Cannabis is a plant of the family Cannabaecae, originally from central Asia and cultivated in all regions of the world. Cannabis refers to preparations derived from Cannabis sativa indica (Indian hemp); marijuana corresponds to dried flowers of the female plant and contains up to 25% THC (tetrahydrocannabinol, the chemical product responsible for the majority of psychoactive effects) and hashish is a preparation of resin from the plant with a THC content of from 10% to 30%.
Cannabis has been used for recreational purposes for many decades, and for a few years for its medicinal value. An allergy to cannabis has been known for many years, first described in 1971, and is increasing in frequency. Allergic reactions may occur from inhalation, ingestion, skin contact with the cannabis plant or through intravenous injection.
Cannabis in production
A cofactor can increase the severity of the allergic reaction from any allergen (food, medication, insect venom) and there is no reason to think this would be different with cannabis: cofactors include alcohol, the use of NSAIDS, exercise in the hours preceding exposition, and the premenstrual period.
Reactions occur most commonly after direct exposure, but they have also been reported after passive exposure. More than 80% of patients allergic to cannabis have a sensitization to pollens, particularly to birch tree pollen, and to several fruits and vegetables.
Sensitization to cannabis usually occurs after direct contact (smoking, handling, or ingesting cannabis). Passive sensitization (breathing in the smoke of others) has also been described, recently in a 5 year-old child.
A young woman presented for evaluation of an anaphylactic reaction occurring the month prior. Towards 19h00 she began to have difficulty breathing, itching everywhere, with a feeling of choking; all within several minutes: 911 was called, the ambulance arrived and 2 doses of epinephrine were given during transport; arriving at the hospital at 20h00 she felt much better; she had improved after the first dose of epinephrine; she was observed for 6 hours without relapse, and discharged home.
For about 18 months, if she touched cannabis she would have the appearance of hives on her hands for 2 minutes, which disappeared about 1 hour after washing her hands: she smoked it without difficulty and she continued to smoke it without touching it; sometimes her lip would swell if small non-burnt pieces fell into her mouth. Her friend had rolled a joint between his fingers without smoking it, he touched and kissed the patient for several minutes before her anaphylaxis.
A percutaneous skin test with a leaf of cannabis was significantly positive at 15 mm.
The patient described above presented with contact urticaria, an oral allergy syndrome, and lastly, anaphylaxis. She also tested positive to cat, birch tree, ragweed and dust mites, suggesting the eventual development of allergic rhinitis to these additional allergens.
A cannabis allergy is often associated with other allergies through cross-reactions to the principal allergen, LTP (lipid transfer protein) that is found in several vegetables. There are also other allergenic molecules in the cannabis plant.
European authors have coined the term to describe this cross reaction as the "cannabis-fruit and vegetable syndrome", which describes the observation that people allergic to cannabis often subsequently develop an allergy to fruits and vegetables. LTP, which is found in certain fruits, vegetables, legumes, other plants and grains, is responsible for sometimes severe food allergies. This type of allergy is more frequent in southern Europe. This protein of vegetable origin is a powerful allergen. It is resistant to heat and to digestive enzymes, which explains its toxicity. The principal fruits and vegetables associated with this cross reaction are: kiwi, bananas, peaches, apples, cherries, peanuts, certain nuts, potatoes, tomatoes and occasional citrus fruits, certain grains, certain alcoholic drinks (beer and wine) and latex. Additional cross reactions have also been seen with hemp (hemp seed) and tobacco.
It is possible to perform percutaneous prick tests using a part of the plant (flower, stem, leaf or extracts): however these tests have not been standardized and false positive and false negatives are both possible. Tests for specific antibodies (specific IgE) are not yet commercially available. Tests incorporating basophil activation could be useful but are not available commercially. With the legalization of marijuana, it is conceivable that provocation tests or challenges become possible clinically.
Primary prevention, that is to say, avoiding exposure to cannabis, will prevent sensitization.
Once allergic, all forms of exposure should be avoided, and an epinephrine autoinjector should be carried in case of a systemic reaction after accidental exposure. One should also avoid those foods to which one has become allergic through cross reactions.
André Caron, MD FRCPC, allergologue et immunologue
(translation: Andrew Moore, MD FRCPC)
An allergie to cannabis
can present as follows:
- a respiratory allergy
- rhinoconjunctivitis and asthma
- a skin allergy
- contact urticaria, eczema
- a food or GI allergy
- oral allergy, nausea, vomiting, diarrhea
- urticaria and angioedema
Is cannabis safe to use?
Canadian Public Health Association