TheUltimateFixx
Bluelighter
Oh yah.Wow, lucky about the heroin. Wish I could get away with it that easy!

Though it took me a good long time to get a habit - about 2 months of daily injecting - and even now I can continue to use twice weekly on average and not experience withdrawal symptoms. (Can't use for much more than 5 days in a row without getting into that territory though ; so as a rule I don't.)
I'm positive there's genetics involved in how quickly you build up a tolerance and how quickly you lose it.