The objective of the question is to identify which of the given substances is not banned by the International Olympic Committee (IOC). To answer this, we need to understand the IOC's stance on drugs and substances used in sports.

The IOC, in collaboration with the World Anti-Doping Agency (WADA), enforces a strict prohibition on substances that can enhance athletic performance, harm athletes, or violate the spirit of sport. Here is a breakdown of each option to determine which one is not banned:

1. Cocaine: This is a powerful stimulant and is prohibited under WADA's list as it can enhance performance and is harmful to health.
2. Marijuana: Although the debate continues due to its varying legal status around the world, marijuana is generally prohibited in competition by WADA because it can affect performance, risk safety, and violate the spirit of sport.
3. Ephedrine: This is a stimulant and is present on the WADA Prohibited List due to its potential for enhancing performance and its risk to athletes' health.
4. Alcohol: Traditionally, alcohol has been banned in a few specific sports where its consumption would pose an immediate risk, such as shooting sports. However, it is not generally banned across the board by the IOC/WADA.

From the analysis above, alcohol is not universally banned by the IOC, making it the correct answer among the provided options.

Thus, the correct answer is:

Alcohol