BackgroundIn England, during 2009–2014 the ‘Time to Change’ anti-stigma programme has included a social marketing campaign (SMC) using mass media channels, social media and social contact events but the efficacy of such approach has not been evaluated yet.MethodsThe target population included people aged between mid-twenties/mid-forties, from middle-income groups. Participants were recruited through an online market research panel, before and after each burst of the campaign (with a mean number of unique participants per each burst: 956.9 ± 170.2). Participants completed an online questionnaire evaluating knowledge [Mental Health Knowledge Schedule (MAKS)]; attitudes [Community Attitudes toward Mental Illness (CAMI)]; and behaviours [Reported and Intended Behaviour Scale (RIBS)]. Socio-demographic data and level of awareness of the SMC were also collected.ResultsA total of 10,526 people were interviewed. An increasing usage of the SMC-media channels as well as of the level of awareness of SMC was found (P < 0.001). Being aware of the SMC was found to be associated with higher score at MAKS (OR = 0.95, CI = 0.68 to 1.21; P < 0.001), at ‘tolerance and support’ CAMI subscale (OR = 0.12, CI = 0.09 to 0.16; P < 0.001), and at RIBS (OR = 0.71, CI = 0.51 to 0.92; P < 0.001), controlling for confounders.ConclusionThe SMC represents an important way to effectively reduce stigma. Taking into account these positive findings, further population-based campaigns using social media may represent an effective strategy to challenge stigma.