Retatrutide Weight Loss Truth

Brad systematically deconstructs the phase 3 trial of retatrutide, contrasting it with published trials of semaglutide and tirzepatide. He explains that the 28.7% weight loss widely cited is a per-protocol efficacy estimate, not the more practical treatment-regimen estimate (23.7%). When compared to tirzepatide's treatment-regimen 20.9% after 72 weeks, the advantage is minimal. Moreover, the side-effect profile is worse: nausea/diarrhea similar to semaglutide but higher than tirzepatide, and a novel 21% dysesthesia rate. The 18% dropout rate also signals poor tolerability. He concludes that, given current evidence, tirzepatide should remain the preferred choice. Only if a patient fails to achieve adequate weight loss with tirzepatide might retatrutide be considered—and only after more safety information is available. He explicitly states he would not choose it first-line.

Brad distinguishes between the 'efficacy estimate' (per-protocol, assuming perfect adherence) and the 'treatment regimen estimate' (includes dropouts and non-adherence). The publicly promoted 28.7% number came from the efficacy analysis, while the more realistic and commonly used primary endpoint—treatment regimen—was 23.7%. When he compares apples to apples, tirzepatide's treatment-regimen result was 20.9% after 72 weeks, retatrutide's was 23.7% after 68 weeks. The gap shrinks to less than 3 percentage points. He stresses that this small difference makes him question whether the added side-effect burden is worthwhile. He's waiting for the full published study to confirm these rates and additional safety signals.

Brad notes that while common GI side effects like diarrhea were similar between semaglutide and retatrutide (and lower with tirzepatide), dysesthesia stands out. The phase 3 trial report described symptoms as generally mild, but he emphasizes that a rate of 21% means 1 in 5 patients experienced this unsettling sensation. He points out that we haven't yet seen the full adverse event data, and earlier phase 2 data showed heart rhythm abnormalities. The combination of these signals leads him to conclude that the side-effect burden may outweigh the limited extra weight loss. He urges caution and further investigation before routine use.

Brad acknowledges the study's note that baseline BMI correlated with dropout—patients with lower BMI were more likely to stop, perhaps because they reached a weight they considered sufficient. However, even among those with a BMI of 35 or above, the discontinuation was 12.1% at the higher dose, still substantially higher than tirzepatide's 7%. He suggests that side effects, not just over-successful weight loss, drove much of the dropout. With such a high rate, real-world effectiveness will be diminished, further narrowing any advantage over tirzepatide. This supports his overall caution and preference for tirzepatide first.