The human body is 60 percent water . In organisms, water is divided into fluids outside and inside cells. The amount of fluid outside cells depend mainly on the amount of natrium ions but also on the amount of chlorine ions that maintain the osmotic pressure.
The function of kidneys is, among other things, to remove substances from the blood that are foreign to the organism, and waste products and to maintain a consistent osmotic pressure in the body. Kidneys are the natrium content controller of the body.
The glomeruli of kidneys (the functional units) form primary urine of about 180 liters per day that contains water and electrolytes. Most of the urine is absorbed back into the body from the duct system of kidneys. The part of the primary urine that isn't absorbed back leaves the body as urine.
Diuretics are medical substances whose functioning mechanism is to prevent the back-absorption of electrolytes and water in kidneys. As a consequence of this, the secretion of water and salts to the urine increases. 
Diuretics include several different medical substances that differ from each other, among others, by their chemical structure and functioning mechanism. Diuretics are divided into thiazide diuretics and their derivative, short-acting salt diuretics, diuretics that contain potassium, and other diuretics .
Diuretics in the thiazide group include hydrochlorothiazide. Furosemide and bumetanide are short-acting salt diuretics (loop diuretics). Spironolactone, triamterene and amiloride are potassium sparing diuretics. Other diuretics include, for example, carbonic anhydrase inhibitors, such as acetazolamide and dorzolamide, and osmotic diuretics, such as mannitol that causes water diuresis.
Diuretics are used for the treatment of increased blood pressure, cardiac failure and swelling, as well as for other conditions [2, 3]. For the medicinal treatment of high blood pressure, diuretics are used that increase the excretion of sodium and chloride in the urine . Treatment of cardiac failure using diuretics aims at decreasing water and salt content in body, in which treatment the blood amount also decreases.
Salt diuretics are used especially in situations that require quick and effective diuresis . These situations include the treatment of pulmonary edema, hypertensive crises and poisonings. Salt diuretics are used also for the treatment of cardiac failure .
The effect of potassium sparing diuretics is less effective in comparison with other diuretics; therefore, in the treatment of increased blood pressure they are used with thiazide diuretics.
Properties and mechanism of action
The properties of different diuretics differ from each other . Salt diuretics are more effective than thiazide diuretics, whereas the potassium sparing diuretics are less effective than other diuretics . Also the mechanisms of effect of diuretic groups differ from each other .
However, as a general rule, it can be said that diuretics prevent the re-absorption of electrolytes and water in the kidneys and therefore the excretion of urine and electrolytes increases.
Thiazide diuretics increase the excretion of natrium, potassium, chloride and water. Salt diuretics increase the excretion of calcium, as well as natrium, potassium, chloride and water in urine. Among the potassium sparing diuretics, spironolactone increases the excretion of natrium and water in urine and at the same time decreases potassium excretion in urine. Triamterene and amiloride inhibit the re-absorption of natrium from the kidneys and decrease potassium excretion in urine.
Diuretics remove water and salts  from the body; therefore, they are used to lose weight in competitive sports with weight categories .
Diuretics are also used in the effort to hide the presence of doping substances in urine because diuretics increase the amount of urine so therefore the concentration of other substances in urine decreases. Certain diuretics can also hide the use of other doping substances by changing the pH of urine in a manner in which the doping substances won’t necessarily excrete in urine.
Use of large doses of diuretics can create severe dehydration and hypovolaemia in the body, meaning that the blood volume is reduced below the normal level [2, 3].
The adverse effects caused by thiazide diuretics include, among others, fluid and electrolyte imbalances . The most remarkable adverse effect of thiazide diuretics is hypokalaemia, potassium content in blood that is below normal levels. Large doses of thiazide diuretics may cause dehydration and hypotonia, meaning an excessive decrease in blood pressure.
Use of thiazide diuretics may sometimes also aggravate diabetes and lead to an increased risk of getting gout , because thiazides affect the renin-angiotensin system, and the glucose and uric acid concentrations in blood can increase during the thiazide treatment [2, 3]. Other adverse effects are also reported .
The adverse effects of short-acting salt diuretics are, besides body dehydration, fluid and electrolyte imbalances, especially hypokalaemia . Short-acting salt diuretics, similarly to thiazide diuretics, might also aggravate diabetes and increase the risk of getting gout.
The most important adverse effect of potassium sparing diuretics is hyperkalaemia in which the potassium level in the blood is too high . Hyperkalaemia can cause death.
The use of medicines for doping is regarded as medicine abuse, which means that the use differs from that stated and found in the instructions for use .