Rising rates of cannabis use during pregnancy and potential negative impacts on offspring health has generated concern. A small and equivocal, but rapidly developing, literature suggests that frequent and heavy pre-natal cannabis exposure (PCE) is associated with adverse neonatal outcomes (e.g., reduced birthweight and gestational age at birth) and may be associated with child psychopathology risk (e.g., externalizing behaviour and psychosis proneness, with less evidence linking PCE to internalizing problems and cognition). Non-human animal models suggest that PCE may causally influence these outcomes; however, in humans it remains unclear whether associations are independent of confounds (e.g., genetic and environmental liability). Mixed findings may be explained on the basis of small samples, limited phenotyping, stigma, confounds, and minimal consideration of timing and frequency of exposure. In particular, given that the central endocannabinoid type 1 receptor to which cannabis constituents bind are not known to be expressed in the foetus until the second half of the first trimester, it is possible that a lack of consideration of timing of exposure may explain null associations in some studies. Collectively, data highlight concerns that PCE is associated with adverse outcomes and suggest that cannabis use during pregnancy should be discouraged while more research is conducted.