If it is from a doctor and based on medical need, then there is no problem as long as you don't promote it among others and it is locally legal. Really no different, from addictive drugs like morphine and opiods.
Virtually anything that can make you "high" other than alcohol is not allowed unless prescribed by a doctor for a medial need.
Of course doing anything publicly that could "stumble" someone (like walking down the street smoking a joint) would earn you a quick trip to the back room after the next meeting.
Rub a Dub