Wiktionary
a. Involving megadoses of vitamins.
WordNet
Wikipedia
Usage examples of "megavitamin".
For himself, he poured a glass of orange juice and downed a megavitamin, then rinsed the glass and left it in the drainer next to the sink.
They sell megavitamins, protein powders, and motivation magazines and tapes in there.
It was a simple and courageous move: yesterday I ceased all medication, not only the sedatives but the megavitamins and the antipsychotics.
I think you shot him up with the equivalent of megavitamins, minerals, body salts, antibiotics, you name it.
Now in retirement he seemed content to shepherd these older folk, plying them with megavitamins and morning Tai Chi exercises.
But vitamins A and D, when taken in the massive doses prescribed by megavitamin therapy, are stored in the body's fat complexes and can easily build to poisonous levels.