I have a friend who was in rehab for heroin use. They use the 12 step program and although they are not 'Narcotics Anonymous' they did host a Narcotics Anonymous meeting once a week for recovering addicts and family/friends. She's been clean for 3 months now which is the longest she's been clean in years, so fingers crossed. Unfortunately the success rate of AA/NA or any other rehab is not very high (no pun intended), and often repeated attempts and relapses occur before success.
Narcotics Anonymous or NA is NOT the same as Narconon (Note the spelling, narconon, not narcanon) which, as Deenem, pointed out, is based on scientology and is pseudo-scientific and can be dangerous.
(
http://www.na.org.za/ is the legitimate one,
http://www.stopaddiction.co.za/ is the scientology one)
Also, if you're an athiest you may have problems with the 12 steps!