Here's a link to the outcome of a small scale study done on the effectiveness of medicinal cannabis for insomnia.
academic.oup.com/sleep/arti...
The study concluded that:
"Two weeks of nightly sublingual administration of a cannabinoid extract (ZTL-101) is well tolerated and improves insomnia symptoms and sleep quality in individuals with chronic insomnia symptoms."
Details of the THC/CBD/CBN ratio are in the article.
The formulation used in the study is Zenivol, a commercially available product.