That's what his electronic thingamabob was for...
Yeah, I never figured out the point of that gizmo. Apparently it's all right to achieve an altered mental state from an electronic device, but not by puffing some plant in a pipe.
Klingons are allowed to commit ritual suicide and murder if it's crouched in religious hokum.
Yes he's allowed actual drugs, if it's forced on him by his religious beliefs.
But Chakotay appears to be a wussy taking the wussy way out.