Like all the Special Equipment doctrines (with some exceptions - gotta love
GW's vagueness!
), you
must take Chem-Inhalers on all appropriate units. However, unlike the other four Special Equipment doctrines which refer specifically to Guard Infantry (and in some case Rough Riders), Chem-Inhalers has no restrictions.
This means that on the plus side you now have Ogryns with tough-as-nails Leadership rules, Stormtroopers who won't break, Ratlings who won't break even with their low
Ld, etc. etc. On the down side, however, you still
must the doctrine to everyone (i.e. every unit that isn't a vehicle), which will end up costing a lot.
So to answer your question (finally!),
yes, you
must give the doctrine to your Conscripts if you have taken the doctrine.