Key takeaways
Diclegis (doxylamine/pyridoxine) and Promethazine (Phenergan) are both antihistamines, but they are used for different purposes and have different mechanisms of action. Diclegis is specifically FDA-approved to treat morning sickness in pregnant women and combines doxylamine, an antihistamine, with pyridoxine, a form of vitamin B6. It is taken orally and is not suitable for severe cases of nausea and vomiting during pregnancy. Promethazine, on the other hand, is used to treat a variety of conditions including allergies, motion sickness, nausea, and vomiting, and it can be administered orally, as an injection, or as a suppository. Promethazine works by blocking histamine, dopamine, and acetylcholine, making it more versatile but also associated with a higher risk of side effects, such as constipation and potential breathing problems in children under 2 years old. While Diclegis is safe for use during the first trimester of pregnancy, Promethazine is only recommended for pregnant women if Diclegis or other first-choice options are ineffective. Both are available in generic forms.
