In this post, Ray Peat presents serotonin not as a "happiness hormone," but as a stress-related signal that helps organisms cope with adverse conditions by slowing metabolism, conserving energy, and suppressing activity. He argues that many of serotonin's effects resemble those seen in hibernation and other defensive physiological states, where survival is prioritized over growth, repair, and optimal function.

According to Peat, excess serotonin contributes to a wide range of conditions, including migraines, anxiety, depression, cardiovascular disease, dementia, and age-related degeneration. He argues that serotonin impairs mitochondrial energy production, interferes with glucose metabolism, increases stress hormones, and promotes chronic inflammation. In this view, many diseases are manifestations of impaired cellular energy production rather than isolated defects in specific organs or neurotransmitter systems.

Peat stresses the relationship between serotonin, gut health, hormones, and metabolism, and argues that intestinal irritation, endotoxin exposure, hypothyroidism, excess dietary tryptophan, and polyunsaturated fats can all increase serotonin activity. While his recommendations often included fruit sugars, honey, and juice to support thyroid function and reduce stress hormones—a point that differs from the MetFix emphasis on carbohydrate restriction—both perspectives share the broader view that chronic disease is fundamentally a problem of impaired metabolism and mitochondrial dysfunction. Ultimately, Peat presents serotonin as part of a larger stress-response system linking inflammation, aging, hormonal regulation, and metabolic health.