A new study found that nearly half of U.S. breast cancer patients were using cannabis products while receiving treatment and warned that it could be dangerous.

In a survey by the American Cancer Society, 612 breast cancer patients were asked whether or not they used marijuana while receiving treatment. Forty-two percent of respondents, or 257 people, reported that they were and only 23% said that they were using it for medical purposes.

Few of the participants said that they spoke about this with their doctor. As for reasons why they did not, 28% disclosed that they were uncomfortable sharing details of their drug use with their medical provider.

This omission, however, can be dangerous as researchers warn in the study.

Doctors note that cannabis use can have medical benefits, particularly for treating instances of chronic pain or anxiety. Seventy-eight percent of survey participants said that they used it to treat pain while another 57% were to treat anxiety.

However, another 49% said that they were using cannabis to treat the cancer itself. This has never been proven and federal regulators have previously warned against products that are advertising marijuana as a cancer cure.

Where this becomes dangerous is when patients choose to self-treat with marijuana without knowing how it can impact their treatment for breast cancer. Half of the survey participants who reported using marijuana said that they sought out medical information on how it would affect their health, but only 4% said this came from a physician. The most common source was a family member or friend at 22%.

Pot users in the survey were found to commonly believe that the benefits of the products outweighed any risks that may be attached.

Many were convinced that pot use was completely safe without acknowledging that safety varied based on their source. Most said they acquired cannabis from a medical dispensary, but 33% said it came from a friend or family member and 6% said it was from a drug dealer. The study says state-regulated sites were the safest, but warned that differences in legality and price pushes people toward less-safe options.

Eighteen states allow recreational marijuana use and another 36 allow it for medical purposes. Under federal law, marijuana is still considered an illegal substance.

There is also the potential risk that using marijuana while undergoing treatment like chemotherapy can put more strain on the body. Cannabis products are processed by the same parts of the liver as chemotherapy drugs which can risk overworking the organ.

The researchers also note that breast radiation treatments were found to carry a higher risk of lung and mortality risk for tobacco smokers than non-smokers. Tobacco is a common component of many marijuana products, but the authors note that there is no conclusive link between smoking cannabis and any impact on cancer treatments.

This also speaks to the fact that research on cannabis smoking or the use of other cannabis products remains vague. The study touches on how previous research was conducted on in vitro, or controlled, settings and the clinical implications of these remain unclear.

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