Some classes of drugs and techniques are banned from sports globally. However, during cough, cold and allergies, WADA has prescribed few drugs that are permitted to be consumed by athletes.
There are few drugs or techniques, which comes under the category of doping and are banned from the Olympics. They are:

Anabolic drugs like steroids and testosterone

Hormones and Growth Factors

Diuretics and Masking Agents

Oxygen Transfer Enhancements

Physical and Chemical Manipulation

Stimulants

Narcotics

Alcohol

Cannabinoids

Beta Blockers.
In case of cough, cold, flu or other allergic cases, the athletes are permitted to take only those medicines that are prescribed safe by WADA. Vicks Vapor inhaler is prohibited from use since it contains levmetamfetamine, which acts as a stimulant. Several other cough syrups and analgesics are prohibited from the athletic events.