They are not performance-enhancing medicines in and of themselves, but are used to remove residues of other substances. Diuretics enhance urine output, and some athletes take them to cleanse away steroid residue. Others claim that the reduced weight gives them an advantage on demanding courses. However, due to the nature of these drugs they can have negative side effects such as dehydration, impaired cognitive function, etc. Athletes who use them should be very careful not to drink too much during exercise or risk suffering from diuresis (fainting due to excessive loss of water). Diuretics can be divided into two main groups: sulfonamide derivatives and benzenedicarboxylic acid derivatives. Both types work by reducing fluid retention in the body. Fluid retention is either a benefit for sportspeople, because it leads to lower body weights which usually means better performance, or a hindrance because it can cause problems with physical activity.