Allergic reactions to cannabis and its many forms were not oft-reported in medical literature until recently. This trend has changed over the last decade, however. Cases of rashes, hypersensitivity, and even anaphylaxis due to contact with cannabis pollen, plants, or smoke are on the rise.

The rise in incidences of reported allergic reactions may in part be due to the increasing acceptance of cannabis use medicinally and recreationally around the country.

As more states legislate the accepted uses of cannabis, the stigma surrounding its use has lessened and more folks may be coming forward seeking treatment for allergic reactions than had previously in the past.

There may, however, be some corroboration with THC levels. As THC levels continue to rise, so does the probability of allergic reactions to cannabis.

Cannabis as an Allergen

Allergies to all or parts of the leaves, flowers, seeds, and pollen of plants is common the world over. Cannabis is, after all, a plant and as such there is bound to be a percentage of the population that experiences an allergic reaction when exposed to it.

Inhalation of cannabis, either through its pollen or smoke can cause numerous afflictions. This effect can be exacerbated in late summer or early fall for residents that dwell near either its native habitat or near outdoor plantations when the plant naturally sheds its buoyant pollen—it can travel for many miles on a current of wind.

Inhalation of cannabis pollen has been reported to cause nasal irritation, sinusitis, pharyngitis, rhinitis (inflammation in the nose causing stuffy or runny noses or post-nasal drip), and sneezing, according to the study “Cannabis sativa: the unconventional ‘weed’ allergen.”

In many areas of the world where cannabis is native to the area, allergies to it are seemingly as common as ragweed allergies in the United States and Canada. A recent study published in the Pakistan Journal of Botany looked at residents of Islamabad, Pakistan and found that cannabis pollen was the most abundant of allergens found in the city during the fall.

A previous Pakistani study found that up to 45 per cent of the residents suffered from allergic reactions to cannabis including asthma and rhinitis. This is not unique to this part of the world. In the US Midwest, Nebraska residents are exposed to cannabis pollen levels comprising as much as 36 per cent of the airborne pollen in late summer to early fall.

This area of the US now grows significant quantities of hemp. Studies in Spain and Italy report similar pollen counts when cannabis there blooms in August.

In one unusual Canadian case, an individual showed severe allergic reactions to the ingestion of hemp seeds, but no reaction to frequent consumption of recreational marijuana. Allergic reactions to hemp seeds, like cannabis in general, is not commonly found in medical journals.

The individual in question drank a smoothie containing hemp seeds and almost immediately developed lip and facial swelling, abdominal pain, and difficulty breathing, such that epinephrine was required to restore normal breathing. That same patient self-admitted as a regular smoker of cannabis.

Individuals that physically handle the plant, even if they do not use it themselves, have been reported to have had topical allergic reactions. Cases of Urticaria (hives), Pruritis (itching anywhere on the body due to exposure of an allergen), and Periorbital angioedema (swelling around the eyes) have been reported.

As the legitimate cannabis industry continues to grow and employ individuals to grow and harvest it, it is important that employers keep these in mind and ensure that appropriate protective equipment is in place for their employees.

These same symptoms have been found to also occur in individuals that do not smoke cannabis, but chew or otherwise ingest it by ways other than smoking.

Cross-reactivity

Numerous studies, mostly European, have found definitive cases where cannabis use has caused allergic reactions in numerous food and fiber substances. This phenomenon has been dubbed “cannabis-fruit/vegetable syndrome” (as if we needed another excuse not to eat our fruits and veggies) or alternatively, “cannabis-plant syndrome”.

Foods most commonly implicated with this syndrome include: peaches, cherries, bananas, apples, nuts, and some citrus fruits. Allergic reactions to wheat, tobacco, wine, beer, or other foods with hops as an ingredient and latex have all been reported as well.

Unfortunately, there is not yet any cure for sufferers of this syndrome. Even the cessation of cannabis use does not reverse the food allergies that have developed; once it occurs, it seems to be there for good.

Even worse, there is some evidence that the cross-reactions leading to food allergies can be caused by passive and indirect contact with cannabis, such that even if an individual that has never actively consumed cannabis and only encountered it unknowingly, such as through pollen inhalation or second-hand smoke, could develop these reactions.