Not before. Before is always bad. That maxim was proved true when a substitute teacher passed out from heroin use. In the middle of his classroom.
According to police, Christopher Chiappetta was subbing for an art class at Northgate in Pittsburgh when he took a ten-minute break around noon. He came back to his class and promptly passed out. Chiappetta initially denied it was from drug use.
Police say it wasn’t until they found four baggies of heroin in Chiapetta’s pocket and marijuana in his car that the substitute confessed to using heroin,
So again, do what ever you'd like, but do it in the comfort of your own home. And definitely not when you are shaping young minds