IMPORTANCERecent studies have yielded conflicting results as to whether testosterone treatment increases cardiovascular risk.OBJECTIVE To test the hypothesis that testosterone treatment of older men with low testosterone slows progression of noncalcified coronary artery plaque volume.DESIGN, SETTING, AND PARTICIPANTS Double-blinded, placebo-controlled trial at 9 academic medical centers in the United States. The participants were 170 of 788 men aged 65 years or older with an average of 2 serum testosterone levels lower than 275 ng/dL (82 men assigned to placebo, 88 to testosterone) and symptoms suggestive of hypogonadism who were enrolled in the Testosterone Trials between June 24, 2010, and June 9, 2014.INTERVENTION Testosterone gel, with the dose adjusted to maintain the testosterone level in the normal range for young men, or placebo gel for 12 months. MAIN OUTCOMES AND MEASURESThe primary outcome was noncalcified coronary artery plaque volume, as determined by coronary computed tomographic angiography. Secondary outcomes included total coronary artery plaque volume and coronary artery calcium score (range of 0 to >400 Agatston units, with higher values indicating more severe atherosclerosis). RESULTSOf 170 men who were enrolled, 138 (73 receiving testosterone treatment and 65 receiving placebo) completed the study and were available for the primary analysis. Among the 138 men, the mean (SD) age was 71.2 (5.7) years, and 81% were white. At baseline, 70 men (50.7%) had a coronary artery calcification score higher than 300 Agatston units, reflecting severe atherosclerosis. For the primary outcome, testosterone treatment compared with placebo was associated with a significantly greater increase in noncalcified plaque volume from baseline to 12 months (from median values of 204 mm 3 to 232 mm 3 vs 317 mm 3 to 325 mm 3 , respectively; estimated difference, 41 mm 3 ; 95% CI, 14 to 67 mm 3 ; P = .003). For the secondary outcomes, the median total plaque volume increased from baseline to 12 months from 272 mm 3 to 318 mm 3 in the testosterone group vs from 499 mm 3 to 541 mm 3 in the placebo group (estimated difference, 47 mm 3 ; 95% CI, 13 to 80 mm 3 ; P = .006), and the median coronary artery calcification score changed from 255 to 244 Agatston units in the testosterone group vs 494 to 503 Agatston units in the placebo group (estimated difference, −27 Agatston units; 95% CI, −80 to 26 Agatston units). No major adverse cardiovascular events occurred in either group.CONCLUSIONS AND RELEVANCE Among older men with symptomatic hypogonadism, treatment with testosterone gel for 1 year compared with placebo was associated with a significantly greater increase in coronary artery noncalcified plaque volume, as measured by coronary computed tomographic angiography. Larger studies are needed to understand the clinical implications of this finding.

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