Are you saying that no Baha'i's suffer with mental health issues? The reality is that we have doctors for a reason. The Bible writer, Luke was a physician, just as @adrian009 is. Would he put aside his medical training to treat a fellow Baha'i presenting with mental health issues, to engage in some kind of faith healing? Would he hesitate to prescribe what is considered the appropriate medication for a serious mental health issue?
If Cannabis becomes a legal medicine, able to successfully treat many different physical and mental conditions, would there be any reason to avoid it?
Baha'is are prone to the same physical and psychological illnesses that everyone else is. The Baha'i writings emphasise seeking advice from compotent physicians.
There is a growing body of literature that supports application of spiritual principles to daily life can have benificial health outcomes both mentally and physically. Harold Koenig wrote an excellent paper reviewing medical literature on this and is a leading advocate worldwide.
https://www.hindawi.com/journals/isrn/2012/278730/
There is strong evidence the cannabis can have a detrimental affect on both psychological and physical well being.