Kratom pharmacology: Clues from planarians exposed to mitragynine

Physiol Behav. 2021 Oct 1:239:113499. doi: 10.1016/j.physbeh.2021.113499. Epub 2021 Jun 17.


Mitragynine (MG), the most prevalent bioactive alkaloid in kratom, displays nanomolar affinity for µ, κ and δ opioid receptors and produces opioid-dependent antinociception and dependence in rats. Here, using a battery of behavioral assays, we investigated MG effects in planarians. Acute MG exposure (< 100 μM) did not affect planarian motility or environmental preference, but reduced motility was detected during abstinence from chronic MG (1, 10 μM). MG (10 μM) produced place conditioning effects that were reduced by naltrexone (10 μΜ). These results suggest that MG produces opioid-sensitive reinforcing effects in planarians and MG pharmacology is conserved across different species.

Keywords: Dependence; Invertebrate; Kratom; Mitragynine; Opioid; Place preference; Planarian.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Mitragyna*
  • Naltrexone / pharmacology
  • Planarians*
  • Rats
  • Secologanin Tryptamine Alkaloids* / pharmacology


  • Secologanin Tryptamine Alkaloids
  • Naltrexone
  • mitragynine