Also known as The Impure and Head, Premonition (1972) is a cautionary horror turd about the ramifications of doing non-prescription drugs.
College hippies, not content with chugging Nyquil™ or snorting crushed up baby aspirin to open their doors of perception, find red flowers with reputed mind-expanding properties, and decide to put that to the test. But a rose by any other name is not exactly so in this case.
Once the flower’s fun stuff gets into your body, you experience premonitions about your own death. (Note: this does not happen when you try to get high off yellow or lavender flowers. Those will just make you load yer britches.)
And if you didn’t figure it out, each dies in the manner they premonitioned. I tried the red flower and “saw” myself drowning in beer. The flower was right — I’ve been doing that every day of my life.