For cancer or any other critical illness you need (1) find a reputable dispensary or cannabis maker (2) what I mean by reputable is the product needs to be accompanied by lab results which clearly outines the % of CBD, % THC, % CBDA,% THCA, a% of other terpenes of the plant AS WELL AS the potency (anything below 60% is not worth it) (3) For Cancer you need the whole plant extract (google entourage effect) not just one isolated cannabidiol molecule whehter it is CBD or THC, it MUST be the whole plant. For instance, my dog and I use a high CBD oil which is 20:1 (meaning 20 parts CBD to 1 THC). For cancer, the best ratio out there is 1:1 meaning 1 part CBD and 1 part THC.
If you live in a state where you can get a medical card, please do so. Also search for cannabis doctors that can best guide you with dosing and ratios. I can give you two names of two that work out of California but they can do phone consults worldwide (note: by law they cannot sell you cannabis or give a medical card but they can sure guide you where to get them) one is Dr. Allan Frankel out of Santa Monica Los Angeles CA and the other one is Calla Spring Wellness out of San Francisco both are experts in dealing with cancer diagnosis. Just for your own education google Zelda Theraupeutics Pancreatic Cancer Clinical Trial so you can read how cannabis researchers have paired up with oncologist in clinical trials abroad (Australia) and recently they have made progress in the area of breast, brain, and pancreatic cancer.
I hope this helps.