Balsalazide-azo-bonded prodrug, activated by bacteria in the colon

Prodrug for Phenobarbital.

A prodrug is a drug that is inactive when you take it (when it is administered), but then becomes active once your body starts to break it down (usually through metabolism). Stimulant simply refers to a class of drug. The opposite would be a non-stimulant. However, it is a different adjective describing the drug and is not part of "prodrug". That is, to be clear, the drug you're looking at is both a stimulant and a prodrug.

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prodrug

If the base hydrolysis mechanism is important, an electron withdrawing group can be attached to the prodrug. If the acid hydrolysis mechanism is important, an electron donating group can be attacked to the prodrug.