You need to carry them.
You must give him five Stimpaks or you can give him three Buffouts. It is said that the Taft Tunnels contain enough Buffout and Stimpaks to be found and given to Garza. You can also by passing a speech check, leave him and let him die. He doesn't play anything important for the game after The Waters of Life, so it doesn't matter much if you leave him to die or save him. You can also simply kill him, this shouldn't turn the followers hostile, instead you are talked to by the disgusted Dr. Li.