Cannabis is widely used by people living with cancer. Studies have found it relieves cancer- and chemotherapy-related symptoms such as pain, nausea and appetite loss. Celebrities like Olivia Newton-John and Tom Brokaw have been public about using it to manage their cancer pain.

But now a new study published in the journal BMJ is refuting the claims that marijuana has a profound effect on cancer pain, CNN reports.

Researchers analyzed six randomized control trials of nearly 1,500 people living with cancer in the United Kingdom and Europe. Studies compared the pain levels of individuals on opioid treatment when they added marijuana to further help with pain management to those of people given a placebo.

The study found no difference in average pain intensity between people who used weed and people who took a placebo. The study authors concluded that cannabis does not have a role in cancer-related pain and shouldn’t be recommended for pain management.

Several cannabis users also experienced side effects such as dizziness, nausea, vomiting, fatigue and sleepiness. Sometimes these side effects were so severe that some participants dropped out of the study.

Scientists said their review was “rigorously conducted” and included grey literature (high-quality research that is unpublished or has been published in noncommercial form, such as government and research reports). In addition, when only an abstract had been published, study authors were contacted to get more data and information from the full study. Researchers explained that these factors put the study at low risk of bias, thus bolstering their conclusion.

According to J. Leonard Lichtenfeld, MD, MACP, deputy chief medical officer for the American Cancer Society, the studies reviewed are especially credible because the marijuana used was from countries where its quality is highly regulated, unlike in the United States. (It’s also much more difficult to study cannabis in the United States because it’s still on the list of federally controlled substances.)

“If you go to a shop that sells cannabis in the U.S., you have no guarantee, no warranty, that what you use today will be exactly the same as what you might use a week or two from now,” he said. “There’s no standardization of the product.”

This study provides “good evidence that cannabis is a not a game changer,” Lichtenfeld says. “It’s not a magic drug that is suddenly going to change the face of cancer pain for many cancer patients.” The study did not investigate the use of cannabis for other cancer-related side effects, such as nausea and vomiting.

For related coverage, read “People With Different Diseases Use Medical Marijuana Differently” and “More Oncologists Are Discussing Medical Marijuana With Their Patients.”