On April 20, 2010, he received a 50-game suspension for use of performance-enhancing drugs. Vólquez made his 2010 debut with the Reds on July 17, 2010, vs the Colorado Rockies with an 8–1 win. Vólquez held the Rockies to one earned run and three hits in six innings with 9 strikeouts and 2 base on balls. However, his next several starts were unimpressive, and for the second time in his career, he was demoted straight to single-A (the Dayton Dragons). He was recalled on September 7 and finished the season with a 4–3 record and 4.31 ERA over 62.2 innings. He started Game 1 of the 2010 National League Division Series against the Philadelphia Phillies and lost, allowing four earned over 1.2 innings with Roy Halladay throwing a no-hitter.