Caffeine does pass from the mother's milk to the baby and can cause agitation and sleeplessness in infants much as it does in adults. The dose effects of caffeine may differ from one mother-infant pair to another based on several factors. First, the amount of caffeine the mother drinks: Coffee has the highest amount of caffeine, then black tea, and then caffeinated soft drinks much less. Most babies do fine when their mother drinks one or two caffeine drinks a day, but some infants start showing symptoms of sleeplessness when their mother drinks four to six caffeine drinks a day. Secondly, although only one to 10 percent of the caffeine that the mother drinks ends up in her breast milk, young babies tend to store caffeine in their bodies. Infants may begin to show the symptoms of caffeine effect within hours after their mother drinks caffeine, and the symptoms may last for days. Babies over 4 months of age are better able to break down caffeine, so the symptoms may not last as long. To answer your question specifically, your 5-month-old baby may do fine if you limit yourself to one or two caffeine drinks a day. If she seems sleepless and agitated, stop the caffeine drinks and the symptoms should resolve in a few days. If your baby is already having sleeping problems or colic, you should probably avoid caffeine drinks for now.