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What Are Mycotoxins and How Do They Affect Weed?

cannabis flower

Mycotoxins are poisonous compounds produced by certain species of fungi, such as powdery mildew, aspergillus, and penicillin. These compounds can be found on some living cannabis plants and processed cannabis products and, if ingested, can cause severe health issues.

To ensure consumer safety, many states require that cannabis products are tested for the presence of mycotoxins before they’re allowed to be sold.

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What Are Mycotoxins?

Mycotoxins are small molecules made by certain fungi (or molds — mold is a type of fungi) that harm the human body when consumed. Most mycotoxins are secondary metabolites used to protect the fungi against viruses, help fungi heal from damage, and protect fungi against UV light.

Mycotoxin-producing fungi are found on a wide range of crops. Some common plants susceptible to mycotoxin-producing fungi are corn, wheat, cannabis, and even fruits like apples and strawberries.

The existing threat from mycotoxin contamination of agricultural products means that there are already well-established testing methods for mycotoxins.

How Do They Develop?

Mycotoxins are produced when fungal spores contact plant material such as cannabis flowers, leaves, or roots and find suitable conditions for growth. These conditions include sufficient water, as fungi and molds thrive in damp, humid conditions. As soon as the fungi or mold starts growing, it will begin to produce mycotoxins.

Cannabis, its extracts, edibles, and other cannabis preparations are all vulnerable to contamination from fungal spores. Contamination can occur from the soil, contact with other infected plants or products, contaminated tools, and even the air, which can contain fungal spores.

While anyone handling cannabis should take care to prevent contamination from mycotoxin-producing fungi, it is extremely difficult to eliminate the possibility of the plant or product coming in contact with mycotoxin-producing fungal spores. Therefore, regular testing and removal of any possible places the mold can grow can be just as, if not more, important.


Once contamination has occurred, and the conditions are right for fungi and mold to grow, they start to infect the host plant, causing damage and slowing the plant’s growth. Specific areas such as leaves, roots, or buds may be affected, or the entire plant can be infected. Any plant tissue near mold growth can contain mycotoxins, resulting in a poisonous product.

Some cannabis strains require high humidity levels, providing a damp environment where mold can grow. If the plants don’t have enough space or airflow, moisture can collect on the leaves and buds, allowing the growth of fungi.

Commercial growers need to carefully monitor humidity levels, allowing enough moisture for the plants to thrive but not so much that it would encourage the growth of mold and fungi. Proper trimming of leaves and sufficient ventilation are essential to prevent mold and fungi from thriving.  Overwatering can also create conditions perfect for mold, as waterlogged soil and coconut fibers contained within the growing medium are common sources of mycotoxin-producing fungi.


After harvest, growers and producers still need to monitor humidity levels carefully. If the flower buds are not dried correctly, enough moisture can remain in the center of the bud to allow mold to grow. Although part of the quality of cannabis products comes from a slow curing process, if the process takes too long, mold may grow before the bud is fully dried. This mold may or may not be visible outside the bud.

Growers and producers still need to be careful about potential contamination with fungal spores. If an infected bud goes through processing machinery, it will contaminate any product that follows.

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The Dangers of Mycotoxins

Many medical marijuana patients may have compromised immune systems or other health problems that may make them particularly sensitive to mycotoxins. In addition, some mycotoxins, such as ochratoxin A, can accumulate in the body over time, making long-term exposure a significant concern. Most testing focuses on two types of mycotoxins: aflatoxins and ochratoxin A.


While over twenty aflatoxins have been identified, the most dangerous ones are aflatoxins B1, B2, G1, and G2. These are produced by the Aspergillus family of molds, some of which can cause the life-threatening disease aspergillosis when inhaled.

Symptoms of aflatoxin poisoning include nausea, vomiting, convulsions, liver damage, and liver cancer. Aflatoxin B1 is the most toxic of the four main aflatoxins, but all are known to be highly carcinogenic and harmful to human health.

Ochratoxin A

Ochratoxin A is produced by aspergillus and by members of the penicillin species. Ochratoxin A is one of the more common mycotoxins found in food and can cause damage to the kidneys. It also suppresses the immune system, allowing other infections to thrive. Symptoms of Ochratoxin A poisoning include fatigue, diarrhea, and tremors.

Regulations and Testing


In the United States, cannabis buds are not considered part of the food industry and are not covered by the FDA. Therefore, the states set the maximum allowed level of any toxins in cannabis buds, if any. Most states have testing regulations that cover potential contaminants such as heavy metals, pesticide residues, and fungal species.

Regulatory limits for cannabis mycotoxin testing can vary significantly between states. Most agree that mycotoxin testing is essential, and the maximum allowable limit is 20 μg of mycotoxin per kilo of product. However, the exact details vary considerably.

In Illinois, for example, cannabis testing requirements state that there may be no more than 20 μg of any of the five mycotoxins mentioned above per kilo of product. This allows a kilo sample to contain almost 100 μg of mycotoxins: 20 μg each of aflatoxins B1, B2, G1, and G2, and 20 μg of ochratoxin A. This is four times more aflatoxins than the standards the FDA sets for human food, which is 20 μg per kilo of aflatoxins.

In Nevada and California, the regulations match those that the FDA has set for food, with no more than 20 μg per kilo of aflatoxins and 20 μg of ochratoxin present per kilo of product. New Mexico has the strictest regulations, with the maximum allowed levels not exceeding 20 μg total of mycotoxins, including aflatoxins and ochratoxin A.

Although these are good starting benchmarks, more research still needs to be done on the health risks of inhaling mycotoxins in cannabis smoke. Current regulations are based on the safe levels of mycotoxins in food and not in inhaled smoke. Over time, these regulations are likely to change as new data comes to light.


A certified laboratory must complete the final testing of cannabis products. However, growers can test for the presence of mycotoxins themselves using testing strips.

Testing strips work using the antibody-antigen relationship. There are two types of testing strips: qualitative and quantitative strips. In both cases, the cannabis sample (either the bud or the leaf) is combined with an extraction solvent. A testing strip covered in antibodies is then exposed to the mixture. If the antibodies on the strip come in contact with mycotoxins, the testing strip will change color.

Qualitative strips check the quality of the sample. The testing strip will change color once a certain amount of mycotoxins are detected. Very low levels of mycotoxin won’t be picked up with the testing strip, and you won’t be able to determine how much mycotoxin contamination is present if you get a positive result. However, for home growers and users, these are an easy way to check your cannabis for potential contamination.

Quantitative strips check the quantity of mycotoxins. These are slightly more tricky to use and often require an electronic test strip reader. However, they are accurate and can detect mycotoxin levels down to two micrograms per kilo — one-tenth of the average regulatory limit. Quantitative strips are helpful in the cannabis industry as they are accurate and require little training.

To pass most local regulations, cannabis products will require a complete mycotoxin analysis from a professional laboratory before selling them. In the laboratory, the standard testing method for mycotoxins uses immunoaffinity column chromatography (ICC), which allows detailed analysis of the quantity and type of mycotoxins present.

The plant’s extracted juice is added to a small tube containing beads covered in mycotoxin-binding antibodies in ICC. When an antibody comes into contact with a mycotoxin, it attaches to it firmly. This stops the mycotoxins from being washed through the beads but lets everything else through.

A special solvent is then used to remove the mycotoxin from the antibody-covered beads. The mycotoxin can then be measured with fine precision using fluorometry, in which fluorescent dye binds to the mycotoxins. The brighter the dye, the more mycotoxins are present. ICC is an incredibly sensitive detection method through which mycotoxins can be detected down to 0.5 micrograms per kilo of product.

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The Bottom Line

Mycotoxins can be present in any cannabis product infected with, or that has been in contact with, mycotoxin-producing molds and fungi. Mycotoxins can be extremely harmful when ingested, so states often require producers to conduct testing to ensure that mycotoxins aren’t present in dangerous amounts.

Producers need to maintain careful humidity levels to prevent mold growth and check for mycotoxins’ presence using testing strips. If you suspect your cannabis buds have been in contact with mold, you should throw them away.

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Frequently Asked Questions

Do all molds release mycotoxins?

No, not all molds release mycotoxins. Some fungi produce large amounts of mycotoxins, while others produce none.

Is cannabis mold toxic?

Some cannabis molds aren’t toxic, but enough are to warrant extreme caution. If you see any mold on your cannabis, it (and the surrounding bud) are unsuitable for use. Smoking buds with Aspergillus spores can be life-threatening, so it’s best not to take the risk. Cannabis mold will also often affect the flavor of the smoke or edible. If you taste or smell something "off" about your cannabis, it’s best not to use it.

Can you trim out bud rot?

When considering an entire plant, if only one bud is infected with bud rot, that stem can be removed, and the rest of the plant may still be suitable for use. In regards to one specific bud, it is not safe to remove the moldy areas and use the rest of the bud. Mycotoxins spread throughout the bud and are invisible, so you can’t safely remove moldy patches.