A compound of the marijuana plant may prevent aggressive breast cancers from spreading throughout the body, new research from the United States suggests.

A team of researchers at the California Pacific Medical Center Research Institute say cannabis compound CBD could provide a non-toxic alternative to chemotherapy for cancer treatments. Previous research has shown the compound can block human brain cancers, and recent lab experiments have shown it may be able to do the same for breast cancer.

"Right now we have a limited range of options in treating aggressive forms of cancer. Those treatments, such as chemotherapy, can be effective but they can also be extremely toxic and difficult for patients," said researcher Dr. Sean McAllister in a release. "This compound offers the hope of a non-toxic therapy that could achieve the same results without any of the painful side effects."

CBD works by blocking the activity of gene Id-1, which is associated with metastasis— the spread of cancer cells away from the original tumour site. The compound does not share marijuana's psychoactive properties.

"We know that Id-1 is a key regulator of the spread of breast cancer," said senior author Dr. Pierre-Yves Desprez in a release. "We also know that Id-1 has also been found at higher levels in other forms of cancer. So what is exciting about this study is that if CBD can inhibit Id-1 in breast cancer cells, then it may also prove effective at stopping the spread of cancer cells in other forms of the disease, such as colon and brain or prostate cancer."

Researchers stressed that they were not encouraging cancer patients to smoke pot, adding that it would be highly unlikely for patients to receive an effective concentration of the compound in that way.

The team's findings were published in the journal Molecular Cancer Therapeutics.