Many mothers need to take medications while breastfeeding.  Most medications are safe while breastfeeding. 

Pain and fever:  Ibuprofen and naproxen sodium are safe for fever and pain.  Talk with your doctor (Mother's OB or FP or internist) about prescription pain medications.

Cough and Cold:  Decongestants (cold medicines) might decrease milk supply, so watch your infant for hunger cues if you take a cold medication.  Saline to your nose and keeping a vaporizer (without menthol medication) in your room safely helps your congestion.

Caffeine:  One caffeinated beverage per day is generally felt to be safe.

Alcohol is generally best to avoid.  If you do drink occasionally, eat a well balanced meal and only drink small amounts of alcohol with large amounts of water.  There is no need to pump and dump, but avoid breastfeeding for 3 hours.   Do not breastfeed if you feel drunk, as your breastmilk will have the most alcohol at this time.  Your body and breastmilk will clear out the alcohol over time, but this amount of time is related to how much is ingested and the weight of the mother.

Other medications:  You can search LactMed for medication safety.