8 Chlorthalidone Side Effects You Should Know About

Chlorthalidone is a thiazide-like diuretic medication. Diuretics (water pills) like chlorthalidone help your kidneys remove salt and water from the body. This can help lower your blood pressure if you have hypertension (high blood pressure). And it can also reduce edema (fluid buildup) from medical conditions like heart failure.

If you have a chlorthalidone prescription, you should know about possible side effects. Even though these side effects won’t happen to everyone, it’s important to know what to watch out for. Some are mild, but more common. And others are rare, but more severe.

Below, we’ll detail eight l side effects you should know about. But keep in mind, this isn't a complete list. Talk to your healthcare provider about all risks and benefits associated with chlorthalidone.

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1. Increased urination

One of the most common effects of chlorthalidone is making you pee more. You should expect more frequent trips to the bathroom when taking chlorthalidone. This is just the medication doing what it’s supposed to. 

You’ll usually start having to pee more within 2 to 3 hours of taking chlorthalidone. It’s a good idea to take chlorthalidone in the morning so you can avoid having to pee frequently overnight.  

2. Dizziness

Because chlorthalidone lowers blood pressure, it can also cause dizziness. Dizziness usually happens when your blood pressure gets too low. This can happen if your chlorthalidone dose is too high. It’s also more likely in the first few days after starting chlorthalidone (or with a dose increase). And it's more likely to happen if you drink alcohol.

Chlorthalidone may cause a sudden drop in blood pressure when changing positions. This is called orthostatic hypotension. Symptoms include dizziness and feeling like you may pass out. 

Change positions slowly if you experience orthostatic hypotension. If symptoms continue or worsen, talk to your healthcare provider. They may recommend a lower dose of chlorthalidone. Or they may switch you to a different medication.

3. Headache

People taking chlorthalidone may experience headaches. This is usually more common when you first start the medication. This side effect usually improves over time as your body gets used to chlorthalidone.

If headaches continue or get worse, make sure to let your healthcare provider know. It could be a sign that something else is going on, like electrolyte abnormalities (more on that below). 

In severe cases, intense headaches can be a warning sign of hypertensive emergency. This is a medical emergency where blood pressure is dangerously high. It requires immediate medical attention.

4. Sun sensitivity

People taking chlorthalidone may become more sensitive to the sun. This is known as photosensitivity, which can lead to a higher chance of sunburn or rashes.

Not everyone who takes chlorthalidone will experience photosensitivity. But everyone taking chlorthalidone should follow a few tips for minimizing sun exposure:

• Avoid direct sun exposure when possible.

• Stay away from tanning beds.

• Apply sunscreen with an SPF 30 or higher to provide protection from the sun.

• Wear protective clothing like long sleeves, pants, and a hat when you can.

If you get a sunburn, drink water to stay hydrated and apply a cool compress to the affected area. You can also try topical aloe vera gel to help relieve irritation. 

Talk to your healthcare provider about whether over-the-counter pain medications can help. Medications like ibuprofen (Advil, Motrin) can help relieve pain and inflammation. But they aren’t always recommended in people with high blood pressure. This is especially true if you have existing kidney problems.

If you do get a severe sunburn while taking chlorthalidone, let your provider know. Symptoms of a severe burn include fever, chills, or blistering skin.

5. Electrolyte abnormalities

People taking thiazide diuretics may experience electrolyte abnormalities. Possible electrolyte issues include:

• Low potassium (hypokalemia)

• Low sodium (hyponatremia)

• Low magnesium (hypomagnesemia)

• Low chloride (hypochloremia)

• High calcium levels (hypercalcemia) 

People taking chlorthalidone should watch for signs and symptoms of electrolyte abnormalities. For example, symptoms of hypokalemia and hypomagnesemia include muscle weakness or twitching. And hyponatremia can cause symptoms like extreme fatigue or confusion. It can also cause severe complications, including seizures. 

For most people, electrolyte abnormalities are usually minor. Your healthcare provider will closely monitor your electrolytes while you are taking chlorthalidone. In some cases, your healthcare provider may prescribe electrolyte supplements like potassium chloride (Klor-Con).

6. High blood sugar

People taking thiazide diuretics may experience high blood sugar. It’s not exactly clear how this happens. But some researchers believe that chlorthalidone may worsen insulin resistance. Insulin resistance is when your body doesn’t respond normally to insulin. Blood sugar can rise as a result.

Despite this risk, it’s important to treat hypertension if you have it. This is especially true for people with diabetes. If you’re taking chlorthalidone, your healthcare provider may monitor your blood sugars. If you have diabetes, you’re also likely monitoring your blood sugar levels at home. It’s important to do this as often as your healthcare provider tells you to. You should also know the symptoms of hyperglycemia, including:

• Dry mouth 

• Feeling thirstier than usual

• Peeing more often

• Headache

• Blurry vision

• Nausea or vomiting

• Fruity smelling breath

If you feel any of these symptoms, contact your healthcare provider. And if they feel severe, seek medical attention.

7. Higher risk of gout attacks

Gout is a type of arthritis (joint inflammation). It's caused by a buildup of uric acid crystals. People taking chlorthalidone may be at higher risk for gout attacks. This is because chlorthalidone can increase uric acid levels.

The risk of gout attacks usually only applies to people with preexisting gout. It’s uncommon for chlorthalidone to cause gout in people who don’t already have it.

The American College of Rheumatology recommends that people with gout try to avoid hydrochlorothiazide (Microzide) if possible. Hydrochlorothiazide is a common thiazide medication. They don’t make a specific recommendation for chlorthalidone. But it may be wise to avoid chlorthalidone too.

If you have gout, talk to your healthcare provider about the risks and benefits of chlorthalidone. And if you experience any symptoms of gout, let your healthcare provider know. This includes pain, swelling, or redness in your joints. They may recommend another blood pressure medication instead of chlorthalidone. 

If chlorthalidone is necessary, they may recommend a medication to treat gout attacks. Examples include colchicine, indomethacin, or naproxen (Aleve, Naprosyn).

8. Kidney problems

Chlorthalidone causes the kidneys to work harder to remove extra fluids. In some cases, this can damage the kidneys and lead to kidney problems. People with existing chronic kidney disease are at higher risk for these complications.

Some research suggests chlorthalidone is more likely than hydrochlorothiazide to cause kidney problems. But we need more studies comparing these two medications to find out how significant this is.

If you take chlorthalidone, your healthcare provider will monitor your kidney function with lab tests. You should also make sure to drink enough water. Dehydration can make kidney problems worse.

9. Allergic reactions in people with sulfa allergies

A sulfa allergy is an allergic reaction to medications that contain the chemical sulfonamide. Sulfonamide antibiotics are one of the most common causes of medication-related allergic reactions. Examples include Bactrim (trimethoprim/sulfamethoxazole). However, chlorthalidone also contains sulfonamide. 

Common symptoms of a sulfa allergy include hives or a red rash with flat and raised areas. In rare cases, severe allergies can occur. This includes life-threatening skin reactions like Stevens-Johnson syndrome and toxic epidermal necrolysis. Anaphylaxis may also occur. This is a severe allergic reaction that can cause difficulty breathing. These serious allergic reactions require immediate medical care.

Experts aren't sure if an allergic reaction to sulfonamide antibiotics means you'll be allergic to chlorthalidone. Still, let your healthcare provider know if you have a sulfa allergy. They can help decide if you should avoid chlorthalidone entirely. They may recommend a different diuretic instead.

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Written by:

Kevin Le, PharmD, BCPS, BCPPS

Kevin Le, PharmD, BCPS, BCPPS is a clinical pharmacy specialist in solid organ transplant at Ann & Robert H. Lurie Children’s Hospital of Chicago. He has been working as a pediatric pharmacist since 2016.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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