Even though medical marijuana might be legal in your state and you may hold a medical marijuana card, you still need to practice proper workplace etiquette when taking your medicine.
Make sure to take the given dosage and not go overboard. Showing up to work out of your mind only furthers negative feelings around the legalization of marijuana and gives it a bad name. Trying to keep work separate from your marijuana usage is not always possible if you have a disorder that requires it, but try to remember to respect those around you.
Ask your boss and co-workers their opinion and make sure everyone is on the same page, especially if you do have your medical marjuana card.