Marijuana and hemp indeed both come from the cannabis family. The difference between the two is their chemical makeup, particularly their levels of psychoactive THC. Hemp does not contain a level of THC higher than 0.3%, while marijuana can have a THC level of up to 30%. The very low percentage of THC in hemp will be nearly impossible to get high off of, while the 30% level of THC in marijuana will definitely make you high.
However, switching to CBD oil from a conventional medication is far from a random stab in the dark. In fact, there was a large scale (and very well-documented) survey carried out less than two years ago that looked at precisely what percentage of patients were able to “swap” their side effect-inducing meds for a 100% natural, cannabis-based therapy.