Numerous studies suggest clearly that long-term marijuana use reduces IQ.
Perhaps in the future we'll have customized DNA-derived profiles that accurately tell whether someone is better doing no weed, lots of weed, some weed, and so on and so forth for all chemicals. We all have unique chemical makeups, after all.
Some background: My father was an extensively published pharmaceutical (toxicology, pharmacology, brain expert) academic researcher. Drugs are entirely about dosage. The logic applies here.
FBI policy may be antiquated but does exist for a good reason. Perhaps that reason needs refinement at a societal level, through technological progress.
I do expect this comment to get downvoted. HN'ed.