This is my theory about what happened (please note, this is ALL pure speculation!):
SSR may have smoked marijuana before, but Rhea and Showik gave him *something* (maybe laced pot or some other drug) on the Europe trip that triggered some sort of reaction.
This reaction may not have happened on purpose, but realizing that they can get control of his money, they isolate him from his friends and family and continue feeding him both illegal and prescription drugs to keep him "under control."
Eventually, SSR starts to "wake up" and wants control of his life back.
Disha dies mysteriously, causing SSR to become even more erratic and unpredictable from the controller's perspective.
The controller(s) gets nervous/angry/afraid that SSR may know too much and they don't want him talking.
"Suicide" happens.