The five-time Grand Slam champion had accepted a one-month suspension in November after testing positive for TMZ in an out-of-competition sample in August which was caused by contamination of her medication melatonin.
Swiatek had said she had been taking it for jet lag and sleep issues and did not receive a lengthy ban after the International Tennis Integrity Agency (ITIA) ruled there was no significant fault or negligence on her part.
"WADA has conducted a full review of the case file related to the ITIA decision, which it received on November 29th," WADA said in a statement.
"WADA's scientific experts have confirmed that the specific contaminated melatonin scenario, as presented by the athlete and accepted by the ITIA, is plausible and that there would be no scientific grounds to challenge it at CAS."
Swiatek said anyone who knew the details of her case would be understanding.
"The locker room has also been pretty nice," she added.
"The girls are understanding... Now for sure, I just want to put this behind me, because I have already been on tour for quite a few weeks, and it's all been good.
"I don't expect any changes. I'm happy people understand."
Men's world number one Jannik Sinner is still under the scanner after testing positive for anabolic agent clostebol. The Italian was also cleared of wrongdoing but WADA lodged an appeal to the CAS, with a hearing starting on April 16th.