Skip to main content

Metahydrin Side Effects

Generic name: trichlormethiazide

Note: This document contains side effect information about trichlormethiazide. Some dosage forms listed on this page may not apply to the brand name Metahydrin.

Applies to trichlormethiazide: oral tablet.


Metabolic changes associated with trichlormethiazide (the active ingredient contained in Metahydrin) as with other thiazide diuretics, are relatively common, especially when daily doses greater than 4 mg are used. Mild hypokalemia (decrease of 0.5 mEq/L) occurs in up to 50%, and may increase the risk of cardiac arrhythmias. Metabolic alkalosis, hyponatremia, hypomagnesemia, hypophosphatemia, hypercalcemia, hyperglycemia hypercholesterolemia, and hyperuricemia are also relatively common. The electrolyte and intravascular fluid shifts that may occur during trichlormethiazide diuresis can provoke hepatic encephalopathy in patients with hepatic cirrhosis.[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 hypercalcemia, milk-alkali syndrome (hypercalcemia, metabolic alkalosis, and renal insufficiency) have been associated with the use of a related drug, chlorothiazide.[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 have been associated with thiazide-induced diuresis.[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]


Gastrointestinal side effects 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]

A retrospective case-controlled 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. Trichlormethiazide-induced hypercholesterolemia or hypertriglyceridemia may enhance the formation of some types of gallstones.[Ref]


Renal side effects including new or worsened renal insufficiency associated with trichlormethiazide (the active ingredient contained in Metahydrin) 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 the use of some thiazide diuretics.[Ref]


Endocrinologic changes associated with thiazide diuretics 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]

Nervous system

Nervous system side effects are rare, and include general fatigue, visual disturbances and insomnia.[Ref]


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


Musculoskeletal cramping or spasms have occasionally been associated with trichlormethiazide (the active ingredient contained in Metahydrin) diuresis.[Ref]


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


1. Kansal PC, Buse J, Buse MG (1969) "Thiazide diuretics and control of diabetes mellitus." South Med J, 62, p. 1372-9

2. Seltzer HS, Allen EW (1969) "Hyperglycemia and inhibition of insulin secretion during administration of diazoxide and trichlormethiazide in man." Diabetes, 18, p. 19-28

3. Takeda R, Ueno T, Tsutchiya M, Kawasaki S, Masuya H (1975) "Sinus arrest following diuretic therapy in a patient with myxedema and hypertension." Cardiology, 60, p. 185-91

4. el-Meheiry MM, Nabih AE, Soliman MD (1966) "A clinical study of a new diuretic, Trichlormethiazide." J Trop Med Hyg, 69, p. 209-14

5. Coe FL, Kavalach AG (1974) "Hypercalciuria and hyperuricosuria in patients with calcium nephrolithiasis." N Engl J Med, 291, p. 1344-50

6. (2001) "Product Information. Metahydrin (trichlormethiazide)." Hoechst Marion Roussel

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

8. Stokkeland OM, Sangvik K, Ditlefsen EM (1975) "A comparative study of metoprolol and trichlormethiazide in hypertension." Curr Ther Res Clin Exp, 18, p. 755-68

9. Jinnouchi T, Mimura G, Sadanaga T, Ono K, Sakamoto Y (1976) "Proceedings: Study on the effect of long-term administration (one year) of trichlormethiazide upon glucose metabolism of SHR." Jpn Heart J, 17, p. 412-3

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.