Is it Possible to be Allergic to Weed?

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Cannabis sativa belongs to the family of hemp. It is natively found in Central Asia and is cultivated in moderately temperate climates. Its leaves are used to make weed, which is also popularly known as marijuana, pot, hashish or hashish oil. This substance contains high levels of cannabinoids, which usually produces euphoric effects with adequate exposure. Because of its psychoactive effects, weed is often used as a recreational drug that is considered illegal in most countries. Extracts from its dried leaves and flowers are usually crushed. These are made into cigarettes or are placed into pipes. These are commonly smoked or vaporized. Some users incorporated this in their food and beverages for consumption. Because this plant contains proteins, it can cause allergic reactions to susceptible individuals.

Prevalence of Cannabis Allergy

The precise global prevalence of cannabis allergy is unknown. Although, there has been numerous published case reports of allergic reactions to marijuana exposure. The first documented case report of cannabis allergy occurred in 1971, wherein a 29 year-old female was diagnosed with cannabis allergy after smoking a marijuana cigarette. Scratch testing and passive transfer studies were positive confirming the diagnosis. The incidence of cannabis allergy may be underreported in literature due to the lack of a routine diagnostic test to support the diagnosis. It can also be attributable to the reluctance of patients to consult because it is a prohibited substance.

Routes of Exposure and Sensitization

Allergy to cannabis may be obtained through several routes. Since this substance is popularly rolled into cigarettes, smoking, vaporizing and smoke inhalation of its allergic contents may sensitize susceptible individuals. In some case reports, skin contact with leaves or parts of the plant elicits an evanescent red rash characteristic of an allergic reaction. Since Cannabis sativa plant produces pollens, inhalation of pollen by allergic individuals can trigger hypersensitivity leading to an allergic attack. Pollen in itself may contain an allergen that can produce an allergic reaction.

Cannabis Allergens

Generally, allergens are proteins that trigger an allergic reaction by binding to specific antibodies. These allergy mediators are called IgE. Once IgE binding occurs, a cascade of immunologic cellular events occurs. This often produces various clinical manifestations that prompts a person to seek medical attention. The exact protein composition of the cannabis allergen remains to be established. However, there are published researches that investigated possible protein allergens. One protein is called the “oxygen-evolving enhancer protein 2”, which is an enzyme necessary for photosynthetic reactions. Another protein is the heavy-chain subunit of the enzyme, ribulose-1,5-biphosphate carboxylase/oxygenase, which is also important for photosynthesis. These proteins were found to bind to IgE in experimental investigations. Other studies identified other proteins that equally bind to IgE. These proteins are profilin, Can s 3 and thaumatin-like protein.

Clinical Manifestations

Like any allergy, symptoms may vary from mild to life-threatening manifestations. In published case reports, those who are exposed with cannabis through the respiratory route by smoking or vaporizing produce symptoms within the respiratory tree. Patients describe runny nose, wheezing, persistent coughing, and in worst cases, difficulty of breathing. Some patients also describe having itchiness and excessive tearing to smoke exposure. There have been reports of allergic individuals presenting with skin erythema, itchiness, skin warmth and blistering. Usually, these are individuals who had dermal contact with the plant and its parts. Airborne exposure to cannabis pollen may trigger swelling around the eyes and respiratory symptoms. Life-threatening presentation of anaphylactic shock may occur to susceptible individuals who have systemically absorbed the allergens through food consumption.


This is a phenomenon whereby there is cross-reactivity between the allergens of cannabis and plant-derived food. This condition is known as “cannabis-fruit/vegetable syndrome”. Patients with allergy to cannabis could also develop allergies to certain fruits and vegetables like banana, peaches, tomato, grapefruit, orange and apple. Usually, the presentation of this syndrome is more severe than the usual food allergy.


Clinicians usually perform a detailed history taking to be able to determine the substance causing an allergy. Inaccuracies in history due to patient reluctance to admit prohibited substance use often leads to a delay in diagnosis. A simple test that can be done to establish the diagnosis is the prick-prick testing. This utilizes mashed Cannabis leaves and flowers that are introduced through the skin’s dermal layer. A positive result will yield erythema. Although this test lacks standardization, it is useful in determining an allergy to Cannabis. Another method is through quantification of blood levels of IgE antibodies after exposure to industrial hemp. This is commercially produced but its utility needs to be clinically investigated. Lastly, a component resolved diagnosis can be made, wherein a distinct biomarker is used to study a patient’s allergic profile towards specific allergens. Since this test utilizes specific allergens, it can also diagnose cross-sensitization with plant-derived allergens. However, these tests are not yet standard and are usually utilized in the research setting.


Currently, there are no treatment guidelines that exist for cannabis allergy or cannabis-fruit/vegetable syndrome. Patients are usually given anti-histamines and supportive therapy. Once the diagnosis of cannabis allergy is established, patients are counseled to avoid exposure to the cannabis plant, and the fruits and vegetables that are implicated in cross-sensitization. Since these substances are usually prohibited, patients are also referred for addiction counseling.

Author: Marinelle C

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References :

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