The majority of medications, CBD included, are broken down by CYP450, the family of liver enzymes. CBD blocks some enzymes in this family. Certain drugs break down at a slower pace now, and side-effects could increase. The drugs are more potent. Your doctor has to lower the dose of these meds. On other drugs, CBD induces some of the enzymes so that the breakdown of the drugs is speeded up. Now the drugs are less effective, and the dose has to be increased.