Multiple news media and even medical professionals have repeated the claim that 7-hydroxymitragynine (7-OH) is “13 times stronger than morphine” as though it is a fact established through rigorous science. Where does this claim come from and how accurate is it?
The claim comes from studies from 2002 (Takayama, et al) and 2004 (Matsumoto, et al) in which guinea pig ileum (a segment of the small intestine) is tested with electrical stimulation. Guinea pig ileum is used in pharmacological experimentation for opioids because it is rich in mu- and kappa-opioid receptors. The inhibition of smooth muscle contraction as a response to pain (in this case, an electrical shock) also occurs in humans as an effect of opioids. In the Takayama and Matsumoto studies, researchers observed that muscle contractions were 13 times more inhibited in the guinea pig ileum that had been administered 7-OH than in the ileum that had been administered morphine.
However, scientists never assume that animal or animal-tissue models directly translate to effects in living humans. In fact, different tests have produced very different results. In a 2016 study (Kruegel, et al), while 7-OH showed a consistent agonism at mu-opioid receptors (MOR), mitragynine showed agonism or antagonism at MOR depending on the species (mouse or rat). The researchers therefore concluded that “this interspecies variation may present significant challenges in the development of compounds in this class as novel therapeutics, as activity in rodent models may not be easily translatable to humans.”
In another Matsumoto study in 2006, living mice were given 7-OH and morphine subcutaneously (directly under the skin). This time, 7-OH “produced antinociceptive effects about 5.7 and 4.4 times more potent than those of morphine in the tail-flick (ED50=0.80 mg/kg) and hot-plate (ED50=0.93 mg/kg) tests, respectively.”
In a recent study measuring respiratory depression in rats (Zuarath Gonzales et al, 2025) “The potency of 7-HMG to decrease minute volume by 50% was 4.5-fold greater than that of morphine.”
Yet a 2020 study in rats (Behnoon-Rod, et al) concluded “These initial findings indicate that mitragynine and 7-hydroxymitragynine are not rewarding in the ICSS procedure. The present results suggest that these kratom alkaloids do not have abuse potential.” From Wikipedia, “Intracranial self-stimulation (ICSS) is an operant conditioning procedure used to study brain stimulation reward (BSR). Subjects with permanently implanted electrodes in specific brain regions are trained to perform actions, such as lever pressing, to receive direct electrical stimulation, which serves as a reward. This method is crucial for studying addiction, rewarding behaviors, and the impact of pharmacological manipulations on reward sensitivity. “
It is also worth mentioning that other studies have shown 7-OH to be a partial opioid agonist that does not signal at the beta-arrestin pathway, the pathway thought to cause respiratory depression. This contradicts animal and animal tissue models showing that 7-OH does cause respiratory depression and that it is reversed by naloxone.
Media reports and claims from various prohibitionists (even medical professionals and health departments) are clearly going with the strongest numbers available from animal tissue studies that are over 20 years old, despite various studies showing 7-OH to be less than half as strong as the “13 times” claim, similar to morphine, or not even as strong as morphine. Strength is also a relative term that could mean MOR binding affinity, smooth muscle or pain response, reward behavior in lab animals, and perhaps most importantly in the experience reported by humans taking 7-OH for various reasons. The most truthful thing that can be said about 7-OH in relation to its strength is that more research is necessary before making definitive statements.
Partial List of “7-OH is 13 times stronger than morphine” Claims in News Media
- Covered by Kratom Science, a Mississippi Sheriff declares kratom, not 7-OH, to be 13 times stronger than morphine…https://www.kratomscience.com/2019/08/01/a-mississippi-task-force-is-spreading-propaganda-across-the-state-to-ban-kratom/
- “‘13 times stronger than morphine’: Missouri DHSS issues health advisory over synthetic kratom.”
https://www.kctv5.com/2025/11/03/13-times-stronger-than-morphine-missouri-dhss-issues-health-advisory-over-synthetic-kratom/ - “The compound can be up to 13 times stronger than morphine at opioid receptors.”
https://www.kctv5.com/2025/11/03/13-times-stronger-than-morphine-missouri-dhss-issues-health-advisory-over-synthetic-kratom/ - “Health leaders say 7-OH has a potent psychoactive compound, up to 13 times stronger than morphine at opioid receptors.”
https://www.kfvs12.com/2025/11/03/health-leaders-issue-advisory-7-oh-missouri/ - “While kratom itself is a natural botanical, isolated 7-OH is far more potent—up to 13 times stronger than morphine at opioid receptors.”
https://www.yahoo.com/news/articles/kratom-derived-opioid-substance-poses-202101305.html - “Isolated 7-OH is up to 13 times stronger than morphine.”
https://www.kfmo.com/news/missouri-news/state-health-officials-warn-of-dangerous-kratom-derivative-found-in-missouri-products - “Isolated 7-hydroxymitragynine is significantly more powerful—up to 13 times stronger than morphine at opioid receptors.”
https://www.kttn.com/missouri-issues-advisory-on-7-oh-after-surge-in-emergency-calls/ - “Myth: Isolated 7-OH is far more potent — up to 13 times stronger than morphine at opioid receptors.”
https://www.eznewswire.com/newsroom/hart-responds-misleading-reports-7-oh-kratom - “Isolated 7-OH is far more potent — up to 13 times stronger than morphine at opioid receptors.”
https://www.monroe-ralls.com/articles/4897/view/missouri-dhss-issues-health-advisory-on-7-oh-potent-opioid-like-substance-poses-public-health-risk7-oh-product - “Two weeks later, Uthmeier derided the compound as 13 times stronger than morphine.”
https://www.yahoo.com/news/articles/gas-station-morphine-florida-issue-154831629.html - “Dr. Heidi Miller… says it can be up to 13 times stronger than morphine.”
https://www.missourinet.com/2025/11/04/missouri-warns-public-about-7-oh-products/ - “7-OH is 13 times stronger than morphine at affecting the body’s opioid receptors.”
https://health.mo.gov/safety/foodsafety/kratom/index.php - “Isolated 7-OH is far more potent—up to 13 times stronger than morphine at opioid receptors.”
https://www.thesalemnewsonline.com/news/article_295c486f-6e57-5a83-8851-ade43ccde15b.html - “7-hydroxymitragynine is up to 13 times stronger than morphine.”
https://www.nutraingredients.com/Article/2025/12/04/fda-seizes-1-million-in-7-oh-products/ - “7-OH is reportedly 13 times more potent than morphine.”
https://www.verywellhealth.com/7-oh-kratom-byproducts-11788990 - “7-OH… a powerful opioid compound found in kratom that is 13 times stronger than morphine.”
https://nypost.com/2025/08/06/us-news/rfk-jr-launches-crackdown-on-kratom-legal-morphine-substance-often-found-in-smoke-shop-products/ - “Indeed 7-OH (7-hydroxymitragynine)… is 13 times stronger than morphine.”
https://www.thetimes.co.uk/article/kratom-dangers-experience-drug-wt2ggfzjs - “The substance can be up to 13 times stronger than morphine.”
https://www.kshb.com/news/local-news/missouri-health-officials-issue-advisory-after-increase-in-7-oh-exposures - “7-hydroxymitragynine may be up to 13 times stronger than morphine.”
https://www.wibw.com/2025/11/03/missouri-health-officials-warn-about-7-oh-products/ - “7-OH is far more potent — up to 13 times stronger than morphine at opioid receptors.”
https://www.ksdk.com/article/news/health/missouri-health-advisory-7-oh/63-kratom-warning - “7-OH is up to 13 times stronger than morphine at opioid receptors.”
https://www.kansascity.com/news/state/missouri/article281000123.html - “The compound can be up to 13 times stronger than morphine.”
https://www.stltoday.com/news/state-regional/missouri-warning-7-oh-kratom-products/article_7f4f5b3e.html - “7-OH is reportedly 13 times stronger than morphine.”
https://www.wfla.com/news/florida/florida-bans-7-oh-kratom-compound/ - “7-OH… up to 13 times stronger than morphine at opioid receptors.”
https://www.kmov.com/2025/11/03/missouri-issues-health-advisory-7-oh/ - “The kratom derivative 7-OH can be up to 13 times stronger than morphine.”
https://www.news-leader.com/story/news/health/2025/11/03/missouri-warns-about-7-oh-products/
Scientific References
- Behnood-Rod, A., Chellian, R., Wilson, R., Hiranita, T., Sharma, A., Leon, F., McCurdy, C. R., McMahon, L. R., & Bruijnzeel, A. W. (2020). Evaluation of the rewarding effects of mitragynine and 7-hydroxymitragynine in an intracranial self-stimulation procedure in male and female rats. Drug and alcohol dependence, 215, 108235. https://doi.org/10.1016/j.drugalcdep.2020.108235
- Kruegel, A. C., Gassaway, M. M., Kapoor, A., Váradi, A., Majumdar, S., Filizola, M., Javitch, J. A., & Sames, D. (2016). Synthetic and Receptor Signaling Explorations of the Mitragyna Alkaloids: Mitragynine as an Atypical Molecular Framework for Opioid Receptor Modulators. Journal of the American Chemical Society, 138(21), 6754–6764. https://doi.org/10.1021/jacs.6b00360
- Matsumoto, K., Hatori, Y., Murayama, T., Tashima, K., Wongseripipatana, S., Misawa, K., Kitajima, M., Takayama, H., & Horie, S. (2006). Involvement of mu-opioid receptors in antinociception and inhibition of gastrointestinal transit induced by 7-hydroxymitragynine, isolated from Thai herbal medicine Mitragyna speciosa. European journal of pharmacology, 549(1-3), 63–70. https://doi.org/10.1016/j.ejphar.2006.08.013
- Matsumoto, K., Horie, S., Ishikawa, H., Takayama, H., Aimi, N., Ponglux, D., & Watanabe, K. (2004). Antinociceptive effect of 7-hydroxymitragynine in mice: Discovery of an orally active opioid analgesic from the Thai medicinal herb Mitragyna speciosa. Life sciences, 74(17), 2143–2155. https://doi.org/10.1016/j.lfs.2003.09.054
- Takayama, H., Ishikawa, H., Kurihara, M., Kitajima, M., Aimi, N., Ponglux, D., Koyama, F., Matsumoto, K., Moriyama, T., Yamamoto, L. T., Watanabe, K., Murayama, T., & Horie, S. (2002). Studies on the synthesis and opioid agonistic activities of mitragynine-related indole alkaloids: discovery of opioid agonists structurally different from other opioid ligands. Journal of medicinal chemistry, 45(9), 1949–1956. https://doi.org/10.1021/jm010576e
- Zuarth Gonzalez, J. D., Ragsdale, A. K., Mukhopadhyay, S., McCurdy, C. R., McMahon, L. R., Obeng, S., & Wilkerson, J. L. (2025). Mitragynine and 7-hydroxymitragynine: Bidirectional effects on breathing in rats. The Journal of pharmacology and experimental therapeutics, 392(11), 103720. https://doi.org/10.1016/j.jpet.2025.103720