Depending on the substance you come in on the detox procedure is different for each individual person.
If you are on any type of opiates like heroin, or prescription medication like Tramadol, or Co-dydramol the detox can last for up to 28 days . With heroin you will be brought down slowly with Methadone or Subutex, also known as Buprenorphine. Most treatment centres will give you a blind detox, and you will not know the dose you are on. The first 3 days you will feel uncomfortable but after this the detox will be much more bearable. When you are coming off prescription medication they will just lower the does daily to bring you down in a safe way.
Alcohol can take between 5 to 10 days. You will be prescribed Librium and Vitamin B tablets.
Crack Cocaine is more an obsession of the mind, so there isn’t really much that can be given, but some treatment centres will give a short course of Benzodiazepine to get you settled in to your process.
Benzodiazepine has to be a very slow process and can take up 28 days to detox from.