The 24-year-old, who won 200m breaststroke bronze at the London 2012 Olympics, was given a provisional ban after testing positive for meldonium.
The International Swimming Federation (Fina) lifted the ban after advice from the World Anti-Doping Agency (Wada).
Meldonium is the substance Russian tennis player Maria Sharapova tested positive for earlier this year.
A statement from Fina read: "Wada is to undertake further scientific research on meldonium and have therefore recommended to Fina that the suspension of the swimmer should be lifted."
However, Fina also said the case "is not closed" and a decision will be made "following the outcome of Wada's studies".
The statement added: "After that, Ms Efimova would be entitled to file an appeal to the Court of Arbitration for Sport."
Efimova is facing a life ban having previously tested positive for a banned substance.
The American-based swimmer was banned for 16 months by Fina after traces of the anabolic steroid DHEA (dehydroepiandrosterone) were found in her system at an out of competition test in Los Angeles in 2013.
Wada added meldonium to its list of banned substances at the start of 2016 and recently gave those athletes who had since failed tests a lifeline with the admission it was unclear how long the substance took to clear the body.
Russia's Yulia Efimova has had her provisional suspension for doping lifted by swimming's governing body.