There is evidence of genetic predispositions to addiction (no single "addiction gene"though) so I believe some people are more inclined to become addicted to things, myself included. Smoking is an example.
But people can kick addiction and never be addicted to anything ever again. It depends on the person. I would never write anyone off as once an addict, always an addict. There are some amazing stories out there of addicts who have turned their lives around through sheer hard work and strength.