Phenylephrine and Terazosin Interaction
Drug interaction information between Phenylephrine and Terazosin.
Phenylephrine and Terazosin have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Phenylephrine and Terazosin. Major interactions are generally avoided, moderate ones may need monitoring or a dose adjustment, and minor ones are usually low-risk. This page shows the documented mechanism and guidance. Label-documented interactions are not a complete safety review, so always confirm your own medications with a pharmacist or doctor. Educational information, not medical advice.
How They Interact
These drugs work against each other because one relaxes blood vessels to lower blood pressure while the other narrows them to raise it. This can make your blood pressure medicine less effective.
What To Do
Talk to your doctor before using these together, as your blood pressure may need to be checked more often. They may suggest a different decongestant that does not affect blood pressure.
FDA Label Information
Terazosin has been used concomitantly in at least 50 patients on the following drugs or drug classes: analgesic/anti-inflammatory (e.g., acetaminophen, aspirin, codeine, ibuprofen, indomethacin); antibiotics (e.g., erythromycin, trimethoprim and sulfamethoxazole); anticholinergic/sympathomimetics (e.g., phenylephrine hydrochloride, phenylpropanolamine hydrochloride, pseudoephedrine hydrochloride); antigout (e.g., allopurinol); antihistamines (e.g., chlorpheniramine); cardiovascular agents (e.g., atenolol, hydrochlorothiazide, methyclothiazide, propranolol); corticosteroids;...
Terazosin Also Interacts With
- Hydrochlorothiazide minor
- Ibuprofen minor
- Allopurinol minor
- Aspirin minor
- Atenolol minor
Frequently Asked Questions
Can I take Phenylephrine and Terazosin together?
This is a minor interaction. Talk to your doctor before using these together, as your blood pressure may need to be checked more often. They may suggest a different decongestant that does not affect blood pressure.
How serious is the interaction between Phenylephrine and Terazosin?
This interaction is classified as "minor" severity by the FDA. Minor interactions are unlikely to cause significant problems but should still be mentioned to your healthcare provider.
Why do Phenylephrine and Terazosin interact?
These drugs work against each other because one relaxes blood vessels to lower blood pressure while the other narrows them to raise it. This can make your blood pressure medicine less effective.
Understanding the Phenylephrine and Terazosin Interaction
FDA-approved prescribing information for these two drugs flags their combination as a minor-severity interaction. Phenylephrine belongs to the Alpha-1 Agonist class and Terazosin belongs to the Alpha-1 Blocker class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: These drugs work against each other because one relaxes blood vessels to lower blood pressure while the other narrows them to raise it. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.
Context around a specific patient determines real-world impact. Phenylephrine has 2 total documented interactions on file in this dataset, and Terazosin has 15. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: Talk to your doctor before using these together, as your blood pressure may need to be checked more often. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.
An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Phenylephrine or Terazosin based on a web page, speak with your prescriber or pharmacist before making any change.
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. Always consult your healthcare provider about drug interactions.
Read our methodology - how this data is sourced, computed, and verified.