Answer:
The problem with opiates is that, due to the artificial scarcity created by prohibition, they are artificially expensive. Since the average person cannot long support a habit by working, they end up turning to crime.
For an addict, all opiates are interchangeable. That is, any opiate will do the job of making you "well." In other words, if you are addicted to oxycodone, heroin will do just as well.
So, replacement drugs are simply a different opiate - methadone or buprenorphine - which have the benefit of being longer-acting than recreational opiates, (one dose every twenty-four hours rather than four doses per day). They also have the benefit, at least from the moralist's perspective, of not getting you high. This is because the shorter-acting an opiate is, the more euphoria it provides.
Since these replacement opiates are obtained legally, they are much less expensive, (although still over-priced), than those obtained on the black market. Since opiates do not harm the body, and since opiates do not impair the user, being able to obtain them legally allows the user to "get their life back." That is, they can hold down a normal job.
There are no "replacement drugs" for non-opiates. I think it's worthwhile to make a distinction here, because the word "addictive" gets thrown around pretty loosely these days.
Opiates are addictive. If you take them long enough - everyday for a month - when you stop, you will become very ill.
Other drugs are compulsive. If you used cocaine or speed everyday for a year, then stopped, you would not become ill.
It is possible that certain other drugs, such as barbiturates and benzodiazepines are addictive in the same sense as opiates, but I am not too clear on that. Again, no clear distinction is made these days, and anything people do to excess is called an addiction.
Step-by-step explanation: