Well, I can see that you're getting lots of different answers. In the US (where I am, and where I know the culture around me), sleeping pills have less of a stigma than other psychiatric medications.

I would start off giving as little information as possible - just that you're not drinking alcohol because you're taking a medication that you can't drink alcohol with.

If your friends refuse to let you off with that story, then you could say that you have been having sleep problems and are taking medication for it, and that the medication stays in your bloodstream all the time, so you can't drink alcohol.

I think lots of people have seen the horror stories about people who take Ambien and drink alcohol and get amnesia and wreck a car or end up in jail for fighting. I don't think it's a common side effect, but I'd think people should understand why you wouldn't want to take the chance.

From your description of your friends, I'm assuming that they are people who find it extremely difficult to imagine having a party without alcohol. I used to have friends like that when I was much younger. Not drinking was unthinkable to them and they would insist that everyone must have drinks.

I'd choose the sleeping pill story over the antibiotics story, because I imagine you're going to need to use this story more than once.

Good luck. I have been down the road of needing to tell people that I could no longer drink alcohol because of medications. It's a little bit stressful, but by not drinking alcohol with your meds, you are doing a good thing for your health, both physical and mental.

You're also doing a good thing for your body, because generally alcohol and the kind of psych meds you're taking do not mix well at all. You'd probably feel very sick if you drank more than one drink, and even one drink might make you feel bad.

You say that a part of you wants to tell your friends the complete truth. I understand that urge to let people you know well what's going on with you.

I would just think first about how they might react - what's the worst thing that you think they might say or do? Do you think you could handle that?

Good luck with your party.