Doxazosin and Tadalafil: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Tadalafil
Doxazosin
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.
What happens
Increased risk of hypotension
Interaction Deep Dive
The concomitant administration of tadalafil and doxazosin is not recommended1. Concomitant administration of tadalafil with doxazosin can result in additive blood pressure lowering effects and symptomatic hypotension 234. In drug-drug interaction studies, concomitant use of doxazosin and tadalafil was shown to augment the hypotensive effects of doxazosin 435. Monitor blood pressure and for symptoms of hypotension 2.
Why it happens (mechanism)
Additive hypotensive effects
Literature reports
3 reports — tap to read
a) In subjects receiving concomitant tadalafil as a 20 mg single dose and doxazosin 8 mg/day, the blood pressure-lowering effect of doxazosin was augmented by tadalafil. The hypotensive effect was still present at 12 hours following administration and had generally disappeared at 24 hours. The combination resulted in a greater number of subjects with potentially clinically significant hypotension. In an additional study in which subjects were given tadalafil at the same dose and doxazosin 4 and 8 mg/day, augmentation of low blood pressure appeared unrelated to dosing times and resulted in a greater number of outliers for the combination than had been observed in the previous study. In further study in which doxazosin up to 4 mg/day was added to tadalafil 5 mg/day, there was again an augmentation of hypotensive response 4.
b) The coadministration of tadalafil and doxazosin significantly increased the hypotensive effect of doxazosin, whereas the coadministration of tadalafil and tamsulosin had no such effect. Two randomized, double-blind, placebo-controlled, crossover studies, each conducted in 18 healthy men, evaluated the hemodynamic interaction between tadalafil and 2 alpha-adrenergic antagonists, doxazosin and tamsulosin. In the doxazosin protocol, subjects were given doxazosin 8 mg daily for a minimum of 7 consecutive days to achieve a steady state concentration before administration of a single dose of either tadalafil 20 mg or placebo administered simultaneously with doxazosin. In the tamsulosin protocol, subjects were given tamsulosin 0.4 mg daily for a minimum of 7 consecutive days to achieve a steady state concentration before administration of a single dose of tadalafil 10 mg or 20 mg, or placebo administered 2 hours after the tamsulosin. A washout period of at least 7 days was utilized to separate treatment periods. The mean maximal post-baseline decrease in standing SBP (primary endpoint) was greater for the doxazosin plus tadalafil treatment arm than it was in the doxazosin plus placebo arm, with a mean difference of 9.8 mmHg (95% CI, 4.1 to 15.5 mmHg) between the 2 groups. The mean maximal post-baseline decrease in standing SBP was similar after tamsulosin plus tadalafil 10 mg compared with tamsulosin plus placebo (mean difference, 1.7 mmHg; 95% CI, -4.7 to 8.1 mmHg) and after tamsulosin plus tadalafil 20 mg compared with tamsulosin plus placebo (mean difference, 2.3 mmHg; 95% CI, -4.1 to 8.7 mmHg) 5.
c) In drug-drug interaction studies, concomitant use of doxazosin and tadalafil was shown to augment the hypotensive effects of doxazosin 3.
Common questions
Can I take Doxazosin and Tadalafil together?
Increased risk of hypotension Always confirm with your pharmacist or prescriber before making any change.
How serious is the Doxazosin and Tadalafil interaction?
It is rated major. Potentially serious — often needs a change or close 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 strong is the evidence for this interaction?
The evidence is graded "established". Well documented — supported by controlled studies or strong clinical data.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Doxazosin or Tadalafil 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 a safer alternative to one of these medications for me?
References (5)
- Product Information: OPSYNVI(R) oral tablets, macitentan tadalafil oral tablets. Actelion Pharmaceuticals US, Inc. (Per FDA), Titusville, NJ, 2024. DailyMed
- Product Information: CARDURA(R) oral tablets, doxazosin oral tablets. Roerig (per FDA), New York, NY, 2021. DailyMed
- Product Information: Cialis(R) oral tablet, tadalafil oral tablet. Lilly USA, LLC (per DailyMed), Indianapolis, IN, 2023. DailyMed
- Product Information: ADCIRCA(R) oral tablets, tadalafil oral tablets. Eli Lilly and Company (per FDA), Indianapolis, IN, 2020. DailyMed
- Kloner RA, Jackson G, Emmick JT, et al: Interaction between the phosphodiesterase 5 inhibitor, tadalafil and 2 alpha-blockers, doxazosin and tamsulosin in healthy normotensive men. J Urol 2004; 172:1935-1940.
Keep reading about Tadalafil
Keep reading about Doxazosin
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
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