Stress axis (HPA)

Phosphatidylserine (PS) is a membrane phospholipid sold for memory. The strongest early trial used PS extracted from cow brain, in 494 elderly patients with cognitive decline. Soy-derived PS, developed as an alternative to bovine PS, has smaller trials showing memory gains in older adults with memory complaints. Smaller studies suggest it blunts the cortisol response to stress.

Rhodiola rosea is an Arctic and alpine herb marketed as an adaptogen for stress and fatigue. Some randomised trials report less mental fatigue, but one found it made fatigue worse. Systematic reviews describe the evidence as contradictory and the trials as poorly reported.