Will your doctor know if you smoke marijuana?

It depends on what test(s) your doctor is ordering for you. In many cases, yes, the doctor will know. If you have blood work done, it will show up (as long as this is checked in the blood work). However, in my experience, it seems like many doctors do not really care if you smoke marijuana or not (unless it's a doctor from Social Security for disability or a state appointed doctor for medicaid disability, or if you are seeing this doctor and are attempting to collect worker's comp / short-term disability).