Thiazides are not approved for treatment or prevention of osteoporosis. It makes sense to use them in patients with hypercalciuria and osteopenia, and in patients with osteopenia who can't take other choices. Patients with hypertension who use this therapy will probably have benefit on both blood pressure and bone.
Hydrochlorothiazide or chlorthalidone, 12.5 to 25 mg/day. In elderly people, who are most likely to have osteoporosis, higher doses will result in more side effects.
Remember that "loop" diuretics, such as Lasix or furosimide, have the OPPOSITE effect on the calcium, and will tend to make bone disease worse.
Thiazide diuretics have been used by millions of people for decades. Compared to other drugs, they have a good safety profile. In the recent large ALLHAT hypertension trial, about 18% of subjects had a symptomatic side effect or abnormal lab test that caused them to stop the medication. Whenever a drug has been around for so many years, used by so many people, there will be a long list of very rare side effects, such as liver failure or thrombocytopenia. The following are side effects attributed to thiazides:
Hypercalcemia has been reported with thaizides; if this occurs with low doses, a careful evaluation of calcium metabolism must be done to see if there is another cause of hypercalciuria or osteoporosis (for example, hyperparathyroidism or sarcoidosis).