Trichlormethiazide 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
Trichlormethiazide
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, and together they can lower it more than either one alone. Trichlormethiazide is a water pill (a diuretic) that makes you lose fluid and salt. Lisinopril is an ACE inhibitor that relaxes your blood vessels. When you start lisinopril while already on the water pill, your blood pressure can drop quickly, especially with that very first dose.
You might feel dizzy or lightheaded, particularly when standing up. The good news is this effect is usually short-lived and very manageable. Your care team can adjust the timing or dose so you start safely. If you feel faint, sit or lie down and let your pharmacist or doctor know.
Effect: Additive/potentiated hypotension when an ACE inhibitor (lisinopril) is initiated in a patient already on a thiazide diuretic (trichlormethiazide). Neither is a prodrug requiring this consideration; the interaction is pharmacodynamic, not metabolic.
- Mechanism: ACE inhibitor vasodilation combined with diuretic-induced intravascular volume/sodium depletion.
- Direction: Enhanced blood-pressure lowering, i.e. first-dose and postural hypotension.
- Onset: Rapid; typically transient.
- Evidence: Theoretical, severity moderate.
Management: Before initiating lisinopril, consider reducing/holding the diuretic or liberalizing sodium; if not feasible, use a reduced ACE inhibitor starting dose. Monitor BP and orthostatic symptoms early in therapy.
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. Cases of severe postural hypotension have been documented when an ACE inhibitor is combined with existing diuretic therapy. This complication has been seen more frequently with loop diuretics, yet hypotension after the first dose occurs often 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 effects can be lessened by lowering or stopping the diuretic, or by raising salt intake, prior to beginning ACE inhibitor treatment. Where such steps cannot be undertaken, use a lower initial dose of the ACE inhibitor3.
Why it happens (mechanism)
Vasodilation and relative intravascular volume depletion
How to manage this interaction
Keep taking both medicines as prescribed unless your care team tells you otherwise. This effect is usually temporary and easy to manage.
- Your team may lower or briefly hold the water pill before starting lisinopril, or advise a bit more dietary salt, to soften the initial blood-pressure drop.
- If those steps are not possible, they may simply start lisinopril at a lower dose.
- Your dose may be adjusted and individualized, and your team may monitor your blood pressure more closely at the start.
- Stand up slowly, and tell your pharmacist or doctor if you feel dizzy, faint, or lightheaded.
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), simultaneous use of hydrochlorothiazide and enalapril in elderly patients (62 to 84 years) demonstrated that hydrochlorothiazide had relatively little effect on the pharmacokinetics of enalapril, but there was a significant rise in AUC (0 to 24 hours) and a significant decrease in the renal clearance of enalaprilat 4.
b) A slight decrease 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 given together 5.
Common questions
Can I take Trichlormethiazide and Lisinopril together?
Starting lisinopril while on the water pill trichlormethiazide can cause a quick, usually temporary drop in blood pressure, so watch for dizziness. Your care team can prevent problems by adjusting the diuretic, salt intake, or the lisinopril starting dose. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Trichlormethiazide 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 Trichlormethiazide and Lisinopril interaction managed?
Keep taking both medicines as prescribed unless your care team tells you otherwise. This effect is usually temporary and easy to manage. Your team may lower or briefly hold the water pill before starting lisinopril, or advise a bit more dietary salt, to soften the initial blood-pressure drop. If those steps are not possible, they may simply start lisinopril at a lower dose. Your dose may be adjust… 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 Trichlormethiazide 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 Trichlormethiazide
Keep reading about Lisinopril
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