Although not routinely reported, exposure to cannabis can lead to allergic reactions in certain individuals. An increased observation of cannabis allergic reactions is just one more unanticipated consequence of marijuana legalization and subsequent widespread cultivation across the country. Marijuana, like other plant allergens with peanuts topping the list, can cause a range of allergic reactions from a runny nose, itchy eyes, skin rash to labored breathing and anaphylactic shock. The unique and multiple modes of exposure to cannabis sets it apart from other allergens. The following allergies have been reported to be associated with Cannabis sativa: allergic rhinitis (Stokes et al. 2000), allergic conjunctivitis (Mayoral et al. 2008), asthma (Kumar & Gupta 2013), food allergy (Stadtmauer et al. 2003), eczema (Herzinger et al. 2011), contact urticarial or hives (Ozyurt et al. 2014) and anaphylaxis (Tessmer et al. 2012).
The most common means to diagnose a specific allergic reaction is through a skin prick test, where the surface of the skin on the back or forearm is scratched and the allergen is applied. Another testing method is by a simple blood test to measure the levels of specific immunoglobulin E (IgE) molecules, one of the 5 classes of proteins in the serum and cells of the immune system, that function as antibodies and interact with specific proteins found in the plant. Elevated concentrations of IgE are generally thought of in the context of allergic disease. However, increases in the amount of circulating IgE can also be found in various other diseases, including primary immunodeficiencies, infections, inflammatory diseases, and malignancies. Rarely is the skin prick test or an IgE blood test carried out for suspected cannabis allergy suffers, particularly in those states where marijuana is still considered illegal as currently there are no commercial allergen reagents or blood test on the market for cannabis.
It may be just as well that a cannabis allergy cannot be properly diagnosed because there is no recourse through the normal allergen desensitization process of exposing patients to the allergen to lessen their reactions; ie. there are no commercial cannabis extracts available as allergens for desensitization treatment. And for those patients with an established diagnosis of allergic disease to cannabis, measurement of total IgE is necessary for identification of candidates for omalizumab (anti-IgE) therapy, and for determination of proper dosing. What is clearly still unknown is what are the cannabis constituents that are capable of illiciting the allergic response? A few culprits have been proposed and they range from delta-9-tetrahydrocannabinol (THC) (Herzinger et al. 2011) itself to a nonspecific lipid transfer protein (Larramendi et al. 2013).
Conversely, cannabis sensitization has been reported. Across 545 patients reporting atopy, a form of allergy in which a hypersensitivity reaction such as dermatitis or asthma occurs in a part of the body not in contact with the allergen, 8.1% presented a positive skin prick skin test to cannabis leaf extracts. A closer look at the group showed that amongst casual marijuana users, the positive reaction increased to 14.5% and amongst regular marijuana users, it jumped to 18.2% compared with 5% for nonsmokers (Larramendi et al. 2013).
For the burgeoning cannabis industry, occupational exposure to C. sativa presents a unique serum allergen-specific IgE-mediated response. Some individuals will develop contact urticarial (hives) from chronic exposure just through handling of the plant. And it is not known whether or not the process of concentrating the cannabinoids eliminates the allergic potential inherent in the plant. As with other allergens, avoidance is recommended
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