Is caffeine also at the top of the funnel? How about melatonin? The fact that most heroin users have used caffeine previously does not mean that caffeine is a

Is caffeine also at the top of the funnel? How about melatonin? The fact that most heroin users have used caffeine previously does not mean that caffeine is a gateway drug to heroin, or at all correlated with hard drug use. The same applies to cannabis.