Beijing: British tennis star Andy Murray said on Tuesday that the World Anti-Doping Agency made "mistakes" over how it handled the ban on the drug meldonium, allowing athletes to escape suspensions.
A number of athletes have since tested positive for meldonium since it was added to WADA's list of banned substances on January 1 -- the most high profile five-time woman's Grand Slam champion and highest earning female athlete Maria Sharapova.
But the anti-doping body issued a statement in April saying that it did not know for sure how long it takes meldonium to leave the body.
That grey area has allowed athletes across numerous sporting disciplines to escape suspension unless it can be proved they took the medication during 2016, after it was banned.
Sharapova had her two-year tennis ban for doping reduced to 15 months by the Lausanne-based Court of Arbitration for Sport (CAS) on Tuesday.
"You could understand if it was reduced," Murray said, referring to Sharapova's two-year ban.
"It's a difficult situation because I think WADA obviously made some mistakes with the substance, with meldonium," he told reporters a few hours before the CAS verdict was released.
"A lot of athletes were let off because they (WADA) didn't know how long the substance stayed in the system for," the double Olympics gold medallist and three time Grand Slam champion added.
Murray has been very outspoken on dopping issues and slammed one of his main sponsor's, tennis racket manufacturer Head, for standing by Sharapova when she admitted taking meldonium.
Sharapova tested positive for meldonium during January's Australian Open and admitted to taking it during that tournament, after it was added to the banned substance list.
Meldonium has been used to treat heart disease and diabetes but also increase blood flow so can enhance athletic performance. (ALSO READ: Andy Murray says he was stalked by a hotel maid)
American tennis player Varvara Lepchenko was exonerated of any wrongdoing in September after testing positive for meldonium.
WADA said the decreasing amounts of meldonium in the 30-year-old Uzbek-born player's samples was consistent with her account that she only used the medication prior to it being added to the banned list at the start of the year.
Russian swimmer Yulia Efimova was provisionally suspended by the swimming governing body FINA in March after a positive test for the drug.
As a two-time offender she faced a lifetime ban, but FINA lifted the suspension in May after WADA issued the statement saying it was unsure about how long the substance takes to leave the system.