The primary alkaloid by far in Kratom leaf is Mitragynine, and indeed Kratom products are typically rated by how much Mitragynine they contain. However, Kratom has dozens of other alkaloids, all of which play an important role in Kratom’s effects, and one of the most important of these alkaloids is 7-hydroxymitragynine, despite the fact that 7-hydroxymitragynine is found in very low concentrations in Kratom leaf.
In general potent and fresh Kratom has 1-1.5% Mitragynine. Indeed, even very strong Kratom can have just 1% Mitragynine, meaning there is 10 milligrams of Mitragynine per gram.
On the other hand, 7-hydroxymitragynine is found in concentrations of 0.01% to 0.05% in Kratom, and typically potent Kratom has only 0.02-0.03% 7-hydroxymitragynine, which is 0.2-0.3 mg of 7-hydroxymitragynine per gram.
Based on the percentage alone, it would seem 7-hydroxymitragynine has no effect compared to Mitragynine, since there is very little of it in natural Kratom. However, 7-hydroxymitragynine is much more potent than Mitragynine, and ultimately is responsible for most of Kratom’s effects as will be discussed below.
A scientific study titled ‘Orally Active Opioid Compounds from a Non-Poppy Source‘ did in-depth research and found out the exact opioid potencies of the primary Kratom alkaloids. Essentially, experiments have been conducted to figure out just how potent each alkaloid is in terms of opioid effects relative to Morphine, which is the prototypical opiate. A table of the opioid potencies of Kratom alkaloids can be seen below.
The numbers on the far right of the table are the opioid potency of Kratom alkaloids relative to Morphine in terms of percentage. For example, Mitragynine is 26% as potent as Morphine, meaning Mitragynine has an opioid potency about 1/4th that of Morphine.
However, 7-hydroxymitragynine has an opioid potency of 1,071%, meaning it is 10.7X more potent than Morphine. Further, 7-hydroxymitragynine is 41X more potent than Mitragynine.
Therefore, although 7-hydroxymitragynine is present in concentrations of 0.01-0.05% in natural Kratom leaf, this is equivalent to 0.4-2% of Mitragynine in terms of opioid potency. Specifically, strong Kratom leaf typically has 0.04% of 7-hydroxymitragynine, which is equivalent to 1.6% Mitragynine.
Putting all of this together, although Kratom typically has 1-1.5% Mitragynine and 0.01-0.05% 7-hydroxymitragynine, this small amount of 7-hydroxymitragynine is actually responsible for most of Kratom’s opioid effects.
On a final note, although this study compares the potency of Kratom alkaloids to Morphine, there is an important difference. These numbers are correct for the opioid pain killing potency of Kratom’s alkaloids, but simultaneously, Kratom’s alkaloids do not cause respiratory depression nor serious physical addiction due to a lack of beta-arrestin-2 recruitment. Basically, it is useful to compare the opioid analgesic properties of Kratom’s alkaloids and Morphine, but beyond that, there is no comparison since Kratom is completely safe while opiates are dangerous.