Research has suggested that frequency of use may be a key factor as to why cannabis begins to fail as a sleep aid, reports CNN.

“Most of the research has so far examined synthetically extracted cannabis compounds, mainly THC and CBD,” said Sharon Sznitman, a senior lecturer in the School of Public Health at the University of Haifa in Israel.
“This, however, cannot give us clear indication for how cannabis affects sleep in the daily lives of most cannabis users,” she said, “because most cannabis users use whole-plant based cannabis, which has more than 500 cannabinoids, and these may be interacting and creating different effects on sleep than synthetically extracted cannabinoids.”

via Weed may not ease sleep problems, especially for regular users, studies say.