Good question, I have mixed first generation antihistamines for many years. Doxylamine, diphenhydramine, promethazine
and / or propiomazine. Have asked dr:s, no they do not recommend it. But no-one has motivated, explained why. I am
in the dark here.. dangerous not dangerous. I do not prefer to waste my benzo-tolerance
sleeping it up. Anthistamine-combos feel more broadspecrum, more effective for sleep than just
increased dose of a single drug. Placebo or not, I really do not know.
Hope someone else got the answer