Studies indicate that cannabis (marijuana) is the most frequently used recreational substance (after tobacco and alcohol) in pregnancy despite being under-reported. The prevalence is expected to increase with the recent wave of interest in medicinal and recreational cannabis use, resulting in the reconsideration of its classification in terms of clinical and legal risks, in the backdrop of campaigns for its decriminalisation and legalisation gradually sweeping the world. This paper reviews the likely impact on the ethics of the use of cannabis in pregnancy, and implications for obstetricians, midwives, general practitioners, psychiatrists, and other clinicians managing such patients.