US has imperial for everything but guns and drugs

If we're talking legal drugs, my prescriptions all come in milligrams.

If we're talking illegal drugs, though fractions of ounces or pounds were more common, it wasn't unusual to come across someone selling stuff by the gram back in the day, and I can't imagine that's changed. The weed dude would sell any amount at $10/gram - and yes, I did see someone come with $3 once. 😂 I don't remember the coke dude's prices because that was much longer ago, but he was also totally fine with selling single grams.

Maybe my experience was different because I live in a college town, so the black market was supportive of the small purchases necessitated by student budgets.