Actually, your wrong.
Liquor is in mummy and daddys cabinet, Heroin isnt.
Similarly, mummy and daddy (or mummy and daddy of friends) can buy it for them legally.
Older friends can also go and buy it for younger ones, and older boyfriend can go and buy it for younger girlfriend and girlfriends friends.
I will say though some drugs might be more cost effective for teens.
Depends what kind of mummy and daddy you have.
Maybe I was exaggerating to say it's easier to get your hands on them but it's certainly easier for high school teens to buy illegal drugs. Obviously there's always a way to get your hands on anything.