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The serotonin hypothesis of depression is still influential. We aimed to synthesise and evaluate evidence on whether depression is associated with lowered serotonin concentration or activity in a systematic umbrella review of the principal relevant areas of research. PubMed, EMBASE and PsycINFO were searched using terms appropriate to each area of research, from their inception until December 2020. Systematic reviews, meta-analyses and large data-set analyses in the following areas were identified: serotonin and serotonin metabolite, 5-HIAA, concentrations in body fluids; serotonin 5-HT 1A receptor binding; serotonin transporter (SERT) levels measured by imaging or at post-mortem; tryptophan depletion studies; SERT gene associations and SERT gene-environment interactions. Studies of depression associated with physical conditions and specific subtypes of depression (e.g. bipolar depression) were excluded. Two independent reviewers extracted the data and assessed the quality of included studies using the AMSTAR-2, an adapted AMSTAR-2, or the STREGA for a large genetic study. The certainty of study results was assessed using a modified version of the GRADE. We did not synthesise results of individual meta-analyses because they included overlapping studies. The review was registered with PROSPERO (CRD42020207203). 17 studies were included: 12 systematic reviews and meta-analyses, 1 collaborative meta-analysis, 1 meta-analysis of large cohort studies, 1 systematic review and narrative synthesis, 1 genetic association study and 1 umbrella review. Quality of reviews was variable with some genetic studies of high quality. Two meta-analyses of overlapping studies examining the serotonin metabolite, 5-HIAA, showed no association with depression (largest n  = 1002). One meta-analysis of cohort studies of plasma serotonin showed no relationship with depression, and evidence that lowered serotonin concentration was associated with antidepressant use ( n  = 1869). Two meta-analyses of overlapping studies examining the 5-HT 1A receptor (largest n  = 561), and three meta-analyses of overlapping studies examining SERT binding (largest n  = 1845) showed weak and inconsistent evidence of reduced binding in some areas, which would be consistent with increased synaptic availability of serotonin in people with depression, if this was the original, causal abnormaly. However, effects of prior antidepressant use were not reliably excluded. One meta-analysis of tryptophan depletion studies found no effect in most healthy volunteers ( n  = 566), but weak evidence of an effect in those with a family history of depression ( n  = 75). Another systematic review ( n  = 342) and a sample of ten subsequent studies ( n  = 407) found no effect in volunteers. No systematic review of tryptophan depletion studies has been performed since 2007. The two largest and highest quality studies of the SERT gene, one genetic association study ( n  = 115,257) and one collaborative meta-analysis ( n  = 43,165), revealed no evidence of an association with depression, or of an interaction between genotype, stress and depression. The main areas of serotonin research provide no consistent evidence of there being an association between serotonin and depression, and no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations. Some evidence was consistent with the possibility that long-term antidepressant use reduces serotonin concentration.

The efficacy of antidepressants in the acute treatment of moderate-to-severe depression remains a controversial issue. The minimal important difference (MID) is relevant to judge the clinical significance of treatment effects. In this analysis paper, we discuss estimates of the MID for common depression outcome measures.For the Hamilton Depression Rating Scale 17-item Version (HDRS-17), according to both anchor-based and distribution-based approaches, MID estimates range from 3 to 8 points, and the most accurate values are likely between 3 and 5 points. For the 6-item version (HDRS-6), MID estimates range between 2 and 4 points. For both the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Beck Depression Inventory II (BDI-II), MID estimates range between 3 and 9 points, with estimates of 3–6 points likely being the most accurate. Quality of life appears to be more important to patients than core depression symptoms. We thus also evaluated the Short-Form 36 (SF-36) mental component score, a popular mental-health-related quality of life measure. Its MID estimate is likely about 5 points. By contrast, the average treatment effects of antidepressants on the HDRS-17, HDRS-6, MADRS, BDI-II and SF-36 are 2 points, 1.5 points, 3 points, 2 points and 3–5 points, respectively.In conclusion, the efficacy of antidepressants in the acute treatment of moderate-to-severe depression consistently fails to exceed the lower bound of the MID estimates for common depression outcome measures. The clinical significance of antidepressants thus remains uncertain and we call for more research on quality of life measures, which are the patients’ most valued outcome domains.

The aim of this article is to discuss the validity of relapse prevention trials and the issue of withdrawal confounding in these trials. Recommendations for long-term antidepressant treatment are based almost exclusively on discontinuation trials. In these relapse prevention trials, participants with remitted depression are randomised either to have the antidepressant abruptly discontinued and replaced by inert placebo or to continue active treatment. The drug–placebo difference in relapse rates at the end of the maintenance phase is then interpreted as a prophylactic drug effect. These trials consistently produce remarkable benefits for maintenance treatment. However, the internal validity of this trial protocol is compromised, as research has shown that abruptly stopping antidepressants can cause severe withdrawal reactions that lead to (or manifest as) depression relapses. That is, there is substantial withdrawal confounding in discontinuation trials, which renders their findings uninterpretable. It is not clear to what degree the drug–placebo separation in relapse prevention (discontinuation) trials is due to withdrawal reactions, but various estimations suggest that it is presumably the majority. A review of findings based on other methodologies, including real-world long-term effectiveness trials like STAR*D and various naturalistic cohort studies, do not indicate that antidepressants have considerable prophylactic effects. As absence of evidence does not imply evidence of absence, no definitive conclusions can be drawn from the literature. To enable a thorough risk–benefit evaluation, real-world effectiveness trials should not only focus on relapse prevention, but also assess antidepressants’ long-term effects on social functioning and quality of life. Thus far, reliable long-term data on these outcome domains are lacking.

It has been claimed that efficacy estimates based on the Hamilton Depression Rating-Scale (HDRS) underestimate antidepressants true treatment effects due to the instrument's poor psychometric properties. The aim of this study is to compare efficacy estimates based on the HDRS with the gold standard procedure, the Montgomery-Asberg Depression Rating-Scale (MADRS). We conducted a meta-analysis based on the comprehensive dataset of acute antidepressant trials provided by Cipriani et al. We included all placebo-controlled trials that reported continuous outcomes based on either the HDRS 17-item version or the MADRS. We computed standardised mean difference effect size estimates and raw score drug-placebo differences to evaluate thresholds for clinician-rated minimal improvements (clinical significance). We selected 109 trials (n = 32,399) that assessed the HDRS-17 and 28 trials (n = 11,705) that assessed the MADRS. The summary estimate (effect size) for the HDRS-17 was 0.27 (0.23 to 0.30) compared to 0.30 (0.22 to 0.38) for the MADRS. The effect size difference between HDRS-17 and MADRS was thus only 0.03 and not statistically significant according to both subgroup analysis (p = 0.47) and meta-regression (p = 0.44). Drug-placebo raw score difference was 2.07 (1.76 to 2.37) points on the HDRS-17 (threshold for minimal improvement: 7 points according to clinician-rating and 4 points according to patient-rating) and 2.99 (2.24 to 3.74) points on the MADRS (threshold for minimal improvement: 8 points according to clinician-rating and 5 points according to patient-rating). Overall there was no meaningful difference between the HDRS-17 and the MADRS. These findings suggest that previous meta-analyses that were mostly based on the HDRS did not underestimate the drugs' true treatment effect as assessed with MADRS, the preferred outcome rating scale. Moreover, the drug-placebo differences in raw scores suggest that treatment effects are indeed marginally small and with questionable importance for the average patient.

The literature on persistent antidepressant withdrawal symptoms is sparse. This systematic review is the first to examine the prevalence, duration, severity, risk/protective factors and treatment strategies for post-acute withdrawal syndrome (PAWS) following the discontinuation of antidepressant medications. We searched PubMed, Web of Science and PsycInfo, focusing on newer-generation antidepressants. The electronic database search was complemented with handsearching reference lists of pivotal studies. We included original studies in adults reporting on PAWS and providing data about epidemiology and clinical management of withdrawal symptoms persisting for at least 6 weeks. The literature search yielded 1286 results, with 26 records assessed for eligibility, and seven studies fulfilled our selection criteria. Prevalence data were sparse, with one small cohort study reporting a 15% prevalence rate for PAWS in patients with panic disorder and agoraphobia. The duration of PAWS varied considerably across studies, ranging from 1.5 to 166 months. Long-term paroxetine use emerged as a potential risk factor for the development of PAWS. There was no reliable evidence to support the effectiveness of various treatment strategies, including the reinstatement of antidepressant medication, the use of benzodiazepines and the provision of cognitive-behavioral therapy. The current evidence on PAWS is sparse and predominantly of low certainty. The presence of withdrawal symptoms, lasting several months and possibly even years in some patients, underscores the need for further research with rigorous methodology. Large prospective cohort studies are needed to assess the epidemiology of PAWS, while randomized controlled trials are quired to test the efficacy of clinical interventions to treat PAWS. CRD42023461793.

BackgroundThere is ongoing controversy whether antidepressant use alters suicide risk in adults with depression and other treatment indications.MethodsSystematic review of observational studies, searching MEDLINE, PsycINFO, Web of Science, PsycARTICLES and SCOPUS for case–control and cohort studies. We included studies on depression and various indications unspecified (including off-label use) reporting risk of suicide and/or suicide attempt for adult patients using selective serotonin reuptake inhibitors (SSRI) and other new-generation antidepressants relative to non-users. Effects were meta-analytically aggregated with random-effects models, reporting relative risk (RR) estimates with 95% CIs. Publication bias was assessed via funnel-plot asymmetry and trim-and-fill method. Financial conflict of interest (fCOI) was defined present when lead authors’ professorship was industry-sponsored, they received industry-payments, or when the study was industry-sponsored.ResultsWe included 27 studies, 19 on depression and 8 on various indications unspecified (n=1.45 million subjects). SSRI were not definitely related to suicide risk (suicide and suicide attempt combined) in depression (RR=1.03, 0.70–1.51) and all indications (RR=1.19, 0.88–1.60). Any new-generation antidepressant was associated with higher suicide risk in depression (RR=1.29, 1.06–1.57) and all indications (RR=1.45, 1.23–1.70). Studies with fCOI reported significantly lower risk estimates than studies without fCOI. Funnel-plots were asymmetrical and imputation of missing studies with trim-and-fill method produced considerably higher risk estimates.ConclusionsExposure to new-generation antidepressants is associated with higher suicide risk in adult routine-care patients with depression and other treatment indications. Publication bias and fCOI likely contribute to systematic underestimation of risk in the published literature.RegistrationOpen Science Framework, https://osf.io/eaqwn/

Background The issue of unblinded outcome-assessors and patients has repeatedly been stressed as a flaw in allegedly double-blind antidepressant trials. Unblinding bias can for example result from a drug‘s marked side effects. If such unblinding bias is present for a given drug, then it might be expected that the placebos of that drug are rated significantly less effective than that of other antidepressants. Methods To test this hypothesis, the present exploratory analysis conducted a Bayesian network meta-analysis (NMA) comparing the efficacy of 19 different placebos in placebo-controlled trials provided in the dataset by Cipriani et al. (Lancet 2018; 391: 1357–66). Primary outcome was efficacy (continuous) estimated on the standardized mean difference (SMD) scale and defined as the pre-post change on the Hamilton Depression scale (HAMD-17), on which information was available in N  = 258 trials. Results Comparative placebo ranking suggested mirtazapine-placebo (SMD -2.0 [− 5.0–1.0 95% CrI]) to be the most, and amitriptyline- (SMD 1.2 [− 1.6–3.9 95% CrI]) and trazodone- (SMD 2.1 [− 0.9–5.2 95% CrI]) placebos to be the least effective placebos. Other placebos suggested to be more effective than amitriptyline- and trazodone-placebos (based on 95% CrIs excluding zero) were citalopram, desvenlafaxine, duloxetine, escitalopram, fluoxetine, sertraline, and venlafaxine placebos. These NMA results were corroborated by the observation that the relative efficacy between drug and placebo was considerably larger for amitriptyline and trazodone than for instance mirtazapine, duloxetine, and venlafaxine, supported by a small and insignificant correlation between drug-efficacy and placebo-efficacy (r = − 0.202, p  = 0.408). Discussion The present exploratory NMA indicates that distinguishable side effects of older drugs may unblind outcome-assessors thus resulting in overestimation of the average drug-placebo difference and underrating bias in placebo-arms, particularly for the older antidepressant drugs amitriptyline and trazodone. If confirmed in prospective studies, these findings suggest that efficacy rankings for antidepressants are susceptible to bias and should be considered unreliable or misleading. The analysis is limited by the focus on the single-comparison placebos (76%, i.e., placebos assessed in two-arm trials), since double-comparison placebos (25%, i.e., placebos assessed in three-arm trials) are hard to interpret and therefore not included in the present interpretation. Another limitation is the problem of multiplicity, which was only approximately accounted for in the Bayesian NMA by modelling treatment effects as exchangeable.