Comprehensive Review: Kratom's Two Key Alkaloids Show Broad Pharmacological Potential With Distinct Opioid Profiles

Why it matters

Mitragynine and 7-hydroxymitragynine have been studied across 150+ papers, but this 2025 review is the first comprehensive synthesis — and it reveals that 7-OH binds opioid receptors 13× more potently than morphine while highlighting major research gaps in lesser-studied alkaloids.

The big picture

As regulatory debates intensify around 7-hydroxymitragynine specifically, this review underscores how much remains unknown — particularly about lesser alkaloids that may have therapeutic value without the same abuse liability concerns driving current policy battles.

Key findings

• • 7-hydroxymitragynine binds opioid receptors with 46× more affinity than mitragynine and 13× more than morphine, explaining its outsized potency relative to its low natural concentration (0.02–2% of leaf)
• • Both alkaloids have demonstrated analgesic, anti-inflammatory, anti-anxiety, anti-cancer, and antimicrobial activities across reviewed studies
• • Most research has focused exclusively on leaves; flowers and other plant parts remain largely unstudied
• • Current extraction protocols are costly and time-consuming, limiting broader independent research
• • Some minor kratom alkaloids appear to exhibit superior pharmacological activity to the two main compounds but remain significantly understudied

What they say

Systematic literature review of 150 papers published from 1921–2024, sourced from PubMed, ScienceDirect, and Google Scholar; International Islamic University Malaysia and collaborating institutions, Kuwait Journal of Science, 2025.

Bottom line

This review consolidates a century of kratom alkaloid research while highlighting where science needs to go next — particularly on lesser-studied alkaloids and plant parts that could unlock new therapeutic applications.