Background: The use of amphetamines is a global public health concern. We summarise global data on use of amphetamines and mental health outcomes. Methods: A systematic review and meta-analysis (CRD 42017081893). We searched Medline, EMBASE, PsycInfo for methamphetamine or amphetamine combined with psychosis, violence, suicidality, depression or anxiety. Included studies were human empirical cross-sectional surveys, case-control studies, cohort studies and randomised controlled trials that assessed the association between methamphetamine and one of the mental health outcomes. Random effects meta-analysis was used to pool results for any use of amphetamines and amphetamine use disorders. Findings: 149 studies were eligible and 59 were included in meta-analyses. There was significant heterogeneity in effects. Evidence came mostly from cross-sectional studies. Any use of amphetamines was associated with higher odds of psychosis (odds ratio [OR] = 2.0, 95%CI 1.3–3.3), violence (OR = 2.2, 95%CI 1.2–4.1; adjusted OR [AOR] = 1.4, 95%CI 0.8–2.4), suicidality OR = 4.4, 95%CI 2.4–8.2; AOR = 1.7, 95%CI 1.0–2.9) and depression (OR = 1.6, 95%CI 1.1–2.2; AOR = 1.3, 95%CI 1.2–1.4). Having an amphetamine use disorder was associated with higher odds of psychosis (OR = 3.0, 95%CI 1.9–4.8; AOR = 2.4, 95%CI 1.6–3.5), violence (OR = 6.2, 95%CI 3.1–12.3), and suicidality (OR = 2.3, 95%CI 1.8–2.9; AOR = 1.5, 95%CI 1.3–1.8). Interpretation: Methamphetamine use is an important risk factor for poor mental health. High quality population-level studies are needed to more accurately quantify this risk. Clinical responses to methamphetamine use need to address mental health harms.