He started by pounding whole datura plants between two stones. The difficult part was estimating the quantity and proportion of leaves, stems, and flowers to use.
Don't try this at home.
Seriously. There's a rhyme about the nightshade family alkaloids: Red as a beet, full as a jug, dry as a bone, blind as a bat, hot as hell, mad as a hatter.
Your pulse and blood pressure rise, you retain fluids but can't urinate, your temperature rises but you can't sweat, your vision fades & you experience unpleasant delusions.
Stick to shrooms.