The CDC's Healthy People 2010, which is a set of national health goals, includes targets for breastfeeding. They are that 50% of moms will breastfeeding at 6 months and at least 25% will still be breastfeeding at 12 months.
While there are a lot of reasons moms stop nursing before they meet these goals, including having problems getting their baby to latch on, thinking they aren't making enough milk, or going back to work, being prescribed a new medicine shouldn't usually be one of them. With a little research, you and your doctor can usually find medicines that are compatible with breastfeeding.
Remember that the American Academy of Pediatrics (AAP) states that "most drugs likely to be prescribed to the nursing mother should have no effect on milk supply or on infant well-being." The AAP even publishes a long list of medicines that are usually compatible with breastfeeding and a much shorter list of medicines to avoid.
Drugs and Lactation Database (LactMed)
The AAP recommendations, and just about everything else that is known about drugs and breastfeeding, is included in the Drugs and Lactation Database. In addition to an easy to reason summary about common medicines and breastfeeding, LactMed provides information on the drugs effects on the baby, possible effects on breastmilk production, the AAP category, and alternate medicines to consider.
Sources:
AAP. Policy Statement. The Transfer of Drugs and Other Chemicals Into Human Milk. PEDIATRICS Vol. 108 No. 3 September 2001, pp. 776-789.
Centers for Disease Control and Prevention. Healthy People 2010. Maternal, Infant, and Child Health. Breastfeeding, Newborn Screening, and Service Systems.
