If I strongly suspect someone of using drugs should I warn others around them?

[Susanne]

i am in case like yours, the neighbors got something going on. it is always new lady next door or guy. sudafed is not against the law.
it cough medicine.

rule in life, don't gossip about people. they might be come after you
later on. it is like someone is drinking, maybe they are drinking.
not using drugs.

you need new friends, you do not write anything on facebook, or anywhere, they can sue for character defamation. it might be hard to
get money out of you. i would not do it.

instead ask to go to church with you.