Can you report someone for smoking crystal meth?

I just found out somebody who was once close to me has been smoking crystal meth.

I live in the UK and I'm not sure what the laws are on it's usage but I want to report this to the police, however I'm not sure if it's illegal to be caught with it in your system.

Can somebody please advise me? I'm at a loss.

: http://alcoholdrugstreatment.info/can-you-report-someone-for-smoking-crystal-meth