Is your stomach more likely to reject/vomit medication it's not used to?

Maybe this answer is a bit obvious (i.e. yes), but I’m looking for a few details. Like your system can tolerate more alcohol the more you drink over time, otherwise it vomits it up; does that same process also go for psych meds like for bipolar, schizo, depression, OCD, ADHD? thanks gang!!

There is no one answer. Different drugs are different. It’s more likely if nausea is a common side effect. And, very often with those types of drugs, the side effects lessen as your body gets used to them.

So if you or someone you know is having problems with those meds, it’s fairly likely it will get over time. Though you’ll need to be able to keep the medicine down for your body to get used to it.

Taking medications in certain combinations, or with or without food or even certain foods, can also result in various kinds of GI distress.

The best and most common way to prevent/decrease nausea with meds is to avoid taking them on an empty stomach.
Of course each medication is different. A very few need to be taken while you stomach is empty, some osteoporosis drugs for instance.
Some medications require you to avoid certain foods, grapefruit can cause problems with more than 40 medications.

In general however, eating a moderate amount of a bland food 15 to 20 minutes before taking a medication will eliminate or greatly decrease the feelings of nausea.