Benicar (olmesartan) onset. Benicar (olmesartan) (B) is a member of the angiotensin receptor blocker (ARB) class of drugs. It works by remodeling the endothelium (E) of blood vessels, which makes them less stiff and it lowers BP that way. It takes about 2 weeks for B to remodel the E. Once B is stopped, the E begins to change to become stiffer, or less compliant and the BP rises. So, the answer to your question is about 2 weeks.