I would vote for both varieties of mushrooms from the Super Mario Bros franchise, which if you think about it would have fantastic applications in medicine, cosmetics, etc if ground up and carefully administered in the correct doses!
A small dose of the Power Mushroom could be ingested to boost someone's height considerably (without going to the extreme of doubling it as a whole mushroom would), or be applied externally as part of a cream onto targeted areas to adjust proportions. (Both of which would be vastly preferable, and less invasive and dangerous, than the real-world cosmetic surgeries to increase height and/or body part sizes.) Moreover, the Power Mushroom seems to make one more impervious to pain--given that the player can take an extra hit before dying within the game.
The medicinal benefits of 1-Up Mushrooms are obvious and extreme, even if we were to replace the concept of extra lives to spare with a resurrection effect similar to Final Fantasy's phoenix downs.
Both would-and-should be well stocked in every hospital and pharmacy, although they wouldn't be available over-the-counter as they would clearly be categorized and regulated as extremely powerful and effective drugs.