The Medicine skill determines how many Hit Points you’ll replenish upon using a Stimpak, and the effectiveness of Rad-X and RadAway.

This skill, for all its apparent worth, can be ignored. There is always another way of handling a situation, from donning an Environmental Suit, to visiting a doctor, to just using more Caps. It’s more useful in Hardcore mode to be able to ignore these inconveniences, but in a normal game you don’t really need a high Medicine score. That said, there are a good number of Medicine challenges in this game, so from a story aspect it’s not entirely bad to splurge a little extra.