Medical marijuana is legal where we live; is it effective at combating insomnia?

I have friends who have tried nearly everything imaginable for their chronic insomnia, but still cannot stay asleep for more than a few hours. They’ve already tried Ambien, Lunesta, Sonata, Seroquel, the four popular benzodiazepines, melatonin, diphenhydramine, and other drugs, but nothing works, not even exercise, and sleep apnea has been ruled out.