Can Terazosin and Tadalafil Be Taken Together? What You Need to Know

October 13, 2025 •

5 min read

According to studies, combining terazosin with PDE5 inhibitors like tadalafil can cause a potentially significant drop in blood pressure, known as hypotension. This interaction is a serious concern for individuals managing conditions like benign prostatic hyperplasia (BPH) or erectile dysfunction (ED) with these medications. Due to their similar effects of relaxing blood vessels, taking terazosin and tadalafil together without proper medical supervision is not recommended and can increase the risk of adverse side effects.

Quick Summary

Taking terazosin and tadalafil concurrently is associated with a moderate to high risk of a serious drug interaction. This combination can lead to a dangerous drop in blood pressure, causing dizziness, fainting, and lightheadedness due to their individual and combined blood pressure-lowering effects. Medical supervision is essential to manage potential risks and adjust dosing strategies.

Key Points

High-Risk Combination: Combining terazosin and tadalafil is a high-risk practice due to their synergistic blood pressure-lowering effects, which can cause severe hypotension.
Orthostatic Hypotension: The primary risk is orthostatic hypotension, a sudden and dangerous drop in blood pressure upon standing, leading to dizziness, lightheadedness, or fainting.
Expert Medical Supervision Required: Any use of these medications together must be managed by a healthcare provider, who will likely start with low doses and monitor blood pressure closely.
Stabilization Before Co-Administration: Patients must be on a stable dose of one medication before starting the other to minimize the risk of a severe hypotensive event.
BPH Combination Not Recommended: The combination of terazosin and tadalafil is not typically recommended for BPH due to insufficient safety and efficacy data for this specific use.
Safe Alternatives Exist: For BPH and ED treatment, a doctor may recommend switching to tadalafil monotherapy (discontinuing terazosin first) as a safer alternative.
Avoid Alcohol and Grapefruit: Both terazosin and tadalafil can interact with alcohol and grapefruit juice, further increasing the risk of low blood pressure.
Recognize and Report Symptoms: Patients should be vigilant for symptoms of hypotension, such as dizziness or fainting, and report them to their doctor immediately.

The Pharmacological Basis for the Interaction

To understand why combining terazosin and tadalafil can be hazardous, it's essential to examine how each medication works independently. Both drugs affect the body's blood vessels, albeit through different mechanisms. Their combined action can lead to a synergistic, and potentially dangerous, effect on blood pressure.

How Terazosin Works

Terazosin belongs to a class of drugs known as alpha-blockers. It is prescribed to treat high blood pressure (hypertension) and the symptoms of benign prostatic hyperplasia (BPH), such as urinary frequency and weak stream. Terazosin works by blocking alpha-1 adrenergic receptors, which causes the muscles in the blood vessels, prostate, and bladder neck to relax. This relaxation allows blood to flow more easily, lowering blood pressure and improving urinary flow.

How Tadalafil Works

Tadalafil, a phosphodiesterase type 5 (PDE5) inhibitor, is primarily used to treat erectile dysfunction (ED) and, in lower daily doses, the symptoms of BPH and pulmonary arterial hypertension (PAH). Tadalafil inhibits the PDE5 enzyme, which breaks down cyclic guanosine monophosphate (cGMP), a substance that regulates blood flow in the penis and other smooth muscle tissues. By preserving cGMP, tadalafil promotes the relaxation of smooth muscles and increases blood flow, which facilitates an erection in response to sexual stimulation. As a secondary effect, this vasodilation can also cause a slight decrease in blood pressure.

The Danger of Combined Vasodilation

The risk arises because both terazosin and tadalafil cause vasodilation, or the widening of blood vessels. When taken together, their hypotensive (blood pressure-lowering) effects are compounded, leading to a much more significant and sudden drop in blood pressure than either drug alone would cause. This can result in orthostatic hypotension, a condition where blood pressure falls rapidly upon standing up, which can cause severe dizziness, lightheadedness, and fainting.

Recommendations for Co-Administration

Despite the risks, some men may need treatment for both BPH and ED. In these cases, it is crucial that the co-administration of terazosin and tadalafil is managed carefully under strict medical supervision. The FDA and clinical guidelines provide specific recommendations to minimize the risk of a severe hypotensive event.

Initial Stabilization: The patient must be on a stable, optimal dose of one medication before starting the other. This ensures their body has adjusted to the blood pressure effects of the first drug before adding the second.
Lowest Starting Dose: When introducing the second medication, the lowest possible dose should be used. For example, if a patient is stable on terazosin, they should begin tadalafil at the lowest dose (e.g., 2.5 mg) and have their blood pressure closely monitored.
Timing of Doses: Separating the administration of the two medications can help mitigate the peak hypotensive effects. A patient might take their alpha-blocker in the morning and their PDE5 inhibitor at another time, but only if their doctor recommends this strategy.
Close Monitoring: Healthcare providers should monitor the patient's blood pressure regularly, particularly when initiating or adjusting doses. Patients should also be educated on the symptoms of hypotension.

Comparison of Terazosin and Tadalafil


Feature	Terazosin (Alpha-Blocker)	Tadalafil (PDE5 Inhibitor)
Primary Uses	Benign Prostatic Hyperplasia (BPH) and high blood pressure.	Erectile Dysfunction (ED), BPH, and Pulmonary Arterial Hypertension (PAH).
Mechanism of Action	Relaxes smooth muscles in blood vessels, prostate, and bladder neck by blocking alpha-1 receptors.	Inhibits the PDE5 enzyme, increasing cGMP and relaxing smooth muscles in the penis and other tissues.
Effect on Blood Pressure	Lowers blood pressure by widening blood vessels.	Lowers blood pressure due to its vasodilatory effects.
Duration	Can last for an extended period, often taken once or twice daily.	Long-acting, effective for up to 36 hours (as-needed dose) or taken once daily.
Interaction Risk	Increased risk of severe hypotension when combined with tadalafil.	Increased risk of severe hypotension when combined with terazosin.
Treatment for BPH	Approved as a standalone treatment for BPH.	Approved as a standalone daily treatment for BPH.
Combined Use for BPH	The combination of tadalafil and alpha-blockers is not recommended for BPH, as it lacks sufficient safety and efficacy data for this specific use.	The combination is not recommended for BPH treatment due to safety concerns and insufficient data.

Managing the Combination for BPH

While combining terazosin and tadalafil for BPH is generally not recommended due to safety and efficacy concerns, alternative strategies exist. Since tadalafil is approved as a once-daily treatment for BPH symptoms, a doctor may recommend switching a patient from terazosin to tadalafil monotherapy. The patient would need to discontinue the terazosin first, typically waiting at least one day before starting the daily tadalafil regimen.

In some cases, a healthcare provider might consider adding tadalafil for ED in a patient already stable on an alpha-blocker for BPH or hypertension. This is a complex decision that requires careful weighing of risks and benefits. When this approach is taken, the patient must be started on the lowest dose of tadalafil, and their response closely monitored to prevent severe hypotension. The combination of tadalafil with a 5-alpha reductase inhibitor like finasteride is also an alternative approach for BPH that can be considered.

Conclusion

While taking terazosin and tadalafil together is not strictly forbidden, it is a high-risk combination due to the significant and potentially dangerous drop in blood pressure it can cause. Both medications are vasodilators, and their combined effect can lead to symptomatic hypotension, with side effects such as dizziness, fainting, and headaches. For patients requiring treatment for both BPH and ED, a doctor can safely manage the risk by ensuring the patient is stable on one medication, starting the second at the lowest possible dose, and closely monitoring blood pressure. In some cases, transitioning to a single, low-dose daily medication like tadalafil for BPH may be the safest and most effective option. The decision to co-administer these drugs must always be made by a healthcare professional after a thorough evaluation of the patient's overall health.

Patients should never adjust their dosages or combine these medications without first consulting their doctor. The potential for a serious and life-threatening drop in blood pressure makes professional guidance essential.

Outbound Link

For more information on drug interactions, the U.S. Food and Drug Administration (FDA) provides extensive resources and drug labels: FDA Drug Information.

Frequently Asked Questions

Combining these two medications is risky because both are vasodilators, meaning they relax and widen blood vessels to lower blood pressure. Their combined effect can cause a much greater and more sudden drop in blood pressure than either drug alone, leading to a dangerous condition called hypotension.

Symptoms of dangerously low blood pressure, or hypotension, include dizziness, lightheadedness, blurred vision, fatigue, and fainting, especially when standing up quickly. If you experience these symptoms, you should sit or lie down and contact your doctor immediately.

This is not recommended without strict medical supervision. A healthcare provider might suggest a switch to daily tadalafil for BPH, after discontinuing terazosin, to treat both conditions simultaneously while managing blood pressure.

If a doctor approves co-administration, they may suggest staggering the doses to avoid the peak effects of both drugs at the same time. For example, taking one in the morning and the other later, but this should only be done under medical guidance.

If you mistakenly take both medications, monitor yourself for signs of low blood pressure, such as dizziness or feeling faint. If you experience these symptoms, lie down and contact your healthcare provider or seek emergency medical help immediately.

A safer approach is to use tadalafil alone, which is FDA-approved for both ED and BPH at a low daily dose. This eliminates the risk of a dangerous interaction with an alpha-blocker like terazosin.

Consuming alcohol with either medication, and especially with both, can amplify their blood pressure-lowering effects. It is strongly advised to limit or avoid alcohol to minimize the risk of severe hypotension.

Yes, it is crucial to inform your doctor about all prescription and non-prescription medications, vitamins, supplements, and herbal products you are taking. This allows them to check for potential drug interactions and ensure your safety.