Or the longer version of "head." In the late 1960's through the middle 1970's, anyone who was called a "cool head" or just a "head," was an intense party person. (Southern California)They may have only been into one substance (pot) or the entire pharmacy.
Go figure on the name, "head shops" on the west coast. What people would call a "smoke shop" today. They use to be the Disneyland for stoners, but no more.
Because of law enforcement efforts to put these people in jail, code words were used to protect your allies. Nothing has changed.
He's a cool head man, he ain't no #$*&@$% narc!