Some substance categories and methods are prohibited during both the in- and out-of-competition periods, that is, all year. Other substance categories are only prohibited during an in-competition period.
The substances which are prohibited at all times includes masking agents and those substances which, when used in training, may have long-term performance-enhancing effects, such as anabolic steroids.
Unless otherwise stated, the in-competition period begins 12 hours before a competition which the athlete is participating in and finishes at the end of any associated testing. An athlete should not have any prohibited substance in their system during that time. Some events may declare a different in-competition period. For example, at the Olympic Games the IOC declares that in-competition testing for all sports can take place from the opening to the closing of the athlete village, which is a period of around a month and even includes once a sport has finished all competition. Athletes should check with their NGB, IF or event organisers how their in-competition is defined.