What do systematic reviews say?

Antihistamines vs placebo

It is very uncertain whether antihistamines changes vomiting ‐ postoperative compared with placebo (very low certainty).

• Interventions for preventing nausea and vomiting in women undergoing regional anaesthesia for caesarean section 2021 · Cochrane Headline outcomes only
  RR 0.48 [0.29, 0.81]
  3 studies · 333 participants
  Very low