It does not' put you to sleep,' but rather it may reduce anxiety to increase likelihood of falling asleep.

Joshua Tal

There is some evidence that 4-7-8 breathing helps reduce anxious, depressive and insomniac symptoms when comparing pre - and post-intervention, however, there are no large randomized control trials specifically on 4-7-8 breathing to my knowledge, the research on( the effect of) diaphragmatic breathing on these symptoms in general is spotty, with no clear connection due to the poor quality of the studies.

It can be a good wind-down, pre-bedtime activity.