Hydroflumethiazide and Lisinopril: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Hydroflumethiazide
No brand names on recordLisinopril
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
Both of your medicines lower blood pressure, just in different ways. Hydroflumethiazide is a water pill (diuretic) that makes you lose fluid and salt, and lisinopril relaxes your blood vessels. When these are combined, especially when the lisinopril is first started, your blood pressure can drop more than expected.
You might feel dizzy or lightheaded, particularly when standing up quickly. The good news is this effect is usually temporary and settles as your body adjusts. Your care team knows how to handle this by adjusting doses and watching your blood pressure. If you feel faint, sit or lie down and let your pharmacist or doctor know.
Effect: Additive/excessive BP reduction (risk of first-dose and postural hypotension) when an ACE inhibitor is added to diuretic therapy.
- Mechanism: Lisinopril-induced vasodilation combined with thiazide-mediated volume/sodium depletion; neither agent requires activation for this PD interaction.
- Direction: Enhanced hypotensive response, most pronounced at ACE inhibitor initiation in volume-depleted patients.
- Onset: Rapid; typically transient.
- Evidence: Theoretical/pharmacodynamic.
- Management: Consider reducing or holding the diuretic, or liberalizing salt intake, before starting lisinopril; if not feasible, use a reduced ACE inhibitor starting dose. Monitor BP and orthostatic symptoms.
What happens
Reduction of blood pressure
Interaction Deep Dive
When an ACE inhibitor is started in a patient already receiving diuretics, blood pressure can fall to an excessive degree3. Cases of severe postural hypotension have been documented after ACE inhibitors are combined with diuretic treatment. This effect appears more frequently with loop diuretics, though hypotension after the initial dose is common in individuals who are sodium depleted or hypovolemic as a result of diuretics or restricted sodium intake. Typically, this drop in blood pressure is transient6271. The likelihood of hypotensive reactions can be lessened by reducing or stopping the diuretic, or by raising salt consumption, prior to beginning ACE inhibitor therapy. When such steps cannot be taken, the initial dose of the ACE inhibitor should be lowered3.
Why it happens (mechanism)
Vasodilation and relative intravascular volume depletion
How to manage this interaction
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. This combination is common and manageable.
- Your team may lower or briefly pause the water pill, adjust your salt intake, or start lisinopril at a lower dose to ease you into it.
- They may check your blood pressure more closely, especially in the first days.
- Stand up slowly to avoid dizziness, and stay hydrated as advised.
Tell your pharmacist or doctor if you feel faint, very dizzy, or lightheaded when standing. These doses can be tailored and monitored to fit you.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) In a randomized crossover study (N=19) evaluating combined hydrochlorothiazide and enalapril use in older patients (62 to 84 years), the pharmacokinetics of enalapril were relatively unchanged by hydrochlorothiazide, but there was a significant rise in AUC (0 to 24 hours) along with a significant decrease in the renal clearance of enalaprilat 4.
b) Combined administration of perindopril and hydrochlorothiazide has been reported to cause a small decrease in peak serum concentrations of perindoprilat, together with a reduction in the proportion of the perindopril dose excreted as perindoprilat in the urine 5.
Common questions
Can I take Hydroflumethiazide and Lisinopril together?
Combining hydroflumethiazide with lisinopril can drop your blood pressure more than either alone, especially when lisinopril is first started, so watch for dizziness and let your care team adjust and monitor as needed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Hydroflumethiazide and Lisinopril interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How is the Hydroflumethiazide and Lisinopril interaction managed?
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. This combination is common and manageable. Your team may lower or briefly pause the water pill, adjust your salt intake, or start lisinopril at a lower dose to ease you into it. They may check your blood pressure more closely, especially in the first days. Stand up slowly to avoid dizziness, and stay hydrat… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Hydroflumethiazide or Lisinopril need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (7)
- Vlasses PH, Ferguson RK, & Chatterjee K: Captopril: clinical pharmacology and benefit-to-risk ratio in hypertension and congestive heart failure. Pharmacotherapy 1982; 2:1-17. PubMed
- Gluck Z, Beretta-Piccoli C, & Reubi FC: Long-term effects of captopril on renal function in hypertensive patients. Eur J Clin Pharmacol 1984; 26:315-323. PubMed
- Product Information: QBRELIS(TM) oral solution, lisinopril oral solution. Silvergate Pharmaceuticals (per manufacturer), Greenwood Village, CO, 2016. DailyMed
- Weisser K, Schloos J, Jakob S, et al: The influence of hydrochlorothiazide on the pharmacokinetics of enalapril in elderly patients. Eur J Clin Pharmacol 1992; 43:173-177. PubMed
- Todd PA & Fitton A: Perindopril: a review of its pharmacological properties and therapeutic use in cardiovascular disorders. Drugs 1991; 42:90-114.
- Atkinson AB, Brown JJ, Morton JJ, et al: Captopril in a hyponatremic hypertensive; need for caution initiating therapy (letter). Lancet 1979; 1:557-558.
- Pandhi P, Mondal S, Sharma BK, et al: Low dose captopril alone and in combination with hydrochlorothiazide in treatment of mild to moderate essential hypertension. Int J Clin Pharmacol Ther Toxicol 1986; 24:294-297.
Keep reading about Hydroflumethiazide
Keep reading about Lisinopril
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