safe storage time limits. Comparison to other milks All mammalian species produce milk, but the composition of milk for each species varies widely and other kinds of milk are often very different from human breast milk. As a rule, the milk of mammals that nurse frequently (including human babies) is less rich, or more watery, than the milk of mammals whose young nurse less often. Human milk is noticeably thinner and sweeter than cow's milk. Whole cow's milk contains too little iron, retinol, vitamin E, vitamin C, vitamin D, unsaturated fats or essential fatty acids for human babies. Whole cow's milk also contains too much protein, sodium, potassium, phosphorus and chloride which may put a strain on an infant's immature kidneys. In addition, the proteins, fats and calcium in whole cow's milk are more difficult for an infant to digest and absorb than the ones in breast milk. The composition of marsupial and monotreme milk contains essential nutrients, growth factors and immunological properties to support the development of joeys and puggles. Note: Milk is generally fortified with vitamin D in the U.S. and Canada. Non-fortified milk contains only 2 IU per 3.5 oz. Effects of medications and other substances on milk content Almost all medicines pass into breastmilk in small amounts by a concentration gradient. The amount of drug bound by maternal plasma proteins, the size of the drug molecule, the pH of the drug, and the lipophilicity of the drug determine whether the medication will pass into breastmilk. Medications that are non-protein bound, low in molecular weight, or highly lipid-soluble are more likely to enter the breast milk in larger quantities. Some have no effect on the baby and can be used while breastfeeding, while other medications may be harmful to the infant. Some generally safe medications that the mother can use while breastfeeding include: On the other hand, there are medications that may be toxic to the baby while breastfeeding and thus should not be used in breastfeeding mothers, such as: Furthermore, drugs of abuse, such as cocaine, amphetamines, heroin, and marijuana cause adverse effects on the infant during breastfeeding. Adverse effects include seizures, tremors, restlessness, and diarrhea. To reduce infant exposure to medications used by the mother, use topical therapy or avoid taking the medication during breastfeeding times when possible. Hormonal products and combined oral contraceptives should be avoided during the early postpartum period as they can