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1.
Ibuprofin, an anti-inflammatory. Used to such a great extent by many athletes that it can be considered to have a DRI of 400-800 mg much like a real vitamin.
Oh man, my shins are killing me, time to pop some vitamin I.
by Seth March 04, 2004
 
2.
Ibuprofen, a non opiate, non steroidal, anti-inflammatory drug
After the surgery they gave me a prescription for Vitamin I, but it was for a higher dose than is available over the counter.
by The Return of Light Joker September 10, 2011
 
3.
A subtle word (often used as a code word) to describe one or more attractive persons in a place, surrounding, or area.
*At a party* (person 1): "is there any 'vitamin I' around here?"
(person 2): "Only one source of vitamin I. He's standing by the door... Blonde hair, blue eyes, Irish..."
by Kris-Jen October 10, 2011
 
4.
This vitamin probably exists somewhere in the real world, but for now it can mean "heals all heartbreak" or something wonderfully tragic like that.

See heartbreak.
You got your heart broken? Try some vitamin i. It helps. Sometimes.
by cuhlare November 16, 2006