Mitragynine and 7-hydroxymitragynine
Kratom's Most Famous Alkaloids Side-by-side
For those looking for pain relief, relaxation, or energy, the alkaloids, mitragynine and 7-hydroxymitragynine, are usually the most important elements of the kratom leaf. Mitragynine is present in much higher concentrations than 7-OH-mitragynine – an average of 66% of total alkaloid content versus roughly 2%, respectively. That said, the 7-hydroxy version is about 46 times stronger than the other and up to 13 times more potent than morphine by weight.
Here’s where it gets a little more complex – please pardon the increased scientific speak for a moment. If you remember anything from chemistry class, you may recall that polarity influences the ability of molecules to pass through lipids. The hydroxy group present in 7-OH-mitra makes it more polar than mitragynine. High polarity means greater difficulty in crossing the blood-brain barrier.
The blood-brain barrier is a natural protection mechanism built into the capillaries inside the brain and designed to keep things like toxins and pathogens out while allowing beneficial substances in, though its accuracy in judgment is not perfect. The lower relative polarity of mitragynine makes it able to cross the blood-brain barrier at a rate around 10 times higher than that of 7-hydroxymitragynine, which is compounded by the former’s superior uptake by the brain.
A 2019 study found that mitragynine was actually more effective than the 7-OH version when consumed orally. That said, the study also found that mitragynine exhibits its analgesic actions as a result of the body converting it to 7-hydroxymitragynine. Once the substance is ingested, the body’s P450 enzymes effectively oxidize one into the other at a rate that would explain kratom’s activity atthe mu-opioid receptors.
This is actually a microcosm of what happens when red kratom is made. After naturally green leaves are dried they are set out in the sun to cure for even longer, which speeds up the oxidation process. The color red is a result of oxidation and can be indicative of greater 7-OH-mitragynine content.
This should all be taken with precaution, however. Most studies are performed either with rats or in vitro (in petri dishes) with cells from human tissue. What would be very useful are actual human studies, which may come as kratom is explored further in academia.
What we know for sure is that the combination of mitragynine and 7-hydroxymitragynine is responsible for the vast majority of the leaf’s pain relieving properties. It also achieves this without recruiting beta-arrestin pathways, which means there is little threat of respiratory depression unlike we see with opioids. The world of kratom research is still young and, with its popularity increasing, there is probably going to be a great increase of available literature moving forward.