ObjectivesThis study aimed to assess the safety and effectiveness of self-managed misoprostol abortions obtained outside of the formal health system in Lagos State, Nigeria.DesignThis was a prospective cohort study among women using misoprostol-containing medications purchased from drug sellers. Three telephone-administered surveys were conducted over 1 month.SettingData were collected in 2018 in six local government areas in Lagos State.ParticipantsDrug sellers attempted to recruit all women who purchased misoprostol-containing medication. To remain in the study, participants had to be female and aged 18–49, and had to have purchased the medication for the purpose of abortion. Of 501 women initially recruited, 446 were eligible for the full study, and 394 completed all three surveys.Primary and secondary outcome measuresUsing self-reported measures, we assessed the quality of information provided by drug sellers; the prevalence of potential complications; and the proportion with completed abortions.ResultsAlthough drug sellers provided inadequate information about the pills, 94% of the sample reported a complete abortion without surgical intervention about 1 month after taking the medication. Assuming a conservative scenario where all individuals lost to follow-up had failed terminations, the completion rate dropped to 87%. While 86 women reported physical symptoms suggestive of complications, only six of them reported wanting or needing health facility care and four subsequently obtained care.ConclusionsDrug sellers are an important source of medical abortion in this setting. Despite the limitations of self-report, many women appear to have effectively self-administered misoprostol. Additional research is needed to expand the evidence on the safety and effectiveness of self-use of misoprostol for abortion in restrictive settings, and to inform approaches that support the health and well-being of people who use this method of abortion.