I believe that sertraline (Zoloft) in the breast milk is safer for the baby than either the mother’s depression or her stopping nursing.

In some earlier studies, Zoloft could not even be found in breast milk (Am J Psychiatry 1996 Sep;153(9):1132-7). We now know that the drug is present in tiny amounts. The highest concentrations are found in hindmilk (the high-fat milk that follows the initial foremilk, which contains more water) 7-10 hours after taking the tablet (Am J Psychiatry 1997 Sep;154(9):1255-60; J of Clin Psychiatry 2003 Jan;64(1):73-80). The lowest amounts are found in the hour prior to taking the Zoloft, which is usually a once-a-day medication. Overall, nursing infants receive less than 0.3 percent of mom's dose, even after adjusting for their weight (Br J Clin Pharmacol 1998 May;45(5):453-7).

No adverse events have been reported in babies exposed to Zoloft by breastfeeding. Where studied, developmental milestones have proceeded on course despite the fact that one baby was reported to have blood concentrations of Zoloft at half its mother's levels (Am J Psychiatry 1998 May;155(5):690-2).

If you are taking sertraline (Zoloft) and are not nursing often, the best time to nurse is during the hour before taking the pill. If you do need to nurse at the peak period of concentration, nursing for a brief period, and discarding the hindmilk, can also reduce the amount of drug the baby receives. Hindmilk is especially rich in nutrients, so it should not be discarded at other times of the day unless there are other sources of nutrition.