Table 1.

Percent Displacement of Radioligands from Human 5-HTRs by 100 nM and 10 μM Concentrations of Kratom Alkaloids^a

	binding site
kratom alkaloid	5-HT1A	5-HT1B	5-HT2A	5-HT2B	5-HT2C	5-HT3
mitragynine
100 nM	9.7	−0.2	−0.9	23.0	−8.2	−9.1
10,000 nM	76.7	8.2	49.9	90.7	14.7	−12.7
7-hydroxymitragynine
100 nM	3.1	−5.6	−0.2	−1.4	−18.3	8.2
10,000 nM	1.2	−0.8	3.9	12.4	−13.9	19.5
speciociliatine
100 nM	−4.8	3.8	1.5	−3.4	0.4	11.1
10,000 nM	33.3	16.8	68.1	47.1	14.3	0.7
speciogynine
100 nM	58.9	2.6	2.8	70.9	−18.6	11.3
10,000 nM	98.7	30.4	82.7	102.2	77.9	1.5
paynantheine
100 nM	69.4	8.9	16.8	53.8	12.7	−9.8
10,000 nM	98.7	19.5	92.8	101.5	89.3	−0.8
9-hydroxycorynantheidine
100 nM	0.2	3.0	−6.5	5.2	−10.4	−1.3
10,000 nM	29.6	−2.1	28.4	71.3	12.5	7.3
corynantheidine
100 nM	2.5	−4.2	−6.8	14.8	2.5	6.2
10,000 nM	77.3	10.7	28.7	76.3	3.8	6.8
ajmalicine
100 nM	33.2	21.6	5.1	6.2	−12.5	−2.5
10,000 nM	95.2	98.3	36.5	89.3	−5.3	1.8

^aBold fonts indicate ≥50% displacement of radioligands from the respective 5-HTR. Each experiment was conducted in duplicate. [³H]8-OH-DPAT, [¹²⁵I]CYP (+ 30 μM isoproterenol), and [³H]imipramine were used to label 5-HT_1ARs, 5-HT_1BRs, and the 5-HT transporter, respectively. [¹²⁵I](±)DOI was used to label 5-HT_2A(h), 5-HT_2B(h), and 5-HT_2C(h) receptors.