[JimRed]

99.999% of all pot smokers never go on to heroin.

Source, please?

Or how about rewording it "99.999% of all pot smokers never go on to other drugs and see if it fits?

[Mariner]

There are 669,000 people in the US who used heroin in the last year:

https://www.drugabuse.gov/publications/research-reports/heroin/scope-heroin-use-in-united-states

That’s .2%

52% of Americans have tried pot:

http://www.nbcnews.com/news/us-news/new-poll-finds-majority-americans-have-smoked-pot-n747476

That’s over 150,000,000.

Looks like it’s only 99.5% who try pot do not go on to become heroin addicts.