Mitragynine

Mitragynine is the most abundant psychoactive alkaloid in the leaves of kratom (Mitragyna speciosa), a Southeast Asian plant. It is the compound primarily responsible for kratom's effects, and it is the substance regulators and researchers focus on when studying the plant. Mitragynine occurs naturally in the leaf and is also discussed in its isolated form. In the body it is partly converted into a second compound, 7-hydroxymitragynine, which is much more potent at opioid receptors. Because most people encounter mitragynine by using kratom rather than as a purified chemical, its overall effects, uses, and risks closely track those described for kratom itself.

Mitragynine has a mixed and somewhat atypical pharmacology. It acts as a partial agonist at the mu-opioid receptor while interacting differently with other opioid receptor subtypes, and it also engages adrenergic and serotonergic receptors in the central nervous system — a combination thought to explain why lower doses can feel stimulating while higher doses feel more opioid-like. Importantly, research indicates that much of mitragynine's opioid effect comes after the body metabolizes it (via a CYP3A pathway) into 7-hydroxymitragynine, which binds mu-opioid receptors far more strongly. Some studies suggest mitragynine and its metabolite may be 'atypical' opioids that produce pain relief with less respiratory depression than classic opioids, but this is still an active area of research and does not mean they are free of opioid risks.

Because mitragynine is the principal active compound in kratom, its effects mirror kratom's and are dose-dependent: lower doses are associated with stimulant-like alertness and energy, while higher doses produce opioid-like sedation, pain relief, and euphoria. Commonly reported side effects include nausea, vomiting, constipation, itching, sweating, dizziness, and dry mouth. With repeated use, tolerance and physical dependence can develop, and stopping can produce opioid-like withdrawal.

Mitragynine carries the same core risks as kratom: dependence, withdrawal, and the dangers of combining an opioid-acting substance with other depressants such as opioids, benzodiazepines, or alcohol, which can increase sedation and the risk of slowed breathing. A central safety issue is its metabolite and relative, 7-hydroxymitragynine: while 7-OH is present only in trace amounts in natural leaf, concentrated or semi-synthetic 7-OH products are far more potent, behave much more like strong opioids, and carry correspondingly higher risks of dependence, overdose, and respiratory depression. Reported harms linked to kratom alkaloids include liver injury, seizures, and rapid heart rate. If someone may have overdosed or taken a dangerous combination, call 911; for poisoning call Poison Control at 1-800-222-1222. For help with dependence, SAMHSA's helpline is 1-800-662-4357.