The Gut-Brain Axis
The vagus nerve carries signals bidirectionally. 95% of serotonin is made in the gut. Over 40 RCTs have tested specific strains for anxiety.
Strains With Evidence
- B. longum 1714: Reduced cortisol in 2016 RCT
- L. helveticus R0052 + B. longum R0175: 36% anxiety reduction (n=55)
- L. plantarum PS128: Improved ASD behaviors in children
Why Most Probiotics Won't Help
Effects are strain-specific. L. rhamnosus GG (most common) has zero anxiety evidence — it's a different strain than L. rhamnosus JB-1.
The Bottom Line
Psychobiotics are real but you need the right strain. Generic probiotics for anxiety is like random antibiotics for a specific infection.