We are lucky here in Colorado. Marijuana is legal both medically and recreationally. Our doctors recommended it and gave my husband the medical marijuana card but we can also supplement as need be with recreational. My husband has a Stage 4 cancer of 'unknown primary' (after 10 months of testing and appointments)....we still don't know the cancer type BUT.......his tumor has gotten smaller and the overall lymph node activity has dropped every 3 months (confirmed via PET Scan) since he started using CBD and THC. Since we are doing no other treatment, we are cautiously optimistic that the marijuana is contributing to the decline in cancer activity. Our doctors are on board. There is an interesting article you can Google from the National Institutes of Health about the effect of CBD and THC for a number of medical concerns......there isn't much research yet because of the legal status but it being used for pain, inflammation and can in some way 'bind' to cancer cells they believe and kill the cells without harming healthy cells.
I am, as of tomorrow, 3 years cancer free from my breast cancer diagnosis and I too have started to use CBD only as a 'preventative'. I have noticed no ill effects. I use a small amount (vaping) before bed and it does relax me somewhat and I sleep well (ha ha). The CBD doesn't create the brain effects of THC but it seems to relax me and reduce some of my old lady pains that might otherwise keep me awake.
My husband has had no negative effects either......marijuana has been used for years and there don't seem to be long term effects for adults that are documented, so I figure........adding it to all the other treatments and options..........why not!!
Hugs.....