Researchers tested a common blood pressure medication called hydrochlorothiazide to see if it could help people with hypoparathyroidism, a condition where the body doesn’t make enough parathyroid hormone and has trouble keeping calcium levels normal. In a carefully controlled study with 26 adults, the medication combined with a low-salt diet safely raised calcium levels in the blood after just 5 days. The treatment also reduced the amount of calcium lost in urine, which is important because people with this condition often lose too much calcium. The medication was well-tolerated with no serious side effects, suggesting it could be a helpful and affordable addition to current treatments.

The Quick Take

  • What they studied: Whether a water pill called hydrochlorothiazide could safely help raise calcium levels in people with hypoparathyroidism (a condition where the parathyroid glands don’t work properly)
  • Who participated: 26 adults with hypoparathyroidism who weren’t candidates for surgery. They were already taking calcium and vitamin D supplements and following a low-salt diet
  • Key finding: After taking the medication for 5-8 days, participants’ blood calcium levels increased from 8.61 to about 9.0-9.04 mg/dL (a statistically significant improvement, p<0.001), and they lost less calcium in their urine
  • What it means for you: This medication may offer a new, affordable treatment option for people struggling to maintain healthy calcium levels despite taking standard treatments. However, this is early-stage research with a small group, so more testing is needed before it becomes standard care

The Research Details

This was a carefully controlled experiment where 26 adults with hypoparathyroidism received either the medication or a placebo (fake pill) for 7 days. After a 15-day break to let the medication leave their bodies, they switched groups so everyone got to try both the real medication and the placebo. This crossover design is powerful because each person serves as their own comparison. All participants were already stable on calcium supplements and vitamin D, and everyone followed a low-salt diet. The researchers measured blood calcium, urine calcium, and other markers of bone health at multiple time points.

The crossover design is particularly valuable here because hypoparathyroidism varies between individuals. By having each person try both the medication and placebo, researchers could see the true effect of the drug while controlling for individual differences. The short 7-day treatment period allowed researchers to assess quick effects while minimizing risk. The inclusion of a washout period ensures the medication completely left participants’ bodies before they switched treatments.

This study has several strengths: it’s randomized (reducing bias), placebo-controlled (showing the medication works better than fake treatment), and uses a crossover design (powerful for small groups). However, the study is small (26 people) and only lasted 7 days for the main phase, so we don’t know about long-term effects. It was single-blinded, meaning participants knew which treatment they were getting, which could introduce some bias. The study was conducted at a single center, so results may not apply to all populations

What the Results Show

The main finding was that hydrochlorothiazide significantly increased blood calcium levels. At baseline, participants had an average blood calcium of 8.61 mg/dL. After 5 days on the medication, this rose to 9.01 mg/dL, and by day 8 it was 9.04 mg/dL. These increases were statistically significant (p<0.001), meaning they’re very unlikely to have happened by chance. Importantly, calcium levels remained within the normal healthy range, so no one became over-supplemented. When participants took the placebo instead, calcium levels didn’t increase, confirming the medication was responsible for the improvement. During the optional 4-week extension phase where everyone took the real medication, calcium levels continued to rise while urine calcium loss decreased significantly.

The medication also reduced how much calcium was lost in urine, which is crucial for people with hypoparathyroidism who already struggle with excessive calcium loss. Kidney function remained stable throughout the study, and potassium levels didn’t drop dangerously (hypokalemia), which is a known risk with water pills. Bone turnover markers (β-CTX and P1NP) showed expected changes. Parathyroid hormone levels remained stable, indicating the medication didn’t interfere with the body’s natural regulatory mechanisms. No adverse effects were reported during the extension phase

Hypoparathyroidism is typically managed with calcium supplements and active vitamin D (calcitriol), which is what all participants were already taking. This study suggests hydrochlorothiazide could be added to this standard approach to improve calcium control. The medication works through a different mechanism—it reduces calcium loss through the kidneys—rather than increasing calcium absorption. This is a novel application of an old, inexpensive medication, which could be particularly valuable in resource-limited settings

The study involved only 26 people, which is a small number, so results may not apply to everyone with this condition. The main treatment phase lasted only 7 days, so we don’t know if benefits continue or if tolerance develops over months or years. The study was single-blinded (participants knew which treatment they were getting), which could introduce psychological effects. It was conducted at one center in one country, so results may differ in other populations. The study excluded people with autoimmune hypoparathyroidism and syndromic forms, so findings may not apply to those groups. Long-term safety and optimal dosing weren’t fully explored

The Bottom Line

Based on this early research, hydrochlorothiazide combined with a low-salt diet appears to be a safe and potentially effective addition to standard calcium and vitamin D therapy for nonsurgical hypoparathyroidism. However, this is preliminary evidence from a small, short-term study. The recommendation confidence level is MODERATE—the results are promising but need confirmation in larger, longer studies before becoming standard practice. Anyone with hypoparathyroidism interested in this treatment should discuss it with their endocrinologist, as individual circumstances vary

This research is most relevant to adults with nonsurgical hypoparathyroidism who struggle to maintain normal calcium levels despite taking standard treatments. It may be particularly valuable for people in countries where expensive medications are less accessible, since hydrochlorothiazide is inexpensive and widely available. People with autoimmune hypoparathyroidism or syndromic forms weren’t studied, so applicability is unclear for these groups. Those with kidney disease, heart problems, or electrolyte imbalances should be cautious and consult their doctor

In this study, calcium levels began rising within 5 days of starting the medication. However, this short-term study doesn’t tell us how long benefits last or whether the body adapts over time. Realistic expectations based on this research: you might see improvements in calcium levels within a week, but long-term benefits (weeks to months) remain unknown. Most people would need ongoing monitoring to ensure the treatment continues working and remains safe

Want to Apply This Research?

  • Track weekly blood calcium levels (if testing is available) and daily symptoms like muscle cramps, tingling, or fatigue. Also monitor salt intake to ensure you’re staying on the low-sodium diet, as this is crucial for the medication to work effectively
  • If prescribed this medication, users should: (1) take it consistently at the same time daily, (2) maintain strict low-sodium diet compliance by logging meals and checking sodium content, (3) stay hydrated, and (4) report any new symptoms like weakness, irregular heartbeat, or excessive thirst to their doctor
  • Set up a monthly reminder to log blood test results (calcium, potassium, kidney function). Track any symptoms in a daily journal. Create alerts for medication refills. Share trends with your healthcare provider during regular check-ins to ensure the treatment remains safe and effective

This research describes a promising new treatment approach for hypoparathyroidism, but it is based on a small, short-term study and should not be considered definitive medical guidance. Hydrochlorothiazide is a prescription medication that carries potential risks and requires medical supervision. Do not start, stop, or change any medication without consulting your doctor. This information is for educational purposes only and does not replace professional medical advice. People with hypoparathyroidism should work closely with an endocrinologist before considering this treatment, as individual circumstances, other medications, and medical history significantly affect safety and effectiveness. Long-term effects remain unknown.