable in plasma 24 hours following administration at an oral dose of 2 mg/kg or intravenous dose of 0.1 mg/kg.
However, the 7-COOH CBD metabolite was still detectible in senior horses at 264 hours after a single dose. 
Safety & Tolerance
The Tolerable Upper Intake Level (UL) of CBD for horses has not yet been established. The UL refers to the highest average daily amount that is safe for horses to consume.
Most studies have investigated CBD use in horses at doses between 0.5 and 2mg/kg of body weight. For a 500 kg (1100 lb) horse, this is between 250 – 1000 mg per day.
Research studies have determined CBD is safe at the following administered doses and durations:
- Senior horses had no adverse effects from a single oral or intravenous dose of 2 mg/kg of body weight of CBD. 
- CBD at a dosage of 0.35 mg/kg or 2.0 mg/kg once daily for seven days was well-tolerated by mature horses. 
- CBD-containing feed that provided 150mg was readily consumed and did not result in changes in mentation, gait, or other health parameters. No adverse clinical signs were observed during 56 days of oral administration of the CBD product. 
- Exercising thoroughbreds that received a single oral dose (0.5, 1, and 2 mg/kg) of CBD suspended in oil showed this amount was well tolerated, with no significant behavioural, gastrointestinal, or cardiac abnormalities observed. 
Types of CBD Products for Horses
Aside from humans, companion animals and horses are the second largest target market for CBD products.
In Canada, CBD products that do not make any health claims may be sold lawfully under the Cannabis Act. There are currently no Health Canada-approved CBD medications for animals.
In the USA, CBD is regulated by the Federal Drug Administration (FDA). There are currently no FDA-approved CBD products for animal use.
In the USA and Canada, CBD products are available in a range of formats, including:
CBD Oils: CBD oils are usually the most potent and unprocessed form of cannabidiol. These oils have been removed directly from the flowers, stalks, and seeds of the hemp plant.
CBD Tinctures: Tinctures contain CBD but are typically less potent than CBD oil. The CBD in a tincture has been extracted with alcohol or another solvent.
Edible CBD Products: Pellets and treats are formulated with CBD in them.
Topicals: Creams, lotions, salves, gels, rollers, and sprays containing CBD are commonly used for joint comfort and muscle tension.
Various formulations are being researched (i.e. oral, intravenous, topical etc.) to determine which CBD preparations and delivery methods are most effective in horses.
CBD-containing products are typically recommended to be administered according to the animal’s body weight. Follow the dosage directions provided by the manufacturer of the CBD product you are using.
Typical daily dosages of CBD for horses range from 0.5 to 1.5 mg per kg of body weight. There is no standardized dosage or concentration of CBD products for horses.
When using a CBD tincture, the product should indicate how much CBD is contained within the entire bottle. Concentrations vary and dosages must be adjusted according to the potency of the formulation.
Safety & Toxicity
Research suggests CBD is safe for both animals and humans when administered at recommended dosages. 
CBD may interact with other medications and should be administered cautiously and according to the product manufacturer’s directions. 
If your horse is being treated for a medical condition or has been prescribed medication, consult with your veterinarian to determine if this product is safe for your horse.
Considerations for Using CBD
- Veterinarians cannot legally recommend, administer, or prescribe CBD in Canada or the US. However, owners can legally administer CBD to their own horses. 
- Consult with a veterinarian before administering CBD to your horse to determine overall health status. Some equine health symptoms may indicate an underlying disease that requires treatment.
- CBD is not a miracle cure for any ailments or diseases, but may provide some therapeutic benefits.
- Strictly follow the manufacturer’s instructions regarding dosage before administering any CBD product to your horse to avoid adverse effects.
- Purchase CBD from a reputable company. CBD manufacturers and distributors should be able to provide proof of current good manufacturing processes (CGMP) and a COA (certificate of analysis) from a third-party testing laboratory for their products.
- CBD is prohibited by the Fédération Equestre Internationale (FEI) for use in competition horses and is a banned substance. 
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