Ideally, you would not take any medications or supplements leading up to the test, however that isn't always possible or recommended, depending on what you take.
I do recommend skipping any non-essential supplements, especially those containing B vitamins (for 3-7 days). If possible, medication doses can be delayed until after the blood draw. Limit or avoid even over the counter medications prior to the draw (Pepto Bismol, Tylenol, Advil, etc). If you have a need for these medications for a recent incident or illness (temporary), it is recommended to wait until you no longer need them for the blood draw. Do not have your blood drawn when you are sick or otherwise not feeling normal.
For any medications that cannot be skipped or delayed, continue taking the normal dosing.