Table 1. Association of plasma serotonin concentrations with clinical outcomes.

Clinical outcomes	Remission at 4 weeks	Remission at 8 weeks	Response at 4 weeks	Response at 8 weeks	% change at 4 weeks	% change at 8 weeks
Baseline	P=0.012	P=0.028	P=0.007	P=0.047	P=0.015	P=0.019
	OR=1.41	OR=1.31	OR=1.40	OR=1.30	r=−0.14	r=−0.14
Change after 4 weeks	P=0.011	P=0.041	P=0.026	P=0.060	P=0.021	P=0.024
	OR=1.40	OR=1.27	OR=1.31	OR=1.27	r=−0.13	r=−0.13
Change after 8 weeks	P=0.069	P=0.147	P=0.037	P=0.130	P=0.041	P=0.06
	OR=1.27	OR=1.19	OR=1.29	OR=1.21	r=−0.12	r=−0.11

Abbreviation: OR, odds ratio; SSRI, selective serotonin reuptake inhibitor. Plasma serotonin concentrations at baseline and decreases in plasma serotonin concentrations after 4 weeks of SSRI treatment were nominally associated with remission, response and percent change in QIDS-C16 score. The decrease in plasma serotonin between baseline and 8 weeks of SSRI treatment was associated only with the response at 4 weeks and percent change in QIDS-C16 at 4 weeks. OR>1 indicates improvement (associated with higher baseline and larger changes in plasma serotonin concentrations) and the negative r values indicate a decrease in QIDS-C16 scores, i.e., improvement. P-values<0.05 have been bolded.