What it's actually good for
Citrulline malate occupies a useful niche in sports supplementation. L-citrulline is converted to L-arginine in the kidneys, which then feeds into nitric oxide production — and it does this more effectively than supplementing with arginine directly, because citrulline bypasses the extensive gut and liver degradation that limits oral arginine's bioavailability. The practical result is improved blood flow, reduced arterial stiffness, and a modest but measurable boost to exercise performance.
The strongest evidence is for resistance training: multiple studies show that 6-8 g of citrulline malate before a workout increases the number of reps you can perform before failure and may reduce post-exercise soreness. The effects are real but moderate — expect a few extra reps per set, not a transformation. For aerobic exercise, the data is less consistent. On the cardiovascular side, meta-analyses support small but significant reductions in blood pressure, particularly in populations with elevated baseline levels. This earns a B grade: the mechanistic pathway is well-understood, the human data is generally positive, but effect sizes are modest and study quality is mixed.