I'm on promethazine it's an antihistamine but I'm on it for insomnia and it's definitely a drowsy one I get knocked out for a day on just one but those are on prescription however you can buy them over the counter same strength. I also have ones I take because the promethazine are a PRN that are called cetirizine dihydrochloride, they're marketed as 'non drowsy' however they do make me sleepy. So it's actually possible that some non drowsy have the reverse effects I think clarytin is really known for it.Back with the comments about meds that make you ‘drowsy’ i’m pretty sure most anti histamines these days are actually non drowsy