The immune system is weakened, thus consuming antioxidants will help ward off potential illness that sometimes follows an ultra effort. Taking vitamin C, E and beta carotene can help neutralize the free radicals that are produced when exercising or running extremely long distances. Free radicals are unstable molecules that can cause muscles to be further damaged, as well as a weakening the immune system. Amino acid supplements should in theory keep you more anabolic, versus catabolic, a state in which the body begins to break down. I have also seen people stage miraculous recoveries during the night of 24-hour runs, who, after consuming exclusively carbohydrates, have taken protein or amino acid supplements, then suddenly sprung to life.
Caffeine is a drug found often in drinks.
Colas and coffee are quick acting and can bring new life into a runner. Some studies have shown that caffeine stimulates the central nervous system, boost adrenaline levels and promotes fat burning. Caffeine can also be detrimental in that it is a diuretic, causing water loss. Moderate doses of caffeine can boost performance, but overuse can be detrimental. Decreasing dependence on caffeine can be done in a matter of days through abstinence.