It might be Marijuana which is an extremely popular deppresent drug in the U.S. currently.
Marijuana has also become legal in many states so that could lead to it being more widely used since there is no fear of repercussions among users. Furthermore, marijuana is also used as a medicinal drug which further broadens its reach.
As for being widely used, marijuana is popular among teens and young adults so it would not be unusual if that resulted in wild usage.