Level of severity and types of withdrawal symptoms experienced can be very individual. A user consuming more each day will tend to have more severe symptoms than a friend using less, but gender, age, state of physical and mental health, and many other thing can affect this. Withdrawal symptoms include aches and pains, sweating, itches, sneezing, sleep disturbances, hallucinations in cases of heavy use, and vomiting and nausea. These drugs simply maintain your habit, and withdrawal will be experienced if you stop using them straightaway, same as with heroin. They can be very important, providing people with a way of functioning without heroin, but prescription diacetylmorphine could meet this role just as well.
Naltrexone is a drug which blocks the effects of opiates.
If you have already withdrawn from heroin you can take this drug and you will not be able to feel the effects of any heroin you take. The theory here is that you won't buy heroi if you can't feel it. The drugs effect only lasts 48 hours, so some users choose when to take Naltrexone, and when to stop so that they can use in a few days time. In smaller doses many users find that heroin stimulates libido, and increases sensuality and connection with a partner. Orgasm is generally more difficult to achieve, but this can prolong the sexual act and enjoyment.