Background Lone parents in high-income countries have high rates of poverty (including in-work poverty) and poor health. Employment requirements for these parents are increasingly common. 'Welfare-to-work' (WtW) interventions involving financial sanctions and incentives, training, childcare subsidies and lifetime limits on benefit receipt have been used to support or mandate employment among lone parents. These and other interventions that affect employment and income may also affect people's health, and it is important to understand the available evidence on these effects in lone parents. Objectives To assess the effects of WtW interventions on mental and physical health in lone parents and their children living in high-income countries. The secondary objective is to assess the effects of welfare-to-work interventions on employment and income. Search methods We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE Ovid, Embase Ovid, PsycINFO EBSCO, ERIC EBSCO, SocINDEX EBSCO, CINAHL EBSCO, Econlit EBSCO, Web of Science ISI, Applied Social Sciences Index and Abstracts (ASSIA) via Proquest, International Bibliography of the Social Sciences (IBSS) via ProQuest, Social Services Abstracts via Proquest, Sociological Abstracts via Proquest, Campbell Library, NHS Economic Evaluation Database (NHS EED) (CRD York), Turning Research into Practice (TRIP), OpenGrey and Planex. We also searched bibliographies of included publications and relevant reviews, in addition tomany relevant websites. We identified many included publications by handsearching. We performed the searches in 2011, 2013 and April 2016. Selection criteria Randomised controlled trials (RCTs) of mandatory or voluntary WtW interventions for lone parents in high-income countries, reporting impacts on parental mental health, parental physical health, child mental health or child physical health. Data collection and analysis One review author extracted data using a standardised extraction form, and another checked them. Two authors independently assessed risk of bias and the quality of the evidence. We contacted study authors to obtain measures of variance and conducted meta-analyses where possible. We synthesised data at three time points: 18 to 24 months (T1), 25 to 48 months (T2) and 49 to 72 months (T3). Main results Twelve studies involving 27,482 participants met the inclusion criteria. Interventions were either mandatory or voluntary and included up to 10 discrete components in varying combinations. All but one study took place in North America. Although we searched for parental health outcomes, the vast majority of the sample in all included studies were female. Therefore, we describe adult health outcomes as 'maternal' throughout the results section. We downgraded the quality of all evidence at least one level because outcome assessors were not blinded. Follow-up ranged from 18 months to six years. The effects of welfare-to-work interventions on health were generally positive but of a magnitude unlikely to have any tangible effects. At T1 there was moderate-quality evidence of a very small negative impact on maternal mental health (standardised mean difference (SMD) 0.07, 95% Confidence Interval (CI) 0.00 to 0.14; N = 3352; studies = 2)); at T2, moderate-quality evidence of no effect (SMD 0.00, 95% CI 0.05 to 0.05; N = 7091; studies = 3); and at T3, low-quality evidence of a very small positive effect (SMD-0.07, 95% CI-0.15 to 0.00; N = 8873; studies = 4). There was evidence of very small positive effects on maternal physical health at T1 (risk ratio (RR) 0.85, 95% CI 0.54 to 1.36; N = 311; 1 study, low quality) and T2 (RR 1.06, 95% CI 0.95 to 1.18; N = 2551; 2 studies, moderate quality), and of a very small negative effect at T3 (RR 0.97, 95% CI 0.91 to 1.04; N = 1854; 1 study, low quality). At T1, there was moderate-quality evidence of a very small negative impact on child mental health (SMD 0.01, 95% CI-0.06 to 0.09; N = 2762; studies = 1); at T2, of a very small positive effect (SMD-0.04, 95% CI-0.08 to 0.01; N = 7560; studies = 5), and at T3, there was low-quality evidence of a very small positive effect (SMD-0.05, 95% CI-0.16 to 0.05; N = 3643; studies = 3). Moderate-quality evidence for effects on child physical health showed a very small negative effect at T1 (SMD-0.05, 95% CI-0.12 to 0.03; N = 2762; studies = 1), a very small positive effect at T2 (SMD 0.07, 95% CI 0.01 to 0.12; N = 7195; studies = 3), and a very small positive effect at T3 (SMD 0.01, 95% CI-0.04 to 0.06; N = 8083; studies = 5). There was some evidence of larger negative effects on health, but this was of low or very low quality. There were small positive effects on employment and income at 18 to 48 months (moderate-quality evidence), but these were largely absent at 49 to 72months (very lowtomoderate-quality evidence), often due to control groupmembersmoving intowork independently. Since the majority of the studies were conducted in North America before the year 2000, generalisabilty may be limited. However, all study sites were similar in that they were high-income countries with developed social welfare systems. Authors' conclusions The effects of WtW on health are largely of a magnitude that is unlikely to have tangible impacts. Since income and employment are hypothesised to mediate effects on health, it is possible that these negligible health impacts result from the small effects on economic outcomes. Even where employment and income were higher for the lone parents inWtW, poverty was still high for the majority of the lone parents in many of the studies. Perhaps because of this, depression also remained very high for lone parents whether they were in WtW or not. There is a lack of robust evidence on the health effects of WtW for lone parents outside North America.
