The drug that has produced more than 100 positive doping tests since being outlawed on January 1 can take "several months" to completely leave the body, claims the manufacturer.
A number of athletes, including tennis superstar Maria Sharapova, say they took cardiac drug meldonium before it was banned by the WADA.
Latvian manufacturer Grindeks said in a written statement to Reuters that meldonium has a half-life of between four and six hours but "its terminal elimination from the body may last for several months" depending on a variety of factors such as dose, duration of treatment, and sensitivity of testing methods.
Meldonium has been in the spotlight since Sharapova stunned the sporting world by announcing earlier this month that she had failed a doping test for the drug after a loss to Serena Williams at this year's Australian Open.
Sharapova, who is provisionally banned while the International Tennis Federation (ITF) investigates, said she had been taking the drug for 10 years for health reasons and had not realised it had been recently placed on WADA's banned list.
While meldonium, which is marketed as Mildronate, was developed to treat heart conditions such as angina, it was also used extensively for three decades to toughen up Soviet troops in action at high altitude.
WADA banned it, citing mounting evidence of its performance-enhancing benefits and widespread use in sport.
Former WADA chief Dick Pound said this month that there was an awareness in "tennis circles" that meldonium use was prevalent -- a claim dismissed by the ITF.
At least 16 Russian sportsmen and women, speed skating Olympic gold-medallist Semion Elistratov, have been caught using meldonium since the ban came into effect.
On Monday Russia's athletics chief said four track-and-field athletes had tested positive, adding further scrutiny to a nation currently banned from international track-and-field competitions after last year's revelations of widespread cheating and corruption.
