The FEI Anti-Doping Rules for Human Athletes (ADRHA)

As a Signatory of the World Anti-Doping Agency (WADA) Code, the FEI has developed Anti-Doping Rules for Human Athletes (ADRHA) in compliance with the Code as well as with WADA’s International Standards*.
On 1 January 2021 revised versions of the Code, International Standards and ADRHA came into effect.
In the FEI's ADRHA, specific requirements apply to "International-level Athletes". These are defined as follows:
1) Athletes ranked as listed below in the Ranking(s) applicable on 1 January for the year considered in any of the FEI disciplines:
    - Jumping: top 500 of the FEI Jumping World Rankings (Longines Rankings);
    - Dressage: top 300 of the FEI Dressage World Rankings;
    - Eventing: top 300 of the FEI Eventing World Rankings;
    - Para Dressage: top 100 of the FEI Para Dressage World Rankings;
    - Endurance: top 100 of the FEI Endurance World Rankings;
    - Driving: top 100 of the FEI Driving World Rankings;
    - Vaulting: top 100 of the FEI Vaulting World Rankings;
    - Reining: top 100 of the FEI Reining World Rankings
2) Athletes included in the FEI’s Registered Testing Pool (RTP) and/or Testing Pool (TP).

FEI Anti-Doping Rules for Human Athletes Library & References
The FEI Anti-Doping Rules for Human Athletes
The World Anti-Doping Agency (WADA)
The WADA Code 2021 (on the same page can be found the clean version, the redline from 2015 version, and a summary of the major changes from the Code 2015) 
WADA's Prohibited List effective 1 January 2021
WADA's International Standards