Lisinopril and Polythiazide: 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
Polythiazide
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 these medicines lower your blood pressure, but in different ways. Polythiazide is a water pill that makes your body get rid of extra fluid and salt. Lisinopril relaxes and widens your blood vessels. When you start lisinopril while already taking a water pill, your blood pressure can drop more than expected, especially with the very first dose.
You might feel dizzy or lightheaded, particularly when standing up quickly. The good news is this is usually temporary, and your care team knows how to handle it. They may adjust your doses or watch you closely at the start. If you feel faint, sit or lie down and call your pharmacist or doctor.
Effect: Additive antihypertensive effect with risk of excessive BP reduction, including first-dose and postural hypotension.
Mechanism: Thiazide-induced volume/sodium depletion combined with ACE inhibitor vasodilation. Neither agent is enzymatically activated in a way that alters direction; this is a pharmacodynamic (PD) interaction, not PK.
- Direction: Increased hypotensive response (rapid onset, often transient)
- Evidence: Theoretical, but clinically well recognized with diuretic plus ACEi combinations
- Management: Before initiating lisinopril, reduce or hold the diuretic or liberalize salt intake if appropriate; if not feasible, use a low lisinopril starting dose. Monitor BP, orthostatic symptoms, renal function, and electrolytes.
What happens
Reduction of blood pressure
Interaction Deep Dive
When an ACE inhibitor is started in patients already receiving diuretics, blood pressure may fall to an excessive degree3. The addition of ACE inhibitors to diuretic regimens has been associated with reports of severe postural hypotension. This occurrence has been noted more frequently with loop diuretics, yet first dose hypotension is frequent among patients who are sodium depleted or hypovolemic as a result of diuretics or restricted sodium intake. Typically, this hypotensive reaction is transient6271. To reduce the likelihood of hypotensive effects, the diuretic can be lowered or stopped, or salt intake can be raised, before ACE inhibitor therapy begins. 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
This combination is used intentionally and safely all the time, but the start of therapy is the key moment to watch.
- Keep taking both medicines as prescribed unless your prescriber tells you otherwise.
- When lisinopril is first started, your team may lower or briefly pause the water pill, or have you loosen salt restriction, to lessen the drop in blood pressure.
- If those steps are not possible, they may simply begin lisinopril at a lower dose and increase it gradually.
- Your care team may check your blood pressure more closely early on.
Rise slowly from sitting or lying down, and tell your pharmacist or doctor if you feel dizzy, lightheaded, or faint.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) In a randomized crossover trial (N=19) evaluating combined hydrochlorothiazide and enalapril use in older patients (62 to 84 years), the pharmacokinetics of enalapril were relatively unaffected by hydrochlorothiazide, however there was a significant rise in AUC (0 to 24 hours) together with a significant decrease in the renal clearance of enalaprilat 4.
b) A slight decline in peak serum concentrations of perindoprilat, along with a reduction in the proportion of the perindopril dose eliminated as perindoprilat in the urine, has been reported when perindopril and hydrochlorothiazide are administered together 5.
Common questions
Can I take Lisinopril and Polythiazide together?
Starting lisinopril while on the water pill polythiazide can cause an extra drop in blood pressure, especially at first, so expect closer monitoring and possible dose tweaks early on. Rise slowly and report any dizziness or fainting to your care team. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Lisinopril and Polythiazide 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 Lisinopril and Polythiazide interaction managed?
This combination is used intentionally and safely all the time, but the start of therapy is the key moment to watch. Keep taking both medicines as prescribed unless your prescriber tells you otherwise. When lisinopril is first started, your team may lower or briefly pause the water pill, or have you loosen salt restriction, to lessen the drop in blood pressure. If those steps are not possible, the… 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 Lisinopril or Polythiazide 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 Polythiazide
Keep reading about Lisinopril
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist