I'm very curious by what standard "Just Say No" could be deemed a success? If it was the lowering in price and the heightening in potency, then it was a great success!
The worst consequence of JSN was that it treated all drugs equally. Marijuana was just as bad as heroin which was just as bad as crack. When the children of JSN grew up, went to college, smoked weed and didn't see their lives instantly destroyed, they knew they had been lied to. And if marijuana isn't that bad, maybe heroin isn't that bad either? And heroin would make a resurgence in the early 90s with devastating consequences.
By lying to kids about the dangers of drugs it taught them not to trust the government. That’s about the only success I can think of.