Being in a club when it's raided...

[Lettish]

My friend would like some info on the below scenario, if it would happen.

He heard a rumour that his usual nightclub has recently been under investigation, and that there are a few undercover cops placed there. He also heard that it had been raided a few times. My friend informs me that this club is a drug farm and most people are off their face.

My friend says to prevent complications and not get busted, he will never carry anything on him, just in case he is searched. But say, for argument's sake, he had dropped a few pills and was rolling, and then the club was raided, what could the cops do? If they found nothing on him but suspected he had consumed drugs, could they take him away and test him?

My friend apologises if this is the wrong forum, he thinks it is E-related.