pro·drug 
(prōdrŭg′)
(prōdrŭg′)n.
Any of various drugs that are administered in an inactive form and converted into active form by normal metabolic processes.
- under lock and key
- underlying
- undermine
- undermodulate
- undermodulation
- undermost
- underneath
- under no circumstances
- under nose
- undernourish
- undernourishment
- undernutrition
- under oath
- under (one's) belt
- under one's belt
- under (one's) breath
- under one's breath
- under (one's) hat
- under one's hat
- under (one's) wing
- under one's wing
- underpaid
- under pain of
- underpants
- underpart