The most appropriate answer in this scenario is B. amphetamines.
Amphetamines can increase physical performance and provide a temporary boost in energy, which may explain why the runner is running quicker. However, they can also lead to negative side effects such as fatigue, mood changes, and depressive symptoms as the effects wear off. The other options (growth hormones, protein supplements, and creatine) don't typically produce the same rapid energy boost or significant mood changes in the way that amphetamines can.