• They are considered safe in pregnancy. This is not always true, since during the pregnancy, the mother's body is helping the baby's get rid of drug. Thus it is theoretically possible that worrisome accumulation of the drug might occur during breastfeeding when it wouldn't during pregnancy (though this is probably rare).
However, if the concern is for the baby's getting exposed to a drug, say an antidepressant, then the baby is getting exposed to much more drug at a much more sensitive time during pregnancy than during breastfeeding. Recent studies about withdrawal symptoms in newborn babies exposed to SSRI type antidepressants (Paxil, for example) during the pregnancy somehow managed to implicate breastfeeding as if this type of problem requires a mother not to breastfeed. (Good example of how breastfeeding is blamed for everything.) In fact, you cannot prevent these withdrawal symptoms in the baby by breastfeeding, because the baby gets so little in the milk.
• They are not absorbed from the stomach or intestines. These include many, but not all, drugs given by injection. Examples are gentamicin (and other drugs in this family of antibiotics), heparin, interferon, local anesthetics, omeprazole. Omeprazole (Losec, Prilosec) is interesting because it is destroyed very quickly in the stomach. During the manufacture of the drug, a protective layer is added to the drug to prevent its destruction and the drug is thus absorbed into the mother's body. Thus, the drug is covered by a protective layer that prevents its destruction in the stomach. However, when the baby gets the drug (in tiny amounts incidentally) there is no protective layer on the drug, so it is immediately destroyed in the baby’s stomach.
Acetaminophen (Tylenol, Tempra), alcohol (in reasonable amounts), aspirin (in usual doses, for short periods). Most antiepileptic medications, most antihypertensive medications, tetracycline, codeine, nonsteroidal antiinflammatory medications (such as ibuprofen), prednisone, thyroxin, propylthiourocil (PTU), warfarin, tricyclic antidepressants, sertraline (Zoloft), paroxetine (Paxil), other antidepressants, metronidazole (Flagyl), omperazole (Losec), Nix, Kwellada.
Note: Though generally safe, fluoxetine (Prozac) has a very long half life (stays in the body for a long time). Thus, a baby born to a mother on this drug during the pregnancy, will have large amounts in his body, and even the small amount added during breastfeeding may result in significant accumulation and side effects. These are rare, but have happened. There are two options that you might consider:
1. Stop the fluoxetine (Prozac) for the last 4 to 8 weeks of your pregnancy. In this way, you will eliminate the drug from your body and so will the baby. Once the baby is born, he will be free of drug and the small amounts in the milk will not usually cause problems and you can restart the fluoxetine (Prozac).
2. If it is not possible to stop fluoxetine (Prozac) during your pregnancy, consider changing to another drug that does not get into the milk in significant amounts once the baby is born. Two good choices are sertraline (Zoloft) and paroxetine (Paxil).
• Medications applied to the skin, inhaled (for example, drugs for asthma) or applied to the eyes or nose, are almost always safe for breastfeeding.
Drugs for local or regional anesthesia are not absorbed from the baby's stomach and are safe. Drugs for general anaesthesia will get into the milk in only tiny amounts (like all drugs) and are extremely unlikely to cause any effects on your baby. They usually have very short half lives and are eliminated extremely rapidly from your body. You can breastfeed as soon as you are awake and up to it.