Complex sentence: Diamorphine is also used as a maintenance drug to treat certain groups of addicts, normally long-term chronic intravenous (IV) heroin users, and even in these situations it is only prescribed following exhaustive efforts at treatment via other means.
Split into simpler sentences: Diamorphine is also used as a maintenance drug to treat addiction, normally in long-term chronic intravenous (IV) heroin users. It is only prescribed following exhaustive efforts at treatment via other means.