Effect: Most drugs pass through breast milk to some degree.
What to do: Follow directions for pain relievers like ibuprofen and acetaminophen, but avoid aspirin. Most OTC antihistamines/decongestants are safe but may lower milk production. If your supply decreases, drink lots of fluids and talk to your doctor about alternatives. Also, be sure to ask about the safety of any medication, including herbal supplements, you're taking.
Effect: Women who exercise strenuously may produce less milk. There may also be a slight increase in lactic acid in the milk, which can cause gas for some babies.
What to do: If you work out more than two hours daily, feed your baby beforehand and drink plenty of fluids.
Effect: Infants breastfed by vegetarian moms may be lacking in vitamin B12, since meat, poultry, and seafood are big sources.
What to do: Get at least 2.8 micrograms (mcg) of vitamin B12 daily through a multivitamin or food. If you eat eggs and dairy foods regularly, you may be fine -- a cup of skim milk has 1 mcg, and one egg has .5 mcg.
Effect: Alcohol transfers to breast milk and changes its odor and taste. Two drinks a week can decrease your supply or make your baby sleepier.
What to do: It's best not to drink. If you do, limit yourself to an occasional glass of wine or beer after nursing.
Colds and flu
Effect: By the time you feel symptoms, your baby's probably already been exposed to the virus.
What to do: Keep nursing. Cold- and flu-fighting antibodies are given to your baby through your milk, so nursing can help stave off or lessen the illness.