What USADA says:
Substances and Methods Prohibited In-Competition
This section focuses on substances that are prohibited only in-competition. These substances may be used when athletes are not competing. USADA does not test for these substances out-of-competition. It is very important to be aware of the definition of “in-competition.” Each International Federation may have a different definition of “in-competition” and it may vary by event. For some events, “in-competition” may be defined as “12 hours before the start of the competition” and different rules may apply to multi-day events (for example, the Olympic Games). It is very important for athletes to understand the definition of “in-competition” for the sporting events in which they compete. Athletes must ensure that all substances prohibited in-competition have completely cleared from their body before competition. If this is not possible, or if the chronic use of one or more of these medications is needed, the athlete should apply for a Therapeutic Use Exemption.
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S8. Cannabinoids
Natural or synthetic tetrahydrocannabinol (THC) and THC-like cannabinoids (e.g. hashish, marijuana, HU-210) are prohibited.
Advisory:
1. Athletes should be aware that cannabinoids may be retained in fat tissue following chronic use and may be detected weeks after use. There have been situations where sudden weight loss has caused cannabinoid metabolites stored in fat to be released in detectable levels. USADA strongly advises athletes not to use cannabinoids at any time.
http://www.usada.org/prohibited-list/athlete-guide/
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