How do diuretics cause weight loss?

Increase urination. Diuretics are a class of drugs that cause the kidneys to excrete a larger volume of urine. This can be a beneficial effect in patients with high blood pressure, congestive heart failure or soft tissue fluid retention.These are not generally used for weight loss except in those individuals retaining extra fluid.Can cause dehydration and electrolyte abnormalities in normal pts trying to lose weight.
Urinating more water. Diuretics cause temporary weight loss by making a person urinate (pee) out more urine. Urine is almost all water, and weighs 8 pounds a gallon. However, if after excess urination, a person doesn't drink water to replenish himself, his body will be dehydrated and weak. He will be thirsty and have to drink back the same amount of water he pee'd out, in order to return his body chemistry to balance.