An injected decoy protein that soaks up the body's own brakes on muscle growth. It enlarged muscle in both human trials, and also raised bone density and reduced body fat, without any matching gain in strength or walking ability. Development stopped over clusters of widened small blood vessels and nosebleeds. Nearly every vial tested contained a different protein entirely. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Hematocrit | 40–48% (men), 36–44% (women) | Detects the red-cell rise seen with this class |
| Hemoglobin | 13.5–16.0 g/dL (men), 12.0–14.5 g/dL (women) | Confirms a hematocrit shift is real erythropoiesis |
| Platelet count | 200–350 × 10⁹/L | Shows whether vessel fragility becomes bleeding |
| Ferritin | 50–150 ng/mL | Tracks iron drawn down by red-cell production |
| Blood pressure | Below 120/80 mmHg | Higher pressure amplifies small-vessel bleeding |
| Lean body mass (DXA) | No established target; % change from own baseline (trial gains 3–5%) | The only outcome shown to move in humans |
| Lumbar spine bone mineral density (DXA) | T-score above -1.0 | Captures the bone effect alongside muscle gain |
| ALT | 10–26 U/L (men), 7–22 U/L (women) | Baseline organ safety and concurrent substances |
| eGFR | Above 90 mL/min/1.73 m² | Baseline organ safety before an unlicensed drug |
Cadence: Blood work and blood pressure at 4 weeks, then every 8–12 weeks; skin and mucosal inspection weekly; DXA at 12 and 24 weeks.