How is it hard to harass someone on drug charges, if they are not using or possessing drugs at the time of a police stop?
"Can I search your vehicle / bag?"
"Affording my constitutional rights, No."
Now the police either has to show a judge probable cause to get a warrant, or they let you go. So called "reasonable suspicion" doesn't even work because there has to be some form of evidence for that - if you don't have dilated pupils, slurred speech, or loss of coordination / balance they don't have that either.
Know your rights, and exercise them, and most cops don't get to play their cop games. If they do it anyway, you've got a nice legal settlement coming from the city / county / state.