To the Editor: We appreciate Dr. Carlson’s comments on the main findings from our Lithium Moderate-Dose Use Study (LiTMUS) (1). LiTMUS included treatment-seeking patients who had at least some distress from symptoms in the context of a bipolar I or II diagnosis. Thus, in contrast to the participants included in the Gelenberg et al. study (2), this comparative effectiveness study included the types of patients who would be seen in clinical practice—and therefore the results of the study would be generalizable enough to inform clinicians. Additionally, the question addressed in LiTMUS was not whether or not lithium works, as implied by Dr. Carlson, but whether moderate doses of lithium would minimize side effects and add therapeutic benefit as a part of guideline-informed, evidence-based psychopharmacological treatment. We found that low levels of lithium did not have additive effects apart from a modest decrease in the use of second-generation antipsychotics. The study does not “disprove lithium’s efficacy,” but instead provides evidence that blood levels around 0.4 mEq/L may be insufficient to improve 6-month outcomes for this outpatient sample above and beyond what can be achieved with other medications. Nolen and Weisler (3) recently confirmed the lack of effectiveness for low levels of lithium for maintenance treatment.