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Chlorothiazide Side Effects

Medically reviewed by Last updated on Dec 24, 2023.

Applies to chlorothiazide: oral suspension, oral tablet. Other dosage forms:

Serious side effects of Chlorothiazide

Along with its needed effects, chlorothiazide may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking chlorothiazide:

Incidence not known

Other side effects of Chlorothiazide

Some side effects of chlorothiazide may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

For Healthcare Professionals

Applies to chlorothiazide: intravenous powder for injection, oral suspension, oral tablet.


Metabolic changes associated with chlorothiazide, as with other thiazide diuretics, are relatively common, especially when daily doses greater than 500 mg are used. Mild hypokalemia (decrease of 0.5 mEq/L) occurs in up to 50%, and may predispose patients to cardiac arrhythmias. Metabolic alkalosis, hyponatremia, hypomagnesemia, hypophosphatemia, hypercalcemia, hyperglycemia, hypercholesterolemia, and hyperuricemia are also relatively common.[Ref]

Hyperuricemia may be an important consideration in patients with a history of gout. Hypophosphatemia and low serum magnesium concentrations may occur, but are usually clinically insignificant except in malnourished patients.

Rare cases of the milk-alkali syndrome (hypercalcemia, metabolic alkalosis, and renal insufficiency) have been associated with chlorothiazide.

Chlorothiazide-induced hypercalcemia appears to depend on circulating parathyroid hormone.[Ref]


Cardiovascular complications of diuretic therapy include orthostatic hypotension secondary to intravascular volume depletion. This has resulted in syncope and, in some patients with glaucoma, temporary loss of vision. Rare cases of cerebrovascular accident associated with thiazide-induced diuresis have been reported.[Ref]


Hypersensitivity reactions usually involve the skin (cutaneous vasculitis, urticaria, rash, purpura), but may involve the gastrointestinal system (nausea, vomiting, or diarrhea), the genitourinary system (interstitial nephritis), and the respiratory system (acute noncardiogenic pulmonary edema, pneumonitis). Thiazide diuretics may induce phototoxic dermatitis.[Ref]

Thiazides may induce allergic reactions in patients who are allergic to sulfonamides.[Ref]


Dermatologic reactions may indicate hypersensitivity to the drug. Erythema multiforme, Stevens-Johnson syndrome, exfoliative dermatitis (including toxic epidermal necrolysis), and alopecia have been reported in rare cases.[Ref]


A retrospective case-control drug surveillance study has revealed the relative risk of acute cholecystitis associated with the use of a thiazide diuretic is 2.0. The suspected explanation for this association is the potentially deleterious effect thiazides have on the serum lipid profile. Chlorothiazide-induced hypercholesterolemia or hypertriglyceridemia may enhance the formation of some types of gallstones.[Ref]

Gastrointestinal problems include diarrhea, vomiting, constipation or abdominal pain in approximately 5% of patients. Thiazide diuretics have been associated with acute cholecystitis and rare cases of pancreatitis.[Ref]


Renal side effects including new or worsened renal insufficiency associated with chlorothiazide therapy is a probable sign of intravascular volume depletion, and serves as a signal to reduce or withhold therapy. Rare cases of allergic interstitial nephritis have been associated with chlorothiazide.[Ref]


Endocrinologic changes associated with chlorothiazide, as with other thiazide diuretic agents, include decreased glucose tolerance and a potentially deleterious effect on the lipid profile. This may be important in some patients with or who are at risk for diabetes or coronary artery disease.[Ref]


Hematologic side effects are rare. Rare cases of immune-complex hemolytic anemia, aplastic anemia, and thrombocytopenia have been associated with thiazide diuretics.[Ref]


Musculoskeletal cramping or spasms have occasionally been reported during chlorothiazide diuresis.[Ref]


Genitourinary problems have been limited to rare complaints of impotence among male patients.[Ref]

Frequently asked questions


1. Lindy S, Tarssanen L. Serum calcium and phosphorus in patients treated with thiazides and furosemide. Acta Med Scand. 1973;194:319-22.

2. Aneckstein AG, Weingold AB. Chlorothiazide-induced hepatic coma in pregnancy. Am J Obstet Gynecol. 1966;95:136-7.

3. Gammon GD, Docherty JP. Thiazide-induced hypercalcemia in a manic-depressive patient. Am J Psychiatry. 1980;137:1453-5.

4. Leigh H. Letter: Factitious hypokalemia. Ann Intern Med. 1974;80:111-2.

5. Parfitt AM. Thiazide-induced hypercalcemia in vitamin D-treated hypoparathyroidism. Ann Intern Med. 1972;77:557-63.

6. Jackson WP, Nellen M. Effect of frusemide on carbohydrate metabolism, blood-pressure, and other modalities. A comparison with chlorothiazide. Br Med J. 1966;2:333-6.

7. Lapidus PW, Guidotti FP. Gout in orthopaedic practice: review of 232 cases. Clin Orthop. 1963;28:97-110.

8. Popovtzer MM, Subryan VL, Alfrey AC, Reeve EB, Schrier RW. The acute effect of chlorothiazide on serum-ionized calcium. Evidence for a parathyroid hormone-dependent mechanism. J Clin Invest. 1975;55:1295-302.

9. Paloyan E, Farland M, Pickleman JR. Hyperparathyroidism coexisting with hypertension and prolonged thiazide administration. JAMA. 1969;210:1243-5.

10. Parfitt AM. Chlorothiazide-induced hypercalcemia in juvenile osteoporosis and hyperparathyroidism. N Engl J Med. 1969;281:55-9.

11. Moore TD, Bechtel TP. Hyponatremia secondary to tolbutamide and chlorothiazide. Am J Hosp Pharm. 1979;36:1107-10.

12. Gora ML, Seth SK, Bay WH, Visconti JA. Milk-alkali syndrome associated with use of chlorothiazide and calcium carbonate. Clin Pharm. 1989;8:227-9.

13. Sherlock S, Senewiratne B, Scott A, Walker JG. Complications of diuretic therapy in hepatic cirrhosis. Lancet. 1966;1:1049-52.

14. Sherlock S, Walker JG, Senewiratne B, Scott A. The complications of diuretic therapy in patients with cirrhosis. Ann N Y Acad Sci. 1966;139:497-505.

15. Product Information. Diuril (chlorothiazide). Merck & Co., Inc. 2001;PROD.

16. Pickkers P, Schachter M, Hughes AD, Feher MD, Sever PS. Thiazide-induced hyperglycaemia: a role for calcium-activated potassium channels? Diabetologia. 1996;39:861-4.

17. Bullock JD. Antihypertensive drugs and danger to vision . JAMA. 1977;237:2186.

18. Stern RS, Kleinerman RA, Parrish JA, et al. Phototoxic reactions to photoactive drugs in patients treated with PUVA. Arch Dermatol. 1980;116:1269-71.

19. Bowden FJ. Non-cardiogenic pulmonary edema after ingestion of chlorothiazide. BMJ. 1989;298:605.

20. Lyons H, Pinn VW, Cortell S, Cohen JJ, Harrington JT. Allergic interstitial nephritis causing reversible renal failure in four patients with idiopathic nephrotic syndrome. N Engl J Med. 1973;288:124-8.

21. Chan HL. Fixed drug eruptions. A study of 20 occurrences in Singapore. Int J Dermatol. 1984;23:607-9.

22. Rosenberg L, Shapiro S, Slone D, Kaufman DW, Miettinen OS, Stolley PD. Thiazides and acute cholecystitis. N Engl J Med. 1980;303:546-8.

23. Goldman JA, Neri A, Ovadia J, Eckerling B, Vries A, de. Effect of chlorothiazide on intravenous glucose tolerance in pregnancy. Am J Obstet Gynecol. 1969;105:556-60.

24. Bird CC, Reeves BD. Effect of diuretic administration on urinary estriol levels in late pregnancy. Am J Obstet Gynecol. 1969;105:552-5.

25. Miller NR, Moses H. Transient oculomotor nerve palsy. Association with thiazide-induced glucose intolerance. JAMA. 1978;240:1887-8.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.