Insomnia or difficulty falling and or staying asleep is experienced by up to 30% of the general population. This randomised crossover double-blind placebo-controlled 6-week trial aimed to assess the tolerability and effectiveness of the Entoura-10:15 medicinal cannabis oil on sleep in adults with insomnia. A total of 29 participants with self-reported clinical insomnia completed the crossover trial. Participants were randomly allocated to receive placebo or active oil containing 10 mg/ml tetrahydrocannabinol (THC) and 15 mg/ml cannabidiol (CBD) over 2-weeks titrated 0.2-1.5 ml/day, followed by a 1-week wash-out period before crossover. Tolerability was assessed by daily diary. Effectiveness was measured by saliva midnight melatonin levels, validated questionnaires, i.e., the Insomnia Severity Index, and the Fitbit activity/sleep wrist tracker. Entoura-10:15 medicinal cannabis oil was generally well tolerated, and was effective in improving sleep, whereby 60% of participants no longer classified as clinical insomniacs at the end of the 2-week intervention period. Midnight melatonin levels significantly improved in the active group by 30% compared to a 20% decline in the placebo group (p = 0.035). Medicinal cannabis oil improved both time and quality of sleep, in particular light sleep increased by 21 min/night compared to placebo (p = 0.041). The quality of sleep improved overall by up to 80% in the active group (p_Phase2 = 0.003), including higher daily functioning (p = 0.032). Observed effects were more pronounced in Phase 2 due to the period effect and loss of blinding. Entoura-10:15 medicinal cannabis oil was well tolerated and effective in improving sleep in adults with insomnia.