The linguistic link between matters "spiritual" i.e "pharmakeia"" and Sorcery as P.P. points out is no surprise, but what the G.B & Co ignore, or perhaps do not know, is that the Israelites and later the Jews, right down until Roman Occupation times at least, and maybe until 70 C.E ??? burned Cannabis on the Altar at Temples dedicated to the worship of YHWH/Jehovah.
This was done so that the worshippers would have a spiritual experience which they would feel came from the presence of Yahweh.
So can we expect this sometime soon in a G.B, letter ? :
" After careful study, and prayerful consideration of the matter, in the light of Jehovah's evident approval of this practice, the Holy Spirit has guided us to decide that the smoking of cannabis is permitted by you dear brothers, as long as this is done at a time of Worship".