Herbs for nausea
Nausea is one of the areas where herbal evidence is strongest. Ginger in particular has been studied many times in motion sickness and pregnancy nausea.
In short
The strongest evidence for nausea is for ginger. Peppermint tea is also widely used by tradition.
The plants, strongest evidence first
Mint Mentha × piperita
Widely drunk for nausea and indigestion; peppermint leaf is accepted for traditional use in indigestion.
Ginger Zingiber officinale
The European Medicines Agency accepts ginger for nausea from motion sickness. Small studies in pregnancy nausea are positive; talk to your doctor before using it in pregnancy.