Coincidentally, I just interviewed the owners of a medical marijuana dispensary for a newspaper article a couple of weeks ago, so let me interject a few facts here, specifically related to Montana and its laws.
First, to directly address the OP’s question, it depends. The stuff you buy on the street can be just about anything. Which street stuff are you comparing it to? And as for the medical marijuana, the people I interviewed operate a tiny dispensary in a tiny town, and it offers 20+ varieties of differing potency, plus tinctures, oils, teas, capsules, prepared foods (e.g., pasta sauces and cookies with pre-measured dosages), sprays, and even synthetic THC. Bigger dispensaries may offer hundreds of different medical marijuana varieties, blends, and derivative products – all with different potencies.
It certainly is one of the medical benefits, specifically tied to painkilling ability. However, feeling buzzed is neither required nor necessarily desired when using it to combat nausea in chemotherapy patients. And some studies hint that it actually stops progression of certain types of arthritis–again, without needing to “get high.”