I don't know if there are many official studies but there are many reports in people using it with great results. I personally used thc oil and for me it was great for pain relief and helped with all the chemo side effects. I'm now 3 years clear from cancer so I personally would highly recommend it alongside regular treatment.

I used high dose thc oil throughout my treatment for stage 4 bowel cancer and although I can't say it helped reduce the cancer but it sure helped make treatment a lot more bearable.