People said they slept better; the electrodes showed no change
In 184 adults with mild insomnia, 50 mg at bedtime raised self-reported sleep efficiency over two weeks. The same nights' recordings found no difference on any sleep measure.
What the study found
The benefit showed in sleep diaries and not in the recordings
In 184 adults with mild insomnia, 50 mg of diphenhydramine at bedtime raised self-reported sleep efficiency more than placebo over two weeks. The same nights' electrode recordings found no group difference on any sleep-continuity measure, with deep and dreaming sleep unchanged.
The caveat · Sized for diaries, not recordings
The trial was powered on the diary outcome, so a flat recording is a difference not detected rather than a difference shown to be absent. Mild insomnia in adults averaging 44, not the older people the warnings are about. The drug arm ran 14 nights, so nothing here reaches beyond a fortnight.