Medicinal uses for cannabis: Epilepsy

Epilepsy is a neurological condition which affects approximately 1 in 100 people. Depending on how wide spread in the brain the neuroligical disturbance is (the focus), there are a range of possible seizures from lapses in consciousness (absence) or convulsions (Grand Mal) to grimacing or repetitive movements (temporal) to just odd sensations (auras). Epilepsy is as individual as the people who have it and everyone has their own patterns of seizures. There are sometimes triggers for seizures such as sleep loss, low blood sugar, stress or even boredom. Some common causes of epilpsy include head trauma, birth injury, hormonal imbalances, and viral attacks.

Some kinds of epilepsy can be well controlled by anti-convulsant drugs, but a few forms do not react well to these. Anti-convulsant drugs have potentially serious side-effects, including bone softening, reduced production of red blood cells, swelling of the gums, and emotional disturbances. Other occasional effects include uncontrollable rapid eye movements, loss of motor co-ordination, coma and even death. In addition, these medications are far from ideal in that they only completely stop seizures in about 60% of patients.

Cannabis has long been known to have anti-convulsant properties, and these have been investigated from the 19th century. Large amounts of anecdotal reports and 1-patient case studies indicate the assistance of cannabis in controlling seizures. Cannabis analogues have been shown to prevent seizures when given in combination with prescription drugs. Patients report that they can wean themselves off prescription drugs, and still not experience seizures if they have a regular supply of cannabis.

Some interest has been shown in the use of cannabidiol (a cannabinoid) in treatment. A small amount of data is available about this, and cannabidiol has little or none of the psychoactive side-effects that treatment with cannabis (or THC) could induce. There seems to be no plans to make a great effort to concentrate on cannabis research in the field of epilepsy at present. The British Medical Association has however stated that it may possibly prove useful as an 'adjunctive therapy' for patients who cannot be kept satisfactorily free of seizures on current medications. Likewise, the National Institutes of Health workshop considered that this is 'an area of potential value', based largely on animal research showing anticonvulsant effects.

Scientific evidence

Unfortunately there has been relatively little research done into the treatment of epilepsy with cannabis-based medication. Most evidence comes from anecdotal reports and studies on individual cases.

In 1949 Davis & Ramsey administered THC to 5 institutionalized children who were not responding to the standard treatment (phenobarbital and phenoytin). One became entirely free of seizures, one almost completely free of seizures, while the other three did no worse than before.

In 1975 Consroe et al. described the case of young man whose standard treatment (phenobarbital and phenytoin), didn't control his seizures. When he began to smoke cannabis socially he had no seizures. However when he took only cannabis the seizures returned. They concluded that 'marihuana may possess an anti-convulsant effect in human epilepsy'.

Three controlled trials have investigated the anti-epilepsy potential of cannabidiol. In each, cannabidiol was given in oral form to sufferers of generalised grand mail or focal seizures.

Cunha et al (1980) reported a study on 16 grand mal patients who were not doing well on conventional medication. They recieved their regular medication and either 200-300mg cannabidiol or a placebo. Of the patients who received the cannabis product, 3 showed complete improvement, 2 partial, 2 minor, while 1 remained unchanged. The only unwanted effect was mild sedation. Of the patients who received the placebo, 1 improved and 7 remained unchanged.

Ames (1986) reported a less successful study in which 12 epileptic patients were given 200-300mg of cannabidiol per day, in addition to standard antiepileptic drugs. There seemed to be no significant improvement in seizure frequency. This is a finding that was replicated in a report by Trembly et al (1990). However, Trembly performed an open trial with a single patient who was given 900-1200mg of cannabidiol a day for 10 months. This trial showed a more positive result - seizure frequency was markedly reduced in the patient.

It must be stated that these trials are all over too small a population for any general statements about efficacy to be made.

A study by Ng (1990) involved a larger population of 308 epileptic patients who had been admitted to hospital after their first seizure. They were compared to a control population of 294 patients who had not had seizures, and it was found that using cannabis seemed to reduce the likelihood of having a seizure. However this study was criticised in an Institute of Medicine report (1999) which claimed it was 'weak', as 'the study did not include measures of health status prior to hospital admissions...and differences in their health status might have influenced their drug use' rather than the other way round.

Finally, there is some weak anatomical evidence of a relationship between cannabinoids and epilepsy. There is a dense concentration of CB1-type receptors in the hippocampus and amygdala areas of the brain. These two regions of the brain are known to be involved somehow in seizures.


Ames FR. (1986) Anticonvulsant effect of cannabidiol. South African Medical Journal 69:14.

Consroe, P.F., Wood, G.C. & Buchsbaum, H. (1975) Anticonvulsant Nature of Marihuana Smoking. J.American Medical Association 234 306-307

Cunha, J.M., Carlini, E.A., Pereira, A.E. et al. (1980) Chronic Administration of Cannabidiol to Healthy Volunteers and Epileptic Patients. Pharmacology 21 175-185

Davis, J P., & Ramsey, H.H. (1949) Antiepileptic Action of Marijuana-active Substances. Federation Proceedings 8 284-285

Institute of Medicine (1999) Marijuana and medicine: Assessing the science base. National Academy Press

National Institutes of Health (1997) Workshop on the Medical Utility of Marijuana, Report to the Director, Washington, D.C.

Ng et al. (1990) Illicit drug use and the risk of new-onset seizures, American Journal of Epidemiology 132: 47-57.

Trembly B. Sherman M. (1990) Double-blind clinical study of cannabidiol as a secondary anticonvulsant. Marijuana '90 International Conference on Cannabis and Cannabinoids. Kolympari, Crete, July 8-11, 1990.

Other information

This comment is from Eleanor Logan, Chair of the Youth Commission of the International Bureau for Epilepsy, and a former fundraiser for Enlighten, Action for Epilepsy in Edinburgh:

'Each anti-convulsant drug has its own suite of side effects and people with epilepsy have to decide whether these are counterbalanced by seizure control. Not everyone experiences the side effects, and it can take up to 2 years to find the right drug and more importantly the right level of medication to give control.
In the last 10 years there has been a great increase in the variety of drugs available to treat epilepsy as well as the development of surgery. In addition, there has been a great increase in research into alternative methods of treating epilepsy, including a self control method and aromatherapy. I don't know anything about treatment of epilepsy with cannabis.' is a large site with lots of general information about epilepsy. Some sections are still under construction at present.