Sort of pill that gives 50 p.c. vigour before half a minute? (7)
I believe the answer is:
vitamin
But I can't explain it at all! Could you help me understand?
(Other definitions for vitamin that I've seen before include "Riboflavin, for example" , "Organic substance essential to life" , "Tim, Ivan (anag)" , "A, B, C, D, E or K" , "Essential substance in food" .)