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. Caffeine will then have a more pronounced effect in boosting performance. Taking aspirin or ibuprofen is a common practice in ultras. It is not illegal or against the rules to use these items.