Yes, lettuce tea is reported to help you sleep.  This is one of the remarkable uses for the fine lettuce you receive in your weekly vegetable box or purchase at the market.

A couple of the larger outside leaves cut and steeped in hot water for 15 minutes makes the tea (you can add a bit of mint to add more flavor).

More info: http://www.thirdage.com/sleep/let-lettuce-help-you-sleep

Not so sure?  You can buy lettuce based tea: https://www.facebook.com/lettucetea