Hydroxyzine - antagonist at the following receptors: α1-adrenergic (Ki = ~300 n M) H1 (Ki = 2 n M) 5-HT2A (Ki = ~50 n M) D2 (Ki = 378 n M) m ACh (Ki = 10,000 n M) Promethazine - antagonist at the following receptors: (*I'll try to find exact numbers) α1-adrenergic (weak to moderate) D2 (weak to moderate) H1 (strong) 5-HT2A (weak to moderate) 5-HT2C (weak to moderate) m ACh (moderate) Doxylamine - I can't find the info on right now, I'll try to find it and add it. Or a couple with different mechanisms to alternate in order to reduce possibility of dependence.
Generally the broader action that these compounds have at blocking receptors, the more sedatibg they will be.
I know this thread is a little old, but I thought I'd chime in anyways.
Even seroquel at tolerance-level dosing gave me very uncomfortable nightmarish RLS/insomnial hellacious torture that I would never wish to endure ever again.
My only interest here is to know what works acutely and is not going to pussyfoot around.
You can't compare all of these because they all have very different effects around the body.
Sure, they may all antagonize H1, but antagonization of H1 is not the only thing that produces sedation!
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I can't tell if the sedative properties of certain antihistamines results from their H1 antagonism or if it's because of their cross effect with antagonizing the adrenergic receptors.
Adrenergic antagonism helps with sedation/anxiolysis too. A few antihistamines can have additional mechanisms of action that may add to anxiolysis/relaxation/sedation.