Still others may have legitimate medical reasons that they cannot breastfeed. The WHO lists only a few of these, including HIV infection, necessary maternal medications that aren't safe for infants (like psychotherapeutics or chemotherapy), tuberculosis, substance use (like alcohol, nicotine, cocaine, amphetamines, etc.), or other serious maternal illnesses. Some babies may also not be able to handle breast milk. Infants who have phenylketonuria need a formula free of phenylalanine, others may need galactose-free or leucine/isoleucine/valine-free formulas. These babies might be at higher risk for the diseases and infections mentioned earlier, but the risks of continuing to feed them breast milk are clearly not worth the protective effects.