2. July 2020
Cannabis can trigger allergies

It is a little known fact that cannabis can also trigger allergic reactions. The allergy can occur after smoking it but also after eating foods containing cannabis.

Leaves of the cannabis sativa plant. Hemp is one of the oldest useful plants – and intoxicants – in the world

At the European allergy congress EAACI 2020, a Swiss research team presented the cases of two young women to illustrate the different ways a cannabis allergy can occur.


  • The first woman developed a rash (urticaria) after smoking a joint. She had symptoms not just from smoking but also whenever her skin came into contact with female cannabis sativa plants. This would trigger rhinoconjuctivitis, an inflammation of the nasal mucosa and conjunctiva of the eyes. The symptoms are a runny nose and itchy, swollen eyes.
  • The second woman experienced a rash (urticaria), light-headedness, abdominal cramps and diarrhoea after drinking an almond milkshake containing cannabis. These symptoms indicated a third degree anaphylactic reaction, which is a dangerous health situation. In this case, the allergy was caused by the exposure of the gastrointestinal tract to cannabis.

The woman was allergic to birch pollen and already had asthma.


Study director Zita-Rose Majali Thomas of University Hospital of Basel believes that cannabis allergies may be under-diagnosed.

Sensitisation can occur through smoking, skin contact and ingestion. But the allergic reaction can occur in different ways. Foods containing cannabis can also trigger a cross reaction.


What the research team investigated

The protein Can s3 is responsible for cannabis allergy. The Swiss researchers were only able to confirm the cannabis allergy after several tests.


  • Prick test: For this test, different allergens are applied to the skin. Both women had positive reactions, which appeared to indicate an allergy.
  • The first woman was also administered a scratch test. For this test, the surface of the skin is scratched open and the allergen is rubbed into the small wounds. The test result was clearly positive in her case.
  • IgE test: This test checks for antibodies to cannabis in the blood. Both women tested negative, which did not indicate an allergy. It also means that antibody testing alone with the IgE blood test is not always sufficient for a diagnosis.
  • Basophil activation test (BAT): The BAT is done in a test tube in which the suspected allergen is added to the blood. In the presence of an allergy, basophilic granulocytes are activated, which belong to the white blood cells and are involved in immediate hypersensitivity reactions (type I). The BAT is an additional diagnostic test that is used when the IgE test produces negative results despite a strong suspicion of an allergy. The test confirmed the allergy in both women.




Majali Thomas ZR et al. Allergy to Cannabis sativa – two illustrative cases of an old drug with new relevance. EAACI 2020 poster session