It is VERY common for professional athletes to have exemptions, especially for conditions such as allergy and asthma. For example, the world champion in cross country skiing (an endurance sport) has an exemption for an asthma medication that is known to improve endurance. It is considered to level the playing field when you have a diagnosed condition.
from the WADA site:
"The World Anti-Doping Code (Code) recognizes the right of athletes to the best possible treatment for any medical condition. If you are in need of medication, please contact your International Federation or NADO to find out more about the criteria and procedures to apply for a Therapeutic Use Exemption (TUE)."