Originally posted by: Atomic Playboy
Based on evidence taken from my own group of friends, no, that's absolutely not true.
Friend A: Has used virtually every drug under the sun; tobacco, caffeine, alcohol, marijuana, cocaine, heroin, meth, PCP, LSD, mushrooms, salvia and lots and lots of different prescription drugs (both narcotic and non-narcotic). Currently in the military, was completely sober during his stint in Iraq last year, came back and began drinking and doing dip again, but off the harder drugs as they test for those.
Friend B: A long and troubling history with drugs, he spent several months living on the street selling marijuana and crystal meth. He used crystal habitually, saying that he would go weeks without sleeping. Currently has been completely free of methamphetamines for 4 years, though he still drinks alcohol and smokes marijuana regularly, as well as occasionally using cocaine. Often seems to be addicted to marijuana, spending much of his time either smoking or looking for pot.
Friend C: Similar to friend A, experimented with everything he could get his hands on from a young age, became addicted to heroin in his late teen years. Currently he is sober from heroin for 3 years after attending rehab. Still drinks and smokes, occasionally uses cocaine.
So simply based on what I've seen of drugs, I think it's preposterous to say "once a junkie, always a junkie." However, I do see that people who were addicted to drugs will continue using substances, even if it's not as hard as whatever they were addicted to.