How long does hydrochlorothiazide take to lower blood pressure?

Hydrochlorothiazide (HCTZ) is part of a class of medications called thiazide diuretics. Sometimes called water pills, these medications help remove excess fluid from the body. Also sold under the brand name Microzide, HCTZ is commonly used to treat hypertension (high blood pressure)—alone or in conjunction with other blood pressure medications. The medication will start to take effect just a few hours after you take it. However, it can take a week or two to meaningfully impact your blood pressure readings. HCTZ is also FDA approved to treat edema (fluid retention) caused by congestive heart failure, cirrhosis of the liver, estrogen therapy, and corticosteroid therapy.

How long does it take for hydrochlorothiazide to lower blood pressure? 

Hydrochlorothiazide “takes approximately two hours to reach peak effect,” explains Hosam Hmoud, MD, a cardiology fellow at Northwell Lenox Hill Hospital. However, it takes longer than that to reduce blood pressure. “I wouldn’t anticipate seeing a significant change in blood pressure for at least two weeks,” says Jean M. Cacciabaudo, MD, cardiologist medical director at Huntington Hospital. 

Hydrochlorothiazide works on a specific part of the kidneys by blocking the reabsorption of sodium (Na) and chloride (Cl) from the urine to the bloodstream. By increasing sodium and chloride excretion in the urine, water follows the excretion of Na and Cl, which helps to reduce the overall volume of fluid in the body, thus reducing blood pressure with consistent use over time.

As the medication starts working, you may not notice any difference in how you feel. However, you may need to use the bathroom more frequently. “Hydrochlorothiazide is a very gentle diuretic, and you may or may not see a notable increase in the frequency of urination,” Dr. Cacciabaudo notes. “It doesn’t cause the kind of urgency to urinate that other diuretics can have.” To track how it’s affecting your hypertension, try monitoring your blood pressure at home. Just don’t get discouraged if you don’t see immediate reductions, says Dr. Cacciabaudo.

What can affect how long it takes hydrochlorothiazide to work?

Several factors influence how the medication is absorbed and how long hydrochlorothiazide takes to work:

• Kidney disease: “Because hydrochlorothiazide is cleared by the kidneys, patients with kidney problems may have decreased clearance of hydrochlorothiazide, which can increase blood concentrations and duration of efficacy,” Dr. Hmound explains. In other words, the medication effects last longer between doses.
• Gastrointestinal disorders: “How quickly the drug is absorbed is largely due to gastrointestinal (GI) motility, how fast the stomach moves food/drugs/fluid through the entire GI tract,” says Bradley Serwer, MD, cardiologist and Chief Medical Officer at VitalSolution. Hydrochlorothiazide may work more slowly for people with conditions such as gastroesophageal reflux disease (GERD) that slow down digestion.
• Metabolism: Your unique body chemistry might cause you to metabolize hydrochlorothiazide more rapidly or slowly than others, says Dr. Cacciabaudo.
• Other medications: “Other medications can impact effectiveness, like other blood pressure medications, oral diabetes medications, steroids, and NSAIDs like ibuprofen,” explains Dr. Cacciabaudo. Tell your provider about any prescriptions or over-the-counter supplements you are taking to avoid a drug interaction with hydrochlorothiazide.
• Adherence: Forgetting to take your daily dose can make the medication less effective.

“Dosage amounts won’t affect the rate of onset,” says Dr. Hmoud. However, there are some things you can do to increase hydrochlorothiazide’s absorption. “Taking hydrochlorothiazide at the same time each day on an empty stomach helps the absorption and efficacy of the medication by maintaining a consistent drug concentration in the body,” explains Dr. Cacciabaudo.

What is the standard hydrochlorothiazide dosage?

Adults can take 12.5 mg to 100 mg of hydrochlorothiazide in a single dose or in divided doses throughout the day, according to the National Library of Medicine.

“The dosage of hydrochlorothiazide does vary based on what it is being used for,” says Kevin Rabii, DO, a cardiologist with Memorial Hermann in Houston, Texas. “For high blood pressure, the dosage usually varies from 12.5 mg to 50 mg daily.” The average dose of hydrochlorothiazide for the treatment of hypertension is 25 mg daily, says Dr. Cacciabaudo.

Often, healthcare providers start you on the lowest dose and then evaluate your blood pressure after two to four weeks. “If blood pressure goals are not met, your prescriber can increase hydrochlorothiazide to up to 50 mg once per day,” says Dr. Hmoud. Increased dosages will result in modest increases in blood pressure-lowering efficacy.”

Who should avoid taking hydrochlorothiazide?

While hydrochlorothiazide can be effective at lowering blood pressure, it’s not for everyone. Here’s what to know:

• Pregnant and breastfeeding women should use caution. The safety of hydrochlorothiazide for these groups is not proven, and high doses can lower milk supply.
• People who do not make urine, which is known as anuria, should not take hydrochlorothiazide.
• Caution should be used in people with gout, liver disease, diabetes, and kidney disease. Patients should have labs,  blood sugar, and kidney function monitored while taking the medication.

Hydrochlorothiazide can make you more prone to dehydration and electrolyte imbalances—specifically high calcium levels and low sodium, magnesium, and potassium levels.

Serious side effects of hydrochlorothiazide are not common, but they can happen:

• Trouble passing urine
• Extreme lightheadedness
• Passing out
• Signs of allergic reaction, such as rash, hives, trouble breathing, chest tightness, swelling of face, mouth, or throat

Seek immediate medical advice from a healthcare professional if you experience any of these side effects when taking hydrochlorothiazide.

The bottom line

Hydrochlorothiazide starts to work in your body within two to four hours of taking it. However, it may take several weeks to lower your blood pressure significantly. Kidney disease, gut motility, metabolism, other medications you are taking, and how regularly you take the medication can affect how quickly it works.