Medical Marijuana Can Reduce Effectiveness of Immunotherapy Cancer Drug, Israeli Research Shows

‘We have known for years that marijuana has a depressive influence on the immune system,’ says one of the study’s researchers

Medical marijuana
Nir Keidar

Cancer patients being treated with medical marijuana and at the same time an immunotherapy drug, which enhances the ability of the immune system to attack the cancer cells in the body, show a greatly reduced response to the drug, a new study suggests.

Researchers at Rambam Medical Center in Haifa presented this conclusion recently at the European Society for Medical Oncology conference in Madrid. Their study is based on the clinical results from 140 patients with lung cancer, melanoma and renal cancer, all of whom took the immunotherapy medicine nivolumab (marketed as Opdivo) in 2015 and 2016. 89 patients received only the drug and 51 other patients received the drug and medical marijuana.

>> Medical marijuana helps kids with cerebral palsy, Israeli study finds <<

The response rate to the treatment with just nivolumab was 37.5 percent, while those who used the drug along with medical marijuana showed a much lower response rate, only 15.9 percent.

The combination of medical marijuana alongside immunotherapy drugs has become relatively widespread in recent years, and thousands of oncology patients in Israel take medical marijuana to mitigate the side effects of the cancer treatments. While the study found the marijuana reduced the response rate to the immunotherapy treatment, the scientists did not find any significant effect on either progression-free survival and overall survival rates for the patients.

An employee sorts freshly harvested cannabis buds at a medical marijuana plantation in northern Israel, March 21, 2017.
NIR ELIAS/REUTERS

“We have known for years that marijuana has a depressive influence on the immune system,” Prof. Gil Barsela, the deputy director of the oncology division at Rambam and one of the authors of the study, along with Dr. Tarek Taha, told Haaretz. This information is supported by research since the 1980s on Aids patients who received medical marijuana together with other drugs, he added.

The scientists differentiated between two groups of patients: Those with non-small-cell lung cancer, an aggressive and fast growing and spreading form of the disease; and those with advanced melanoma or renal clear cell carcinoma – two forms of cancer that are more similar to each than to lung cancer, says Barsela.

One-third of the lung cancer patients treated solely with nivolumab responded to the drug, compared to only 17.6 percent of those treated with the drug and medical marijuana concurrently. Among the melanoma and renal cancer patients, 43.3 percent responded to the drug-only treatment, while only 10 percent of those treated with medical marijuana too responded to the drug.

This was the first study on the effects of medical marijuana on immunotherapy drug treatments, and it has its limitations. First, it is a retrospective study based on already available data, as compared to a planned and controlled study. In addition, it studied a limited number of patients, and those treated with medical marijuana used a number of different strains of the plant, as well as a wide range of dosages and application methods.

The scientists do not deny these limitations and say further research is necessary to examine the influence of the two substances used together. In any case, the results certainly indicate an important direction for further research on the subject. “Considering the limitations of the study, further prospective clinical study is needed to investigate possible interaction,” say the authors, in their paper, “The effect of cannabis use on tumor response to nivolumab in patients with advanced malignancies.”

The research focused on two very high profile treatments at the center of clinical scientific theory today: Immunotherapy, which is considered the promising cutting edge technology in cancer treatment; and medical marijuana, which over 30,000 Israelis use regularly.

“Our research raises the question what the combination of these substances does to the immune system, and could be the basis for developments in deeper basic research on the subject,” says Barsela. “It serves as a good reason to begin to collect precise data systematically, and we have already begun to do so.”