Key takeaways

Hydrochlorothiazide (HCTZ) is a diuretic medication primarily used to treat high blood pressure and edema, which works by increasing the elimination of water and salt through urine.
Common side effects of hydrochlorothiazide include electrolyte imbalances like low potassium and sodium levels, increased sun sensitivity leading to a higher risk of certain skin cancers, and potential for serious allergic or skin reactions.
Long-term or serious side effects can include dangerously low potassium levels, kidney dysfunction or failure, and an increased risk of non-melanoma skin cancer, particularly in patients with white skin.
To minimize side effects, patients are advised to follow prescription directions carefully, avoid excessive sun exposure and use sunscreen, stay hydrated, and regularly consult healthcare providers for follow-up tests and appointments.

Hydrochlorothiazide (HCTZ) is a generic drug commonly prescribed to lower blood pressure in people diagnosed with high blood pressure, but it is also used to reduce swelling of the extremities due to congestive heart failure, ascites, or treatment with corticosteroids or estrogen. As a thiazide diuretic (water pill), hydrochlorothiazide increases the elimination of water and salt through the urine. This helps to bring down blood pressure. Many of hydrochlorothiazide’s side effects are related to its diuretic effects. Some side effects are avoidable, some can be minimized, and others may require medical intervention.

Common side effects of hydrochlorothiazide

The most common side effect of hydrochlorothiazide is low potassium levels, a direct effect of the drug’s diuretic effects. Anywhere from 1/3 to ½ of people taking hydrochlorothiazide will eventually have depleted potassium levels. Many of the other common side effects are also related to the body’s increased elimination of water and electrolytes:

Low potassium
Low sodium
Low magnesium
Elevated calcium
Low chloride
Elevated blood sugar
Elevated cholesterol and fat levels
Elevated uric acid levels
Orthostatic hypotension (dizziness and vertigo when standing)
Dizziness
Diarrhea
Abdominal pain
Weakness
Headache
Hair loss
Rash

Serious side effects of hydrochlorothiazide

Hydrochlorothiazide’s most serious side effects include:

Dangerously low potassium levels
Electrolyte imbalance
Sun sensitivity
Abnormal heartbeats
Swollen pancreas
Skin cancer
Kidney dysfunction
Kidney failure
Anemia
Low white blood cell counts (which can interfere with the body’s ability to fight infection)
Low platelet levels (which can cause bruising or bleeding)
Angle-closure glaucoma
Worsening of lupus
Severe allergic reactions or serious skin reactions

Weight changes

Hydrochlorothiazide eliminates more water from the body than usual, so body weight may decrease. That’s nice to see on a bathroom scale, but it isn’t fat or muscle weight. It’s water weight. When hydrochlorothiazide is stopped, the water weight will probably return in short order.

Electrolyte imbalance

Electrolyte imbalances are a common and sometimes serious side effect of hydrochlorothiazide. The drug can deplete the body of one or more electrolytes, including sodium, potassium, magnesium, and chloride. It can also increase calcium levels. The effects seem to be dose-related. While the incidence of electrolyte problems has not been determined, they are common enough that people taking hydrochlorothiazide need to be periodically tested for electrolyte levels, particularly potassium. People taking hydrochlorothiazide should know the signs of electrolyte depletion, particular hypokalemia, or low potassium, such as weakness, fatigue, muscle cramps, and constipation. Contact a healthcare professional if any of these symptoms are noticed.

Sun sensitivity

Hydrochlorothiazide is associated with an increased risk of certain skin cancers. The medication causes sun sensitivity. Patients who take hydrochlorothiazide should visit their dermatologist on a regular basis for skin screenings. Also, people who take this drug should avoid tanning beds and avoid the sun when possible. When in the sun, it is important to wear protective clothing and apply and reapply sunscreen (of at least SPF 30) frequently.

Severe allergic or skin reactions

In rare cases, a serious allergic or skin reaction may occur. These reactions can be life-threatening or cause death. If you notice any of the following symptoms, get emergency medical help right away. Symptoms of a serious allergic reaction can include hives, difficulty breathing, or swelling of the face, lips, tongue, or throat. Symptoms of a serious skin reaction may include sore throat, fever, burning eyes, red or purple rash, or blistering or peeling skin.

Chest pain

Hydrochlorothiazide has not been associated with causing or worsening chest pain. However, it is frequently combined with other blood pressure drugs that may worsen chest pain. When taking more than one prescription drug, it’s sometimes difficult to determine which drug is responsible for individual side effects. Chest pain is a serious symptom, so make sure to tell the prescribing healthcare provider.

Joint pain

Joint pain is not a side effect of hydrochlorothiazide. However, the drug can worsen some types of existing joint diseases. Because hydrochlorothiazide reduces the fluid volume of blood, it results in a percentage increase of other substances in the blood like uric acid. If uric acid levels get high enough, the excess crystallizes in the joints. This can cause or worsen gout, an arthritic condition due to uric acid crystals building up in the joints. How often hydrochlorothiazide contributes to gout flare-ups is unknown, but the joint pain is certainly painful and sometimes debilitating.

Hair loss

Thinning hair is a side effect of thiazide diuretics. The hair loss won’t happen all at once as it does with some drugs, such as cancer drugs. Instead, it will take a few months. The incidence is unknown, but remember that hydrochlorothiazide is typically used with other blood pressure drugs. One type of blood pressure drug, beta blockers, are also associated with hair loss and hair thinning. The good news is that drug-induced hair loss is usually reversible once the offending drug has been stopped.

How soon do hydrochlorothiazide side effects start?

Hydrochlorothiazide’s diuretic effects begin within an hour or two of taking the capsule or tablet and peak in one to five hours. Some side effects may appear during that time, including diarrhea, nausea, and vomiting. Allergic reactions, however, could happen very rapidly even after taking the first dose. Many other side effects are delayed and could take days, weeks, or months to manifest.

How long do hydrochlorothiazide side effects last?

The body will adapt to hydrochlorothiazide, so some side effects may get better over time as you get used to the medicine. Those that don’t will mostly resolve after the drug has been stopped, particularly the most common side effects. Even hair loss is often reversible when caused by drugs like hydrochlorothiazide.

What are the long-term side effects of hydrochlorothiazide?

Most of hydrochlorothiazide’s side effects will get better after the drug has been stopped. Some may require time to get better, such as allergic reactions or gout. Some side effects such as skin cancer or kidney damage may have long-term or lifelong consequences.

Hydrochlorothiazide contraindications

Hydrochlorothiazide is too dangerous for some people to take:

Kidney problems: people with reduced kidney function (creatinine clearance of less than 10 mL/minute; although some references recommend not using hydrochlorothiazide if creatinine clearance is under 30) or inability to produce urine (anuria) cannot take hydrochlorothiazide without risking kidney damage or failure
Newborns with jaundice: Jaundice can be worsened in newborns who are given hydrochlorothiazide
Allergies: People allergic to hydrochlorothiazide or sulfa drugs cannot safely take the drug

Pregnancy

Hydrochlorothiazide is not restricted for use in pregnant women. In terms of risk, it’s in the same category as acetaminophen and prenatal vitamins. However, it is considered a risk to the fetus in women with pre-eclampsia or similar placental problems and generally should not be used. Anyone who is pregnant or planning to become pregnant should consult their healthcare provider for medical guidance before taking hydrochlorothiazide.

Breastfeeding

A healthcare professional might suggest other treatment options for breastfeeding women, though hydrochlorothiazide (at lower doses) is not contraindicated in those cases. Nursing babies could develop serious problems from the small amounts of hydrochlorothiazide present in breast milk. In addition, hydrochlorothiazide may affect breast milk production. In fact, it is often used off-label in higher doses to suppress lactation.

Children

Hydrochlorothiazide is FDA-approved for use in children as young as newborns.

Hydrochlorothiazide warnings

Like all diuretics, hydrochlorothiazide may cause problems because of pre-existing health conditions or other issues.

Cautions

Hydrochlorothiazide can cause problems in people with certain medical conditions. In some cases, hydrochlorothiazide may worsen the condition, like gout, or bring it on a second time, like pancreatitis. These medical or physical conditions include:

Diabetes
Electrolyte problems
Dehydration
A history of gout
A history of swollen pancreas
Liver or kidney problems
Irregular heartbeats
A history of seizures
Lupus

In addition, hydrochlorothiazide may cause problems in older patients including low sodium and falls. Finally, the risk for non-melanoma skin cancer goes up when taking hydrochlorothiazide, a risk that is greatest for white patients.

Abuse and dependence

Hydrochlorothiazide is not associated with drug abuse, dependence, or withdrawal.

Overdose

A hydrochlorothiazide overdose can cause a hazardous depletion of electrolytes, so immediate medical care is needed if an overdose is suspected. The symptoms of an overdose may include:

Nausea
Dizziness
Weakness
Muscle pain
Dry mouth/thirst

The maximum dosage will depend on age and the condition being treated. The maximum adult dose for hypertension is 50 mg per day; for fluid retention, the maximum daily dose is 100 mg.

Recalls

Hydrochlorothiazide recalls are rare and limited to quality problems at individual manufacturers.

Hydrochlorothiazide interactions

People using hydrochlorothiazide often are taking other drugs. Some of these can be risky when taken with hydrochlorothiazide:

Other blood pressure medications, though commonly prescribed with hydrochlorothiazide, increase the risk for low blood pressure
Corticosteroids such as prednisone increase the risk of electrolyte loss when taking thiazide diuretics
Bile resins (such as cholestyramine) can make it harder for the body to absorb hydrochlorothiazide
Antidiabetic drugs may be less effective because thiazide diuretics can increase blood sugar levels
Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, and naproxen may reduce the effectiveness of hydrochlorothiazide and increase the risk of kidney damage
Some drugs like aminoglycoside antibiotics and lithium can damage the kidneys; they are more likely to damage the kidneys when taken with a diuretic
Barbiturates, sedatives, and opioids increase the risk of orthostatic hypotension and, as a result, may increase the risks of accidents, fainting, and falls
Stimulants (such as Adderall) increase blood pressure and so can decrease hydrochlorothiazide’s effectiveness at lowering blood pressure.
Marplan (isocarboxazid), an antidepressant in the monoamine oxidase inhibitor (MAOI) drug class, is never given with drugs that lower blood pressure because the combination could cause a dangerous drop in blood pressure. Other drugs in the MAOI class can have the same effect and should not be taken with hydrochlorothiazide.

Foods and drinks to avoid when taking hydrochlorothiazide include alcohol, excessive amounts of caffeine, and diuretic herbs like dandelion, hibiscus, or green tea.

How to avoid hydrochlorothiazide side effects

Diuretics like hydrochlorothiazide often involve unwanted adverse effects, but they are important tools in fighting high blood pressure. A few guidelines can help both to minimize side effects and maximize the drug’s benefits.

1. Take hydrochlorothiazide as directed

Understand and follow all the directions given by the prescriber or printed on the prescription label. The standard dose is 12.5–50 mg per day for hypertension and 25–100 mg daily for edema. Generally, it is best to take hydrochlorothiazide in the morning. This is because it makes you urinate, and taking it at night would disrupt your sleep.

What if you miss a dose of hydrochlorothiazide? If a dose is missed, take it when remembered. However, if it’s almost time for the next dose, skip the missed dose. Take the next scheduled dose at the regular time. Do not double up on doses to try to make up for a missed dose.

2. Give the prescriber a complete medical history

The most worrisome side effects involve worsening existing medical conditions, so make sure the prescribing healthcare provider has an entire medical history, especially:

Kidney disease
Liver disease
Gout
Diabetes
Low potassium
High calcium
Narrow angles in the eyes or a history of glaucoma
Seizure disorders
Heart rate problems
Any upcoming parathyroid tests
Pregnancy or breastfeeding

3. Give the prescriber a list of all drugs being taken

Drug interactions are another major source of side effects, so make sure the prescribing healthcare provider has a complete picture of the prescription drugs, over-the-counter medications, and vitamins or dietary supplements being taken, particularly:

Blood pressure medications
Corticosteroids
Bile resins such as cholestyramine or colestipol
Lithium
NSAIDs

4. Do not miss follow-up appointments or tests

Staying safe on diuretics may require follow-up visits and tests. In this way, side effects can be corrected before they become hazardous.

5. Drink plenty of fluids

To avoid dehydration, drink plenty of clear fluids throughout the day. Avoid going outside if it’s hot. If hydrochlorothiazide is being used to treat fluid retention, follow the fluid restrictions given by the prescribing healthcare provider.

6. Avoid laxatives

Laxatives can cause dehydration. The risk is even greater when taking diuretics. The best advice is not to use laxatives casually when taking diuretics. If constipation is a problem, get medical advice about the most suitable treatment.

7. Skip the calcium supplements

Hydrochlorothiazide can increase calcium levels in the body. If taking calcium or vitamin D supplements, talk to the prescriber about continuing those supplements.

8. Avoid taking a late dose

Hydrochlorothiazide can be taken at any time of day, but if taken late, it could interfere with sleep by requiring frequent trips to the bathroom. Most people prefer to take hydrochlorothiazide in the morning.

9. Use sunblock

Hydrochlorothiazide increases the risk of developing non-melanoma skin cancer. That risk approximately triples for people with white skin. Avoid the sun. If it’s unavoidable, use high SPF sunscreen, and reapply frequently, especially if you are swimming and/or sweating.

How to treat side effects of hydrochlorothiazide

Not all hydrochlorothiazide side effects are avoidable. They are manageable, though. Some can be managed at home, but others may require a healthcare professional.

Dizziness

When standing up, stand up slowly and carefully. If standing up brings on an attack of dizziness or lightheadedness, sit down immediately. The primary goal is to avoid injuries brought on by a fall. Once the spinning or lightheadedness has stopped, then stand up slowly to prevent a relapse. Report symptoms of dizziness to your healthcare provider.

Dehydration

If any sign of dehydration is noticed, immediately drink clear fluids such as water or sports drinks. Contact a healthcare provider for medical advice. An extreme case of dehydration may require a visit to the emergency room. The symptoms of dehydration include:

Thirst
Dry mouth
Dry eyes
Urinating less than four times per day
Dark and strong-smelling urine
Dry skin
Dizziness
Drowsiness
Tiredness
Irregular or racing heartbeat

Electrolyte imbalances

Electrolyte imbalances, including potassium depletion, can quickly develop into a serious medical condition, so call a healthcare professional for medical advice if any of the symptoms of electrolyte imbalance are noticed:

Increased thirst
Weakness
Low energy
Muscle cramps or muscle pain
Constipation
Confusion
Abnormal or fast heartbeats
Tingling

Eye problems

Get immediate emergency medical treatment if eye pain, vision changes, “halos,” or blurred vision are experienced when taking hydrochlorothiazide. These could be symptoms of a form of glaucoma that progresses very rapidly.

Allergic reactions

A skin or allergic reaction to hydrochlorothiazide or any other drug can be very serious. Stop taking the drug and get emergency medical care at any sign of a severe skin or allergic reaction:

Wheezing
Shortness of breath
Trouble breathing
Swelling of the face, lips, tongue, or throat
Hives
Red or purple rash
Blistering or peeling skin
Skin pain
Fever
Sore throat
Eye pain and burning

Sources

Drug-induced alopecia. A review of the literature, Therapie
Drug-induced hair loss and hair growth. Incidence, management and avoidance, Drug Safety
Hydrochlorothiazide, Epocrates
Hydrochlorothiazide capsule prescribing information, U.S. National Library of Medicine
Hydrochlorothiazide drug summary, Prescriber’s Digital Reference