they're so set in their ways!!
this is a direct result from their televisons programming them.
living through the "just say no" era must of damaged their brains.

i try to get my parents to toke up all the time. to no avail.
once, i DID get my mom to say she'd smoke a bowl with me tho!!
see, shes always pressuring me to go to this chiropractor. im like..umm..my back/neck is fine
after months of this, i was like..ok..ill go to your silly doctor if you smoke a bowl of weed with me.
she said ok!!!

unfortunately i never got any weed since then
but it worked.
so
try to see if you can blackmail them into it.
Oxys kill. Pot will heal.