Background: A huge gap exists between the production of evidence and its uptake in clinical practice settings. To fill this gap, treatment guidelines, based on explicit assessments of the evidence base, are commonly used in several fields of psychiatry, including schizophrenia and related psychotic disorders. However, it remains unclear whether treatment guidelines have any material impact on provider performance and patient outcomes, and how implementation should be conducted to maximise benefit. Objectives: The primary objective of this review was to examine the efficacy of guideline implementation strategies in improving process outcomes (performance of healthcare providers) and patient outcomes. We also explored which components of different guideline implementation strategies could influence them. Search methods: We searched the Cochrane Schizophrenia Group Register (March 2012 and August 2015), as well as references of included studies. Selection criteria: Studies that examined schizophrenia-spectrum disorders to compare guideline implementation strategies with usual care or to assess the comparative efficacy of different guideline implementation strategies. Data collection and analysis: Review authors worked independently and in duplicate to critically appraise records from 990 studies; six individual studies met the inclusion criteria. Among the six included studies, significant heterogeneity was found in the focus of the guideline, target of the intervention, implementation strategy, and outcome measures, so meta-analysis was carried out for antipsychotic co-prescribing only. Main results: This review now includes six studies, with a total of 1727 participants. Of the six included studies, practitioner impact was assessed in four. Overall, risk of bias was rated as low or unclear, and all evidence in the 'Summary of findings' tables was graded as low or very low quality. Meta-analysis revealed that a combination of several guideline dissemination and implementation strategies targeting healthcare professionals did not reduce antipsychotic co-prescribing in schizophrenia outpatients (2 RCTs, N = 1082, RR 1.10 CI 0.99 to 1.23; corrected for cluster design: N = 310, RR 0.97, CI 0.75 to 1.25, very low-quality evidence). One trial, which studied a nurse-led intervention aimed at promoting cardiovascular disease screening, found a significant effect in the proportion of people receiving screening (Framingham score: N = 110, RR 0.69, 95% CI 0.55 to 0.87), although in the analysis corrected for cluster design, the effect was no longer statistically significant (N = 38, RR 0.71, 95% CI 0.48 to 1.03, very low-quality evidence). One trial reported the patient outcomes of global state, satisfaction with care, treatment adherence, and drug attitude; no effect between treatments was seen. Quality of life was not reported by any of the studies. One trial, which studied the use of re-written guideline text compared to original text, did not find a significant effect on staff receiving training (N = 68, RR 1.03, 95% CI 0.87 to 1.21, low-quality evidence), staff receiving supervision (N = 68, RR 0.86, 95% CI 0.64 to 1.17, low-quality evidence), or staff providing psychological interventions (N = 68, RR 0.86, 95% CI 0.62 to 1.18, low-quality evidence). Regarding participant outcomes, only one trial assessed the efficacy of a shared decision-making implementation strategy and found no impact on psychopathology, satisfaction with care, or drug attitude. Another single trial studied a multifaceted intervention to promote medication adherence and found no effect on adherence rates. Authors' conclusions: Considering the available evidence, it is not possible to arrive at definitive conclusions. The preliminary pattern of evidence suggests that uncertainty remains about clinically meaningful and sustainable effects of treatment guidelines on patient outcomes and how best to implement such guidelines for maximal benefit.