First Human Phase 1 Trial Finds Low-Dose Mitragynine Enhances Attention, High Dose Causes Amnesia

Why it matters

This is one of the first controlled human trials of isolated mitragynine, providing clinicians and regulators with direct evidence of dose-dependent cognitive effects rather than relying solely on animal models.

The big picture

Despite widespread kratom use — estimated at 2–16 million Americans annually — controlled human trials have been nearly absent. This exploratory Phase 1 study fills a critical gap by testing single oral doses (5–40 mg) of isolated mitragynine in 15 healthy volunteers, measuring vital signs, subjective experience, neurocognition, and pain tolerance over 7 hours.

Key findings

• Low doses (5 mg) increased subjective arousal and attention and improved accuracy on a sustained-attention task
• The 5 mg dose also enhanced motor inhibition, suggesting stimulant-like effects at lower amounts
• The highest dose tested (40 mg) produced subjective feelings of amnesia and mild psychopathological symptoms
• Vital signs were not significantly affected at any dose tested
• All doses up to 40 mg were well tolerated with only mild, transient side effects reported

What they say

The researchers concluded: "Low doses (5–10 mg) of mitragynine may cause subjective feelings of stimulation and enhance attention, while the highest dose (40 mg) may cause inhibitory feelings of amnesia and distress."

Bottom line

**The first controlled human trial of isolated mitragynine confirms dose-dependent effects: stimulant-like at low doses, sedating and mildly psychopathological at high doses — with vital signs remaining stable throughout.**