first of in reply to grace you need to add benzodiazepines and barbiturates to alcohol as potentialy life threatening if you suddenly stop.also no 1 has ever died from suddenly stopping heroin.physically withdrawal symptoms are similar to a bad dose of flu which last couple of weeks.Rehabilitation for heroin users might include substituting heroin with methadone,a similar drug but without the euphoria that heroin creates. which is prescribed and allows the user to stabilise his addiction.They will then be slowly weaned of methadone until clean.to keep the heroin user from relapsing implants or tablets called naltrexone are used.these stop heroin or any other opiates from having any effect.psychological treatments will continue before during and after the user has become clean.these will include counselling,therapy,group work and possible medication such as anti depressants.
alcohol is treated slightly different.Because of the risks of seizures and other life threatening problems alcoholics are usualy treated as an in patient in hospital where they are monitored closely.Instead of cutting down alcohol slowly drugs such as diazepam and librium are used instead as they have similar effects on the brain chemistry as alcohol but are easier to taper down and are less dangerous.also diazepam is used to stop seizures.When clean from alcohol implants or tablets called antabuse are used.if alcohol is drunk the drinker will become violently ill.Pschological treatment is then used which is similar to heroin,counselling groupwork relapse prevention etc. Alcohol, heroin, cocaine,crack,ampthetamine abuse all have the same thing in common. They all destroy lifes and are incredibly difficult to stop using once you have created that dependency on them.
hope this helps.
own experience and training.