If you are breast-feeding, many substances that you eat, drink, inhale, or inject end up in your breast milk and may harm your baby.

• Smoking cigarettes or chewing tobacco may reduce your milk production and inhibit the let-down reflex. It also may make your baby fussy or irritable. Babies who are exposed to secondhand smoke are at increased risk for many problems, including ear infections, asthma, and sudden infant death syndrome (SIDS). You should not smoke or be around those who do while you are pregnant or breast-feeding. If you smoke, do so as little as possible. Smoke outside and right after you have breast-fed, to give your baby the least exposure to the harmful chemicals.
• When a breast-feeding woman drinks alcohol heavily, it can cause a lack of energy and other health problems for her baby. One to two drinks per day have been linked to poor milk let-down and may affect the baby's muscle coordination. If you choose to drink alcohol, avoid breast-feeding or pumping milk right after you have had a drink. Wait 1 to 2 hours a drink, to allow your body to clear some of the alcohol from your system first.
• Illegal drugs can be passed to a baby in some amount through the breast milk. Drug use can cause poor milk let-down in the mother and a lack of energy, intoxication, hyperactivity, addiction, or other health problems in the infant. You can also face legal action if illegal drugs are found to have harmed your baby.