CBD or cannabidiol is one of the compounds found in cannabis. It functions by increasing our bodies own natural cannabinoid levels. Every "body" is different and unique and will respond to different levels of herbal medicines. I would start with a small dose of a few milligrams per day, which should help stimulate the endocannabinoid system. Whole plant, full spectrum extract is also superior (in my humble opinion) to isolated CBD. The entourage effect means that a synergy will occur with the other compounds in cannabis and the effects with be multiplicative instead of additive.