1st gen antihistamines are typically the best for opioid induced nausea
Hydroxyzine has no anticholinergic effects, and is pretty good medication in general; it and promethazine are both great for nausea, and can eliminate the pesky opioid induced nausea. Otherwise, diphenhydramine is shockingly effective-and they all potentiate, to an extent(unless it's a prodrug) an alternative without drowsiness is cetirizine, not as effective personally, although it can be used and may work just fine(take 15-20mg though) As to peppermint, not sure it will help, however there is no weird side effects I know of