How to Tell If You’re Allergic to Weed

Having a marijuana allergy isn't overly common, but as the cannabis plant is legalized in more and more states, symptoms of allergic reactions are also on the rise. As with other allergens, reactions to the marijuana plant occur when the immune system believes the substance is an invader and tries to fight it off. 

While antihistamines can often be used to counteract the initial symptoms after encountering cannabis allergens (pollen, plant material, infused products), the best long-term solution is usually to limit your exposure to the plant.

Signs You're Allergic to Weed

Marijuana allergy symptoms resemble symptoms of allergies to other substances like pollen, hay fever, and contact dermatitis. Others in the home could also experience allergy symptoms from second-hand cannabis smoke, like this 6-year-old boy in Seattle, WA.

After inhaling cannabis pollen or smoking marijuana, someone with an allergy might experience:

• Congestion

• A runny nose

• Sneezing

• Coughing

• Itchy, red, or watering eyes

• An itchy or sore throat

Within an hour or so after applying cannabis-infused topicals, someone who is allergic to marijuana might experience symptoms of dermatitis, including:

• Dry skin

• Red and inflamed skin

• Itchiness

• Hives

• Blisters

Ingesting cannabis-infused edibles or parts of marijuana plants (such as in smoothies or juice) could cause:

• Swelling of the skin

• A rash or hives

• Red or swollen eyes

• Difficulty speaking

• Shortness of breath

While it's not common, there have been reports of people experiencing an anaphylactic reaction to hemp seeds. Symptoms of anaphylaxis include:

• Swelling of the tongue or throat

• Difficulty breathing

• Itchy skin that may be pale or flushed

• A sudden drop in blood pressure

• A weak, racing pulse

• Dizziness

• Fainting

• Vomiting

As anaphylaxis can be life-threatening, people with a severe marijuana allergy may need to carry an epinephrine injector (such as an EpiPen) with them at all times. If you experience a severe allergic reaction to marijuana involving the symptoms listed above, seek emergency medical attention immediately.

Who Is Most at Risk of a Marijuana Allergy?

Anyone can develop a weed allergy—even after consuming high-quality cannabis concentrates for years without any problems. However, a small study published in 2018 indicates that people could be at greater risk of a cannabis allergy if they are allergic to plants, molds, dust mites, or cat dander.

You're also more likely to have or develop a marijuana allergy if you are allergic to foods that have similar protein properties to cannabis, including:

• Tree nuts, including almonds and chestnuts

• Stone fruits, including apples and peaches

• Tomato

• Grapefruit

• Eggplant

• Banana

How Are Marijuana Allergies Diagnosed?

If you suspect you might be allergic to marijuana, a doctor can perform a skin prick test or blood test to confirm the allergy.

What Happens in a Skin Prick Test

In a skin prick test, a small amount of the allergen is placed directly on a small prick or scrape in the skin. If you have an allergic sensitization to the substance, the area will typically swell and itch.

What Happens in a Blood Test

Blood tests look for a higher-than-usual number of antibodies to a substance as an indicator that you are allergic. Blood tests involve fewer skin pricks than skin tests, but the results take longer to process.

Marijuana Allergy Treatment

The most obvious treatment for a marijuana allergy is to stop consuming, touching, and breathing in cannabis. If you regularly consume medical marijuana, ask your supervising doctor about alternative treatments for your symptoms or ways to make your allergy symptoms less severe.

In the case of a severe allergy or anaphylaxis, you may need to carry an epinephrine auto-injector at all times. Mild allergic reactions can generally be managed with allergy medications such as antihistamines, but you would still need to cease consumption.

Other Kinds of Reactions to Cannabis

Cannabis products can cause other reactions even if you're not allergic to marijuana. Two of the most common are side effects from specific cannabinoids and cannabinoid hyperemesis syndrome (CHS). 

Uncomfortable Side Effects from Specific Cannabinoids

Some cannabis consumers who react to the proteins in the cannabis plant are fine with cannabinoid isolates and distillates (as the plant proteins have been removed). However, it's still possible for cannabinoids to cause side effects, especially if consumed in large amounts. 

CBD, for example, can cause drowsiness, lightheadedness, low blood pressure, and dry mouth. THC (especially in excess) can cause dry mouth, paranoia, headaches, nausea and vomiting, and a racing heart. A good rule of thumb is to stick with the lowest effective dose and go easy on new products and strains.

Cannabinoid Hyperemesis Syndrome

Though it’s still extremely rare, CHS is becoming more common here in Seattle and across the U.S. Cannabinoid hyperemesis syndrome is the name given to severe and ongoing nausea and vomiting after consuming cannabis. Heavy, long-term consumers are most at risk of developing CHS (most cannabis consumers are fine). The only solution for CHS is to cease consumption. 

If you do start to experience nausea after smoking or ingesting cannabis, take a shower for instant relief and take a break from marijuana for a few weeks. You might be able to continue consuming cannabis occasionally without any ill effects.

Tips for Minimizing Allergic Reactions

Whether or not you’ve already experienced allergy symptoms, these safety tips can help:

• Try a small amount of any new cannabis-infused topical on the inside of your elbow (which tends to be more sensitive) and wait for a few hours to see if you react before applying the product more broadly.

• Try only a small amount of any new smokable, inhalable, or edible cannabis product the first time to see how it affects you.

• Go low and slow with new cannabis products and strains and take care not to go over your limit. 

• Make sure you know what good weed likes like and how to tell if weed is moldy. Inhaling mold spores can make you sick.

• If you experience allergic symptoms up to an hour or more after exposure to cannabis, stop touching, inhaling, smoking, or ingesting the plant and move away.

• If you are allergic to marijuana and can't avoid exposure entirely, wear a dust mask or respirator and gloves.

Most People Don't Need to Worry

The good news is that—while it does occur—marijuana allergy isn't all that common and if you're not allergic to things like dust mites, cat dander, or mold, it's less likely that you're allergic to marijuana. 

However, if you're starting to experience allergy symptoms like a runny nose or itchy skin after exposure to cannabis, take a break and follow up with your doctor for testing. Once you know exactly what's bothering you, you’ll be able to make informed decisions from there.