What drug is safe to use for Nausea during pregnancy?

Doxylamine (ex Unisom®)

Doxylamine/pyridoxine considered safe in pregnancy.

Pyridoxine, or Vitamin B6 is a water-soluble vitamin found naturally in many foods, as well as added to foods and supplements.

Doxylamine/pyridoxine combination considered first-line per SOGC guideline, Motherisk and ACOG guideline.

The SOGC is one of Canada’s oldest national specialty organizations. It's short for the Society of Obstetricians and Gynaecologists of Canada.  The ACOG is the American College of Obstetricians and Gynecologists.

Dose is 12.5 mg three or four times daily (plus pyridoxine- B6) 6mg or 12.5mg to 25 mg three times daily 

Diclectin® is the Canadian formulation of doxylamine and pyridoxine.

Just as a point of Interest- Generic Diclectin  (and many other medications) contains a very small, safe amount of mannitol that is much lower than the amount found naturally in foods.