The World Anti-Doping Agency considers the heart disease medication a performance-enhancing drug and has banned it.
CAS upheld the Russian Anti-Doping Agency's decision to lift Valieva's provisional suspension on Monday, CNN reported. The court cited “exceptional circumstances” in its ruling Monday.
Trimetazidine is used to treat angina. The drug dilates blood vessels, allowing the heart to work more efficiently for longer.
Adults with angina can take trimetazidine. But it's not approved in the US. Beta blockers are more effective and have fewer side effects even where they are approved.