The short answer
L-arginine lowered blood pressure in one small hypertension subgroup, but extra low-blood-pressure risk with terazosin has not been demonstrated. Review the dose and symptoms before adding it.
What this answer covers
Oral terazosin and supplemental L-arginine; oral gram-dose studies, not IV arginine or dietary protein.
- Supplement or preparation
- L-Arginine
- Medication ingredient
- terazosin
What oral studies show
In a four-week study, significant BP lowering occurred only in the hypertensive subgroup receiving 12 g daily. A report of 19 healthy participants found no significant BP reduction at 6 or 12 g daily. The healthy participants may overlap the companion study, so these are not independent confirmations.
What remains unknown
Neither report establishes the effect of combining L-arginine with terazosin, whether symptomatic low pressure becomes more frequent, or a safe supplement dose for that combination. An average reduction in a hypertension study is different from harmful fainting in an individual.
Plan use around your clinical needs
Tell the prescriber the daily gram amount, reason for taking it and other ingredients. The studied amounts are not dosing recommendations. Do not reduce terazosin or rely on a spacing interval from these trials; treatment decisions should use your pressure readings and symptoms.
Respond to symptoms
Terazosin can cause dizziness, lightheadedness or fainting, particularly when treatment begins or the dose changes. Report troublesome symptoms to the prescriber; sit or lie down if you feel faint and avoid hazardous activity while affected. A blood-pressure reading and the timing of symptoms can help distinguish a medication effect from an unproven supplement interaction. The label also cautions about restarting after a treatment interruption; ask the prescriber how to restart.
Evidence and practical considerations
Side effects & toxicity
Oral L-arginine BP findings are dose- and population-dependent and do not prove excess hypotension with terazosin.
- Exact scope
- Oral terazosin and supplemental L-arginine; oral gram-dose studies, not IV arginine or dietary protein. with Current RxNorm confirms terazosin RxCUI 37798 IN. Oral hydrochloride capsules provide equivalent terazosin 1, 2, 5 or 10 mg.
- Medication form and route
- Oral
What remains uncertain
- Abstract-only oral studies; no exact combination, clinical hypotension or validated timing data.
Factors that may matter: Exact preparation and dose; Blood pressure and symptoms; Treatment initiation or dose change; Other medicines.
Read the supporting source summaries
Source 1: Current prescribing information
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients prescribed terazosin hydrochloride capsules.
First-dose and postural hypotension/syncope; caution after dose escalation or restarting interrupted therapy.
How this applies: Exact ingredient through the stated labeled salt and oral formulation. Current RxNorm confirms terazosin RxCUI 37798 IN. Oral hydrochloride capsules provide equivalent terazosin 1, 2, 5 or 10 mg.
No automatic transfer of another alpha blocker’s doses or timing; exact label used.
Source 2: Original clinical research
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 54 completing participants, including 35 with mild hypertension and 19 healthy controls.
Significant ambulatory BP reduction only in the 12 g/day hypertensive subgroup.
How this applies: Exact preparation and endpoint boundaries retained; this is not a measured terazosin combination unless explicitly stated.
Abstract-only; no terazosin co-use or demonstrated symptomatic hypotension. Not a recommended dose.
Source 3: Original clinical research
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 19 healthy adults.
BP decreases were not statistically significant.
How this applies: Exact preparation and endpoint boundaries retained; this is not a measured terazosin combination unless explicitly stated.
Abstract-only; healthy population. May overlap the healthy cohort of the companion study, so not counted as independent replication.
Source 4: Medication terminology
rxnav.nlm.nih.gov · Source check Sep 10, 2026
Population: Terminology.
terazosin is IN.
How this applies: Exact ingredient.
Not clinical evidence.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Sources checked and article drafted. | |
| Research summary published |
Article revision: 9a15215d1e711010
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.