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Identifying Teratogens

What studies are conducted to determine whether an agent is a teratogen?

The following studies may be conducted to determine whether or not an agent is a teratogen:

How are medications rated for their safety?

Prior to 1980, most medications included literature that stated that their use in pregnancy had not been approved. The US Food and Drug Administration (FDA) has since created five drug categories, to designate the safety of medications for their use during pregnancy, including the following. Always consult your physician before taking any medication during pregnancy.




Medication has not shown an increased risk for birth defects in human studies.


Animal studies have not demonstrated a risk and there are no adequate studies in humans, OR animal studies have shown a risk, but the risk has not been seen in humans.


Animal studies have shown adverse effects, but no studies are available in humans, OR studies in humans and animals are not available.


Medications that are associated with birth defects in humans, however, there may be potential benefits in rare cases that outweigh their known risks.


Medications are contraindicated (should not be used) in human pregnancy, because of known fetal abnormalities that have been demonstrated in both human and animal studies.

There have been thousands of medications studied over the years, and only about 30 to 40 have been found to have teratogenic effects in humans. It is always important, however, for a woman who thinks she could be pregnant, or is pregnant, to ask her physician about the safety of a medication or over-the-counter medication, vitamin, mineral, or herbal supplement before taking it.

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