There are marked differences in the knowledge on the medical uses of cannabis and cannabinoids in different diseases. For nausea and vomiting associated with cancer chemotherapy, anorexia and cachexia in HIV/AIDS, spasticity in multiple sclerosis and spinal cord injury there is strong evidence for medical benefits. For many other indications, such as epilepsy, movement disorders and depression there is much less available data.
Clinical studies with single cannabinoids or, less often with whole plant preparations (smoked marijuana, encapsulated cannabis extract) have often been inspired by positive anecdotal experiences of patients employing crude cannabis products. The anti-emetic, the appetite enhancing, relaxing effects, analgesia, and therapeutic use in Tourette's syndrome were all discovered in this manner.
Incidental observations have also revealed therapeutically useful effects in a study with patients with Alzheimer's disease wherein the primary issue was an examination of the appetite- stimulating effects of THC. Not only appetite and body weight increased, but disturbed behaviour among the patients also decreased. The discovery of decreased intraocular pressure with THC administration in the beginning of the 1970s was also serendipitous. For this reason, more surveys have been conducted in the past decade questioning individuals that use cannabis therapeutically.
(Press agency article):
An Ontario judge ruled on Wednesday that a Toronto man could grow and use marijuana to control his severe epilepsy, saying the law banning the medicinal use of the drug was unconstitutional. The landmark ruling was a major victory for advocates of the legalization of marijuana for medical use and for defendant Terrence Parker, 42, who has fought for 20 years to use the drug to control his severe form of epilepsy. (…)
The Epilepsy Association of Toronto welcomed the ruling, saying: "We feel people should have opportunities and options to choose from. People who have epilepsy, by in large, are on medication to try and control their seizures. Lots of them do not get control of their seizures through those medicines and are searching for another way."
Source: Reuters of 10 December 1997.
(Gordan and Devinsky):
Animal and human research on the effects of marijuana on seizure activity are inconclusive. There are currently insufficient data to determine whether occasional or chronic marijuana use influences seizure frequency. Some evidence suggests that marijuana and its active cannabinoids have antiepileptic effects, but these may be specific to partial or tonic-clonic seizures. In some animal models, marijuana or its constituents can lower the seizure threshold and thus facilitate seizures. Preliminary, uncontrolled clinical studies suggest that cannabidiol may have antiepileptic effects in humans. (...) Marijuana use or withdrawal could potentially trigger seizures in susceptible patients.
Modified according to: Gordon E, Devinsky O. Alcohol and marijuana: effects on epilepsy and use by patients with epilepsy. Epilepsia 2001 Oct;42(10):1266-72.
(Carlini and Cunha):
Fifteen patients suffering from secondary generalized epilepsy refractory to known antiepileptic drugs received either 200 to 300 mg cannabidiol daily or placebo for as long as 4.5 months. Seven out of the eight epileptics receiving cannabidiol had improvement of their disease state, whereas only one placebo patient improved.
Source: Carlini EA, Cunha JM. Hypnotic and antiepileptic effects of cannabidiol. J Clin Pharmacol 1981;21(8-9 Suppl):417S-427S.
(U.S. Institute of Medicine):
There are anecdotal and individual case reports that marijuana controls seizures in epileptics, but there is no solid evidence to support this belief. While there are no studies indicating that either marijuana or THC worsen seizures, there is no scientific basis to justify such studies. (...)
The potential anti-epileptic activity of cannabidiol (CBD) has been investigated, but is not promising. Three controlled trials were conducted in which cannabidiol was given orally to patients with generalized grand mal seizures or focal seizures. Two of these studies were never published. (...)
Even if CBD had anti-epileptic properties, these studies were likely too small to demonstrate efficacy. Proving efficacy of anticonvulstants generally requires large numbers of patients followed for months because the frequency of seizures are highly variable and the response to therapy varies depending on seizure type.
Source: Joy JE, Watson SJ, Benson JA, eds. Marijuana and Medicine: Assessing the Science Base. Washington DC: Institute of Medicine, National Academy Press, 1999.
If possible, slowly increasing doses should be applied in a titrated fashion to avoid undesirable side effects on psyche and circulation. Starting doses are 2 x 2.5 mg or 2 x 5.0 mg of dronabinol per day. Dosages may be increased up to several units of 10 mg daily. In appetite loss and nausea due to AIDS 5-20 mg THC daily are usually sufficient, pain treatment may often need higher doses. If natural cannabis products of unknown THC content are used orally, the patient should begin with about 0.05-0.1 grams of the drug (for cannabis with an average THC content of 5 percent this corresponds to 2.5-5 mg THC). If the THc content is unknown, a store of cannabis sufficient for several weeks should be layed in so that a constant quality is ensured. In a study by Fairbairn and colleagues (1976) the THC content of marijuana only decreased by 7% within 47 weeks with dark, dry storage at 5°C, and by 13% at a temperature of 20°C.
To achieve reproducible effects cannabis or THC should be ingested always under similar conditions with regard to food intake, e.g. always one hour before a meal. If natural cannabis preparations are used doses should be weighed carefully and taken with the same carrier, e.g. cannabis tea with half a gram of dried cannabis flowers on half a liter of water and some cream.
As with opiates, some side effects may decrease within some days or weeks, thereby increasing the acceptance of the drug. Prolonged THC ingestion causes tolerance to unwanted effects on circulation and to psychological effects, so that daily doses of more than 50 mg THC may sometimes be taken without significant unwanted psychic or physical side effects. Heavy regular users in western societies may smoke five to ten cannabis cigarettes per day or more, thus well tolerating daily doses of 100 mg THC and more. In a sample of cannabis users analyzed by Solowij (1991) mean weekly consumption was 766 mg THC, ranging from 30-2400 mg THC.
Tolerance may also arise with respect to therapeutically desired effects (e.g. decrease of intraocular pressure, pain reduction), and require increased doses after some time of treatment.
Modified according to: Grotenhermen F. Harm reduction associated with inhalation and oral administration of cannabis and THC. Journal of Cannabis Therapeutics 2001;1(3-4):133-152.