Quintana, a former Giro d'Italia and Vuelta a Espana winner, finished sixth in the general classification and was disqualified after analysis of two dried blood samples revealed the presence of tramadol and its two main metabolites.
The 32-year-old has denied using tramadol, which is prohibited under the UCI's Medical Rules but banned only in competition. Its usage does not qualify as an anti-doping violation.
It does not feature on the World Anti-Doping Agency's list of prohibited substances but will be banned by the body in 2024.
"The panel deliberated and determined that the UCI's in-competition ban on tramadol was for medical rather than doping reasons and was therefore within the UCI's power and jurisdiction," CAS said.
"Furthermore, the Panel was comfortably satisfied that the scientific evidence showed that Nairo Quintana's samples contained both tramadol and its two metabolites. On this basis, the panel concluded that the challenged decision should stand, and dismissed the appeal."
Quintana, a three-time Tour de France podium finisher, withdrew from this year's Vuelta in August and left his Arkea-Samsic team last month.
