Adults only (18+)

Does THC Help Seizures?

Cannabis has long been discussed in the context of epilepsy and seizure disorders, particularly for people whose symptoms are difficult to control with conventional medication. While much attention has focused on CBD, some are now asking whether THC—the psychoactive compound in cannabis—can help reduce seizures too.

This article is for people living with epilepsy, carers, healthcare professionals and anyone exploring cannabis-based treatment options for seizures. We explain what THC is, what the current research says, and how UK guidance supports or restricts its medical use.

What Is THC and How Does It Work?

THC, or tetrahydrocannabinol, is the main psychoactive compound in cannabis. It interacts with CB1 and CB2 receptors in the endocannabinoid system, which plays a role in regulating brain activity, inflammation, pain and immune response.

Because seizures are caused by abnormal electrical activity in the brain, researchers have investigated whether cannabinoids such as THC might help stabilise these signals and reduce seizure frequency or severity.

What Does the Evidence Say?

The scientific evidence on THC for seizures is limited and mixed. Most high-quality studies on cannabis and epilepsy focus on CBD (cannabidiol) rather than THC. This is because CBD does not cause intoxication and has shown clearer benefit in clinical trials for certain types of epilepsy, such as Dravet syndrome and Lennox-Gastaut syndrome.

THC, on the other hand, is more controversial. While some animal studies and anecdotal reports suggest it may have anticonvulsant properties, others have shown that THC might trigger or worsen seizures, particularly at higher doses. The way THC affects seizures may depend on:

The type of epilepsy
The specific dosage
The ratio of THC to CBD
The individual’s unique brain chemistry

Because of this variability, THC is not considered a reliable or safe standalone treatment for seizures in clinical practice.

CBD vs THC: What’s the Difference for Epilepsy?

CBD has a different mechanism of action from THC and is better tolerated. In the UK, Epidyolex, a purified CBD oil, is licensed for treatment-resistant epilepsy in children with Dravet syndrome or Lennox-Gastaut syndrome. It contains no THC and is prescribed by specialist neurologists under strict conditions.

By contrast, THC-containing products like Sativex are licensed only for multiple sclerosis-related spasticity and not for epilepsy. While Sativex includes both THC and CBD, it is not routinely used in seizure management.

Are There Any THC-Based Products Prescribed for Seizures in the UK?

At present, no THC-based medicines are licensed or routinely prescribed in the UK for epilepsy. Medical cannabis products containing THC may occasionally be prescribed off-label by specialist doctors in private clinics, but this is rare and only considered when all other treatments have failed.

The British Paediatric Neurology Association (BPNA) and NHS England remain cautious about prescribing THC for epilepsy due to concerns about side effects, limited evidence and potential harm, especially in children and young adults.

Potential Benefits

Some patients and families report improved seizure control using cannabis oils that contain both THC and CBD. However, these products are often sourced from overseas or unregulated markets, making consistency, safety and legality a concern.

There is a small group of individuals who may respond well to THC as part of a carefully balanced cannabis formulation. However, this requires medical oversight, careful dosing and strict monitoring for adverse effects.

Risks and Side Effects

THC can cause a range of side effects, especially at higher doses. These include:

Drowsiness or fatigue
Confusion or memory issues
Mood changes, anxiety or paranoia
Reduced concentration
Hallucinations in rare cases
Dependence with long-term use

In people with epilepsy, high doses of THC could potentially increase seizure risk, particularly if taken without medical supervision or alongside other medications that interact with the brain.

For this reason, most doctors and epilepsy specialists recommend avoiding recreational cannabis and high-THC products unless prescribed for a specific medical purpose.

Legal Status and Access in the UK

Cannabis containing THC is a Class B controlled drug under the Misuse of Drugs Act 1971. However, since November 2018, specialist consultants in the UK have been allowed to prescribe cannabis-based medicinal products in very limited circumstances.

Prescriptions are typically reserved for cases where:

The condition is severe and treatment-resistant
All licensed medicines have failed
There is reasonable evidence of potential benefit
There is specialist oversight and monitoring

Most cannabis prescriptions in the UK are made privately rather than through the NHS. This is due to tight NHS restrictions and a lack of funding for unlicensed treatments.

Conclusion

THC may have some effects on seizure activity, but the current evidence does not support its routine use for epilepsy. While some individuals may benefit from carefully balanced formulations that include THC, the risks, variability and potential for worsening seizures mean that CBD-only products remain the first-line cannabis-based option for seizure management.

Anyone considering cannabis for epilepsy should speak to a specialist doctor or epilepsy consultant. Recreational cannabis use, particularly with high THC content, is not a safe or recommended method for controlling seizures.