Is Zofran safe to take during pregnancy?

Zofran is safe to take during pregnancy (it's category B in the US).

Here's a great explanation of what the different Pregnancy categories mean, from the FDA (who assigns these letters) (source: depts.washington.edu/druginfo/Formulary/Pregnancy.pdf) You might need to download Adobe Reader (free online) to read this document.

"The FDA-assigned pregnancy categories as used in the Drug Formulary
are as follows:

Category A
Adequate and well-controlled studies have failed to demonstrate a risk
to the fetus in the first trimester of pregnancy (and there is no evidence
of risk in later trimesters).

Category B
Animal reproduction studies have failed to demonstrate a risk to the
fetus and there are no adequate and well-controlled studies in pregnant
women.

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Category C
Animal reproduction studies have shown an adverse effect on the fetus
and there are no adequate and well-controlled studies in humans, but
potential benefits may warrant use of the drug in pregnant women
despite potential risks.

Category D
There is positive evidence of human fetal risk based on adverse
reaction data from investigational or marketing experience or studies
in humans, but potential benefits may warrant use of the drug in
pregnant women despite potential risks.

Category X
Studies in animals or humans have demonstrated fetal abnormalities
and/or there is positive evidence of human fetal risk based on adverse
reaction data from investigational or marketing experience, and the
risks involved in use of the drug in pregnant women clearly outweigh
potential benefits."