'Addictive' would be the natural choice for me:
Heroin is addictive.
I have, however, seen 'addicting used in this context- 'addicting computer games'.
However, if the addiction were forced, you could say the following:
Addicting someone to heroin is an appalling thing.
The 'addictive' form would refer to the thing that has the potential to make someone addicted, whether they tale it or not, while 'addicting' would refer to the process, so it has a more restricted meaning. 'Addicting' is also uncommon:
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