Answered by: Maulana Tahsin Alam
If I didn’t know that weed has an effect on my salah, is my salah going to be accepted?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
The validity of salah does not revolve around one’s knowledge of the effects of marijuana but rather on the effects of its consumption on the body.
If the drugs were such that one loses complete control of their body and are oblivious to their surroundings, then such a person’s wudu would have been deemed to be broken and their salah is in need of repetition. If a person did not reach such a state, his wudu will be thought to be intact and his salah valid.
Such a person’s salah will be valid but will not receive the full reward of their salah as they are committing a sin whilst performing their prayer. One should make Tauba and Istighfaar for these actions.
Only Allah knows best
Written by Maulana Tahsin Alam
Checked and approved Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Imam Nasafi, Kanzud Daqaaiq (Karachi: MaktabahBushra, 2012) volume 1, pg. 18. (with reference to Bahr Raaiq).