The laws pertaining to marijuana (hashish) have been treated by Imam al-Zarkashi in his treatise Zahr al-’Arish fi Tahrim al-Hashish. In this work (p.9) he states that the consumption of this substance for medical reasons would be permissible if proven that it does indeed help. From here it would be extrapolated that growing the plant would be permissible, but strictly and exclusively for medical purposes. Where the least bit of ambivalence exists around the intention for growing it, either at present or potentially in future, its cultivation should rather be left to others to whom the laws of Islam do not apply.

And Allah Knows Best

Answered by Shaykh Taha Karaan