What it's actually good for
Phosphatidylserine (PS) is a phospholipid that is a major component of cell membranes, particularly abundant in brain tissue where it plays a role in cell signaling, neurotransmitter release, and synaptic function. The cognitive evidence is strongest in older adults experiencing age-related decline: multiple RCTs have shown improvements in memory, attention, and verbal fluency at doses of 100-300 mg/day, leading the FDA to allow a qualified health claim (with the important caveat that evidence is "limited and not conclusive"). A separate line of research has examined PS for cortisol modulation, with several studies showing that higher doses (400-800 mg/day) blunt the cortisol spike following intense exercise. This earns a B because the cognitive data, while positive, comes mostly from older populations with existing decline and the landmark early studies used bovine-derived PS, which is no longer available. The plant-derived PS used in modern supplements appears to work similarly, but fewer large RCTs have been conducted with these newer forms. For healthy younger adults looking for a nootropic boost, the expected benefit is modest at best.