Hydrochlorothiazide: brand name vs generic

When it comes to getting prescription medications, it may seem daunting to take the generic option when you know a brand name is available. But generic drugs aren't like knock-off designer shoes. They must adhere to the same stringent guidelines as the brand name medications. 

The government knows that taking a prescription drug is serious, so they ensure that companies can't sell you a lower-quality product while making it look like the real thing. In fact, the U.S. Food and Drug Administration (FDA) requires that pharmaceutical companies that want to produce generic drugs prove that they're the same as the brand-name medication (FDA, 2018). 

These generic drugs have to be just as safe and effective as the original brand-name prescription medication and be offered in the same strengths and dosage forms as the brand name option (FDA, 2018).

That's the case with hydrochlorothiazide (HCTZ), a thiazide diuretic (aka a "water pill") used to treat high blood pressure or swelling (edema) by helping your body get rid of excess water and salt. It's sold as a generic drug and under the brand names Microzide, HydroDiuril, and Oretic. Generic forms may also be called "generic Microzide."

You may also see HCTZ as an ingredient of medications that combine it with other blood pressure-lowering medications. Research has shown that thiazide diuretics such as HCTZ may be used in combination with beta-blockers, ACE inhibitors, angiotensin receptor blockers (ARBs), and calcium channel blockers to effectively lower blood pressure (Sica, 2011). That means HCTZ is in many different brand-name prescription medications. Not all of these combination medications are available as generic drugs (Cooper-DeHoff, 2013). 

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Hydrochlorothiazide is a prescription medication used to treat high blood pressure (hypertension). Thiazide diuretics such as HCTZ help the body get rid of extra salt and water, reducing water retention in the body and blood volume. This lowers the pressure in the blood vessels (like letting some water out of a water balloon), making it easier for your heart to pump your blood through your body. The excess water is released from your body in your urine, so you may notice that you have to pee more frequently when you start taking it.

There are many different options when it comes to diuretics, and your healthcare provider will decide which treatment is best for you. Though they all reduce how much water is retained in the body, they each accomplish this by acting on the kidneys differently. Thiazide diuretics are generally the first diuretics prescribed to help lower blood pressure, with the exception of people who have chronic kidney disease (CKD) (Whelton, 2018).

The U.S. Food and Drug Administration (FDA) approved hydrochlorothiazide to treat high blood pressure as well as swelling (edema) in patients with a condition called congestive heart failure or those with kidney disease (FDA, 2011). Prescription drugs that combine HCTZ with beta-blockers, ACE inhibitors, angiotensin receptor blockers (ARBs), and calcium channel blockers are used to further lower blood pressure when a diuretic alone is not enough (Sica, 2011).

HCTZ may also be used off-label to prevent kidney stones and to help people with diabetes insipidus, a medical condition characterized by an imbalance of salts and fluids in the body (NIH, 2019; UpToDate, n.d.). Diabetes insipidus (DI) is not the same as diabetes mellitus (high blood sugar). Patients with DI lose too much water in their urine, resulting in low blood pressure. HCTZ can be used to regulate this condition and alleviate excess water loss for these patients (Bichet, 2019). 

Since HCTZ reduces the amount of water in your body by sending it to the kidneys to be removed as urine, you will notice that after you start taking it, you need to pee more frequently. Other common side effects of hydrochlorothiazide include constipation or diarrhea, headache, erectile dysfunction, loss of appetite, nausea, vomiting, vision problems, and weakness. The higher the dose you're taking, the greater the chance of side effects (DailyMed, 2014). 

One study showed that patients taking 12.5 mg daily reported the same rate of side effects as those given a placebo. Adverse effects happened more frequently in those taking doses of 25 mg or more in clinical trials (DailyMed, 2014).

This medication may also cause high uric acid levels (hyperuricemia). The buildup of uric acid in the body can lead to the development of a condition known as gout -- a painful type of arthritis characterized by sudden pain, redness, and swelling of the joints (Jin, 2012). For people with a history of gout, hydrochlorothiazide may make symptoms worse (DailyMed, 2014).

Since hydrochlorothiazide is used to lower blood high blood pressure, in some cases, it can cause dangerously low blood pressure, a condition known as hypotension. Symptoms of low blood pressure can include dizziness or lightheadedness, blurred vision, fatigue, shallow breathing, rapid heart rate, confusion, and fainting. Drinking alcohol may increase your chances of experiencing low blood pressure while taking hydrochlorothiazide (DailyMed, 2014).

Serious side effects

Hydrochlorothiazide affects electrolyte and fluid balance in the body, which can cause serious side effects. This medication may cause low sodium levels (hyponatremia), low potassium levels (hypokalemia), and low magnesium levels (hypomagnesemia). These electrolyte imbalances can cause symptoms such as dry mouth, irregular heartbeats (arrhythmias), muscle aches, nausea, thirst, tiredness, vomiting, and weakness. In some cases, these conditions can be dangerous and even life-threatening (DailyMed, 2014). 

If you experience any symptoms of an electrolyte imbalance such as dry mouth, weakness, restlessness, confusion, or muscle pains, or loss of consciousness, seek medical attention (NIH, 2019).

There have been reports of allergic reactions to HCTZ (FDA, 2011). This diuretic is a sulfonamide, a medication that uses sulfa, so people with an allergy to sulfa drugs should not take hydrochlorothiazide. An allergic reaction may cause hives, shortness of breath, trouble breathing, wheezing, skin rash, or swelling of the face, tongue, or throat. Seek medical attention immediately if you experience any of these signs of an allergic reaction. 

The generic form and brand name versions of HCTZ are available as tablets in 12.5 mg, 25 mg, and 50 mg dosages. These medications are typically taken once a day. Medications that combine HCTZ with other drugs use both 12.5 mg and 25 mg dosages for the diuretic. Higher doses of HCTZ are accompanied by higher doses of the other drug included in these medications.

All forms of HCTZ medication, as well as the combination drugs, should be stored at room temperature out of the reach of children. In the case of a missed dose, the dose should be taken as soon as possible unless it's almost time for the next dose. In that case, only take the next dose as scheduled (NIH, 2019).

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Current version

September 14, 2020

Written by

Linnea Zielinski

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.