Older woman taking blood pressure

Hydrochlorothiazide (HCTZ, HCT) is a diuretic (water pill) that is widely prescribed to lower blood pressure. Roughly 50 million prescriptions were written for this “thiazide” diuretic last year. That does not count the millions of prescriptions that were filled for other medications that contain HCT along with another drug to control hypertension. A few examples include lisinopril plus HCT, valsartan plus HCT and metoprolol plus HCT. One side effect that is rarely discussed with patients who take hydrochlorothiazide is dangerously low sodium levels. This reader’s mother had a close call:

Diuretics That Lower Sodium and Potassium:

Q. My elderly mother has been very conscientious about a low-salt diet. She never salts her food and is careful not to eat processed foods high in sodium.

Despite this, her doctor diagnosed her with mild high blood pressure and put her on a diuretic called hydrochlorothiazide. Last week she got up in the middle of the night to go to the bathroom. She suddenly felt weak and collapsed. When the paramedics came in response to her call button, she was confused.

They took her to the hospital and discovered that her sodium and potassium levels were perilously low. Could her medicine be responsible for this scary episode?

Dangerously Low Sodium & Potassium Levels:

A. Hydrochlorothiazide (HCTZ, HCT) is one of the most commonly prescribed blood pressure drugs in the world. It is considered safe and cost effective.

Nonetheless, HCTZ could have led to your mother’s low sodium and potassium levels. This medication can cause loss of these crucial electrolytes (Journal of Emergency Medicine, March, 2015).

One population-based study found that those taking this diuretic were five times more likely to develop hyponatremia (low sodium) than those not on it (American Journal of Kidney Diseases, July 2013).

Symptoms of Hyponatremia:

Dangerously low sodium levels can cause nonspecific symptoms. That means it can be hard to diagnose this condition without a blood test. Weakness and confusion are common symptoms of low sodium. Others include loss of appetite, muscle cramps, headache and nausea. If the sodium depletion is severe, seizures or coma may result.

Symptoms of Hypokalemia (low potassium):

Some symptoms of low potassium levels are similar to low sodium levels. Weakness and confusion are red flags. Other symptoms to be alert for include muscle cramps or spasms, numbness or tingling, palpitations or irregular heart rhythms, constipation, thirst, frequent urination or muscle paralysis.

Stories from Readers:

Liz in Raleigh, NC, had a close call:

“BEWARE IF YOU TAKE DIURETICS. On October 29, 2014, I was in my neighbor’s yard around dusk to check on his cat. I fell on something and hit my head, ending up in the trauma intensive care unit for four days. I needed four staples in my head to close the cut.

“I had limited memory before I fell and no memory at all for about three days while in the hospital. The diagnosis: low sodium. Mine was 116. The normal range is 136-145. I had no noticeable signs before I fell that anything was wrong.”

Hyponatremia is diagnosed when sodium levels fall below 135 mEq/L.

Marlene in Florida responded to Liz:

“I almost died two years ago when I had hyponatremia (low sodium in the blood), caused by diuretics prescribed by a new-to-me cardiologist. I had avoided a lot of salt for years. That wasn’t what caused the hyponatremia. It was the diuretics.

“I, like you, suffered memory loss.”

The People’s Pharmacy Perspective:

Many people can take hydrochlorothiazide without experiencing either dangerously low sodium or potassium levels. But we encourage people who are following a low-sodium diet and are taking diuretics to 1) have their blood tested periodically for both sodium and potassium and 2) be alert for symptoms of dangerously low sodium or potassium levels. When in doubt, contact a physician immediately and be tested promptly.

You can learn more about HCTZ side effects here.

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  1. Polly

    My primary care doctor put me on HCTZ after observing my BP slowly increasing over the years. I was delighted, no, thrilled, that one of the results of being on HCTZ was no more migraine headaches. The dr said this was an “off lable” response. I didn’t care what it was, I was so grateful not to have anymore migraines, a hereditary curse.

    Unfortunately, after a period of time, I started having shortness of breath (S.O.B.) and some irregular heart palpitations that got so bad I was deeply concerned I may have the idiopathic pulmonary fibrosis that my mother and her brother had both died from.

    The dr felt that I needed more exercise. She didn’t do any blood work or chest X-ray, nothing, and she was the one who put me on HCTZ a couple of years earlier. I didn’t think that was the answer, do I went to a dr outside of my healthcare system, my husband’s cardiologist consultant. He had a blood test done when I went in for a catheterization procedure. And the blood test showed my potassium level was so low I was in a near-death situation. If my heart had stopped they wouldn’t have been able to start it.

    The catheterization showed I have the heart of a 20 year old ( I was in my late 60’s) and gave me a 5 hour IV of potassium to bring me back to healthy levels of potassium. The problem was the HCTZ. He took me off the HCTZ and put me on atenolol. Unfortunately, within three days I had migraines again. When my prescription of atenolol was nearly gone, I asked the cardiologist dr to put me back on HCTZ with a prescription potassium (for assurance that the potassium level in the prescription would be as stated) which he did. After starting that combination, no more migraines. And now, about four years later, still no migraines and no more S.O.B. I’ve been doing fine. And I have a new primary care Dr.

  2. JimC
    Orlando, FL

    I am 84 and taking CHLORTHALIDONE. How does this compare with hydrochlorothiazide in causing low Na & K.

    • john

      I (64-year-old) male also noticed that 12.5 mg hydrochlorothiazide for pre-hypertension or “elevated bp” completely eliminated my headaches, some of which were migraines.

      The question I have, however, is whether or not a diuretic should be prescribed for high bp where the patient has, often for years, been on a zero dietary salt?!

      If diuretics reduce bp by causing the body to excrete more salt, then what real use can the medication have where the patient consumes zero dietary salt diet anyway? Are the tiny amounts of salt in a no-salt diet still important to deal with? Do diuretics work EVEN where the patient has for years never consumed salt in any form? (EG, vegetarians who consume zero processed food)

  3. S.

    Just wondering, would it make sense to stop sodium restrictions and return to a more moderate use of salt along with use of hydrochlorothiazide? I’m not sure this would be the recommended approach, but regular testing for sodium and potassium seems like it would be expensive.

  4. Lee G

    In Nov 2011 (age 67) 9 days after starting on HCTZ my heartbeat became irregular. Immediately I stopped taking it but the irregularity continued. My GP Doc turned me over to a cardiologist who spent several months trying different drugs to correct the problem. I was given a MRI which showed no heart disease.

    After no success with drugs I was turned over to a cardiologist who specializes in electrophysiology (May 2012). The same month I had an Cardiac Ablation. 6 catheters are threaded in the groin arteries up to the heart and heat is used to burn tiny areas of the heart to correct the errant electrical pathways. Amazingly no overnight stay in the hospital is required.

    FYI: Now there is a treatment which uses very cold (Cryoballoon Ablation) to treat this and a friend had it last year with great results. Since my Ablation I occasionally have episodes of irregular heartbeat once a month but they only last around 5 minutes so no problem. I take no heart drugs and refuse to take diuretics, have some swelling in my feet but live with it.

  5. Art

    One of the symptoms of low sodium in the blood is insomnia . My wife is taking triam/htzt and her sodium in blood was always 132/133 a few notch below normal. She was following a low sodium diet , and her blood pressure specialist always advised her to drink less water. She was recently hospitalized due to too low sodium, and doctors in the hospital asked her why you drink too much water (which she did not), and nobody blamed water pill she was taking.

    After reading some recent she returned to normal / slightly above normal salt diet (doctors never advised that), her sodium is now 136/137 and her insomnia completely disappeared.

    Water pill HTZT and low sodium diet is very dangerous, especially in hot weather.

  6. Dorothy
    Laurel, Maryland

    I take, DAILY, 1- Losartan potassium – 50 mg, 1 – Amlodipine BESYLATE – 5 mg, and 1- Metformin HCL – 500 mg. I am also incontinent which has gotten worse as I get older. (Having had 3 c-sections as well as a ‘partial hysterectomy’, as well as a full hysterectomy many years ago I’m not too surprised about incontinence.)
    I am concerned about the metformin wondering about the worsening of the incontinence. I make no attempt to skip salt, but rarely use extra salt.

  7. Priscilla

    I have used HCTZ for several years; did have infrequent muscle spasms in the lower legs, frequent urination, bladder incontinence. Quite recently, suffered a fainting spell, with accompanying dizziness, shakiness. Am presently under a cardiologist’s care after three days of hospitalization. Doctor suspects HCTZ but haven’t decided on clear diagnosis.

  8. Curtis

    Also (and I didn’t learn this until a couple of years ago, incredibly enough) did you know that HCTZ and other thiazide diuretics are the BP meds most likely to cause erectile dysfunction? I had no clue, then when I started getting my guys off of it I made lots of new friends.

  9. Tony

    I took HCTZ for about 15 years to lower my High BP…
    Soon after I started taking it, I started getting episodes of Gout…
    Belatedly, I finally put the pieces together that HCTZ was a major contributor to my gout…
    Now I only take tart cherries to lower my chances of any gout
    and I also take L ‘Arginine to bring my HBP down into normal range…

  10. Shelly

    Hello. Okay my dilemma is this. The story about salt intake blah blah blah. Isn’t salt a necessary conduit to allow the body to pass along electrical messages to other bodily chemical responses. I’m no expert, just a holistic health coach that is tired of hearing the perils of salt intake.
    Salt is an age old medicinal vessel. It helps pass along toxins from the body when used as a medium to soak ones feet (Epsom salts).

    Along with the soak it gives our bodies a much needed boost of magnesium. Most salt intake is high because of the amount that is put in our foods this day and age.

    Not condoning the years of study about using salt in certain cases. I do however think if we use anything including salt and use a salt not enhanced with Iodine. It can be and is a very useful item to have in ones arsenal of personal health. We must be advocates for ourselves and not blindly follow what the is termed good for you by high paid lobbyists or advocates for the food industry.
    Be aware of everything you eat. We do not have the same food items our grandfathers and grandmothers had. Everything is money based as opposed to customer minded. Ive been an champion of healthy choices and better options for years. Just my 2 cents about the whole thing.

  11. ray

    Zero over zero is a nice low blood pressure!

    • nancy lynn jocoy
      South Carolina

      Ray, Epsom salts is Magnesium Sulfate and has nothing to do with sodium.

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