Effects of Drugs during Pregnancy

Most women are exposed to drugs of one type or another during pregnancy. These may be prescribed drugs or those bought over the counter. During pregnancy, medicines can be given as a part of the management of any disorder or any medical problem.

When drugs are prescribed to a pregnant woman or a breastfeeding mother, it is very important to consider the effects of the drug not only on the woman but also on the baby. Drugs should not be used during pregnancy unless necessary.

Drugs have harmful effects on the foetus and should be avoided during pregnancy. On the other hand, some drugs are given to the woman to have a therapeutic effect on the foetus, such as betamethasone or dexamethasone are given to women at risk of preterm birth because of their effects on fetal lung maturation.

Transfer of Drugs across the Placenta and Breast

When a pregnant woman or a breastfeeding mother takes any drug which may be either prescribed or taken by herself, will be absorbed and present in the blood circulation.

Then mother’s blood will travel to the baby through the placenta or breast. The drug will pass across to the foetus in greater or lesser quantities depending on the drug type. Some drugs will not pass across into the foetus or milk at all, whereas others will pass freely depending on the size of the drug molecules.

Adverse Effects of Drug in Pregnancy

Many drugs have adverse effects during pregnancy depending on the stage of pregnancy. If drugs are taken during the first trimester when organ formation takes place in the foetus, can lead to malformations. Some of the adverse effects are listed below-

  • Miscarriage
  • Stillbirth
  • Congenital anomalies
  • Structural malformations or birth defects
  • Preterm labour
  • Intrauterine growth restriction
  • Presence of withdrawal symptoms in the baby after birth
  • Risk of sudden infant death syndrome.

During pregnancy, whatever goes into your body has an effect on the unborn baby. Be cautious before taking any drugs or consult your doctor.


The word ‘teratogen’ refers to the substance that leads to the birth of a malformed baby. Organ formation of the foetus takes place from conception to 12 weeks of pregnancy. The baby can get malformed if teratogens are taken during this time. This is an important consideration since it is a stage of pregnancy when a woman may not be aware that she is pregnant or may not have attended her doctor for advice.

If you have become pregnant and are already taking any medicine, then definitely consult a doctor.

Some of the commonly used drugs known to be teratogens are given below-


The drug thalidomide was marketed in the 1960s to treat morning sickness during pregnancy, but it was found to cause limb abnormalities and was identified as teratogens. Now it is used to treat skin conditions and cancers.


It is used as a psychiatric medication to treat depressive and bipolar disorders but its use during pregnancy has adverse effects on the unborn baby. It causes cardiac defects in the foetus.


This medication is used to treat epilepsy and nerve pain that affects your face (trigeminal neuralgia). Its use during pregnancy can lead to craniofacial anomalies.


Warfarin is an anticoagulant and is used to prevent blood clot formation in conditions such as deep vein thrombosis and pulmonary embolism. If used during pregnancy can cause facial anomalies and central nervous system anomalies in the baby.

Carbamazepine and sodium valproate

These drugs are used to control seizures and their use can lead to craniofacial anomalies and neural tube defects in the unborn baby.

Retinoic acid

Retinoic acid is made from vitamin A. It is a nutrient that the body requires in small quantities to function effectively. Its use during pregnancy has harmful effects on the growing foetus. It causes craniofacial anomalies, cardiac and central nervous system anomalies.

Drugs should be avoided in the first trimester whenever possible. Actually, this is not always possible because in some conditions such as a woman with epilepsy who is controlled with sodium valproate should not stop abruptly despite the risk of neural tube defect. Prolonged seizures during pregnancy could have dangerous effects on her and the foetus.

When a woman is on long-term medication and planning to have a pregnancy then it is advisable to attend pre-pregnancy counselling where plans can be made to minimise the risk. When a woman is exposed to a teratogen during the first trimester then the prenatal diagnosis, usually with ultrasound, should be done.


In the above post, we have discussed the effects of drugs during pregnancy. When drugs are taken during pregnancy, they cross the placenta and reach the foetus and affect their health. Where possible, drugs should be avoided in the first trimester and should consult the doctor before taking any medicine. Without the doctor’s consultation, teratogens such as lithium, warfarin, phenytoin, sodium valproate and carbamazepine, retinoic acid should be avoided during pregnancy because their use can lead to birth defects.

Thank you all!!! Hope you find this useful.

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