It has long been known that vitamin B6 has anti-emetic effects; it is often recommended for use in pregnancy to reduce morning sickness, and has been used in antiemetic drugs.
A review of therapies to manage nausea and vomiting in pregnancy noted vitamin B6 as an effective anti-nausea and antiemetic treatment. Newer research has gone on to demonstrate that it is the activated form of vitamin B6, namely, pyridoxal-5-phosphate (P5P), which is the critical compound for antiemesis.
The findings come after 283 pregnant women experiencing morning sickness were enrolled in this double- blind, randomised, multicenter, placebo-controlled study. The participants were randomised to receive either a drug containing pyridoxine hydrochloride or a placebo for 14 days, with a dosage schedule of 2-4 tablets per day.
Effectiveness of treatment was assessed via the Pregnancy-Unique Quantification of Emesis (PUQE) scoring system; blood samples were drawn on days zero, four, eight and 14 to measure plasma concentrations of doxylamine, pyridoxine, pyridoxal, and P5P.
Among the 131 women in the treatment group, PUQE scores improved steadily during the 14 days, confirming this to be an effective anti-nausea and antiemetic drug. The blood sample analysis indicated that blood levels of pyridoxine and pyridoxal remained low throughout treatment, while P5P concentrations rose in association with the antiemetic effect. This suggests that pyridoxine and pyridoxal are prodrugs for P5P, and that it is P5P which has the intended therapeutic effect.
It can be surmised from this that taking P5P directly in supplemental form may be a more efficient therapy for morning sickness than vitamin B6 in its unactivated forms.
- King TL. Evidence-based approaches to managing nausea and vomiting in early pregnancy. J Midwifery Womens Health 2009;54(6):430-444. [Abstract]
- Matok I, Clark S, Caritis S, et al. Studying the antiemetic effect of vitamin B6 for morning sickness: pyridoxine and pyridoxal are prodrugs. J Clin Pharmacol 2014;24(12):1429-1433. [Abstract]