Tadalafil and Terazosin: Can They Be Taken Together?

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What is tadalafil and how does it work?

Tadalafil is the generic name for Cialis, a medicine licensed in the UK to treat erectile dysfunction (ED). It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing more blood to flow in when you are sexually aroused [4]. Unlike some other ED treatments, tadalafil has a long duration of action—its effects can last up to 36 hours, which is why it's sometimes called the 'weekend pill'.

Tadalafil is available in two ways: on-demand tablets (usually 10 mg or 20 mg) taken at least 30 minutes before sexual activity, or daily low-dose tablets (2.5 mg or 5 mg) taken once a day at the same time [4]. Both options require sexual stimulation to work—tadalafil does not cause an automatic erection. The medicine is only available on prescription in the UK after a consultation with a prescriber, who will check your medical history and current medicines to ensure it is safe for you.

What is terazosin and why is it prescribed?

Terazosin is an alpha-blocker, a type of medicine that relaxes certain muscles in blood vessels and the prostate gland. It is commonly prescribed to treat high blood pressure (hypertension) and to relieve urinary symptoms caused by an enlarged prostate (benign prostatic hyperplasia, or BPH) [3]. By blocking alpha receptors, terazosin allows blood vessels to widen and reduces resistance in the bladder neck and prostate, making it easier to urinate.

Because terazosin lowers blood pressure, it is usually started at a low dose and increased gradually to reduce the risk of dizziness or fainting, especially when standing up. Common side effects include dizziness, headache, tiredness, and a drop in blood pressure when you stand (postural hypotension). If you have been prescribed terazosin, it is important to take it exactly as directed and to inform any prescriber about it before starting a new medicine, including treatments for erectile dysfunction.

Why men on terazosin may also need ED treatment

Erectile dysfunction is more common in men with prostate problems or high blood pressure, and some men taking terazosin for these conditions may also experience ED [1]. While terazosin itself is not a common cause of erectile dysfunction, the underlying health conditions it treats—such as cardiovascular disease and diabetes—are known risk factors for ED [10]. This is why it is not unusual for a man to be prescribed both an alpha-blocker like terazosin and a PDE5 inhibitor like tadalafil.

When to get urgent help

• Chest pain or discomfort during or after sexual activity—call 999 or go to A&E immediately
• An erection lasting longer than four hours (priapism)—go to A&E straight away
• Sudden loss of vision in one or both eyes, or sudden loss of hearing—seek urgent medical help
• Fainting or severe dizziness that does not improve—contact your GP or call 111 for same-day advice
• Swelling of the face, lips, or throat, or difficulty breathing—call 999 or go to A&E

Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.

How do tadalafil and terazosin interact?

Tadalafil and terazosin can interact because both medicines have blood-pressure-lowering effects. When taken together, they can add to each other's effects and cause a more significant drop in blood pressure than either medicine alone [3][4]. This can lead to symptoms such as dizziness, light-headedness, fainting, or feeling unsteady, particularly when standing up quickly. In some cases, the drop in blood pressure can be serious.

The interaction occurs because tadalafil relaxes blood vessels throughout the body (not just in the penis), while terazosin also widens blood vessels as part of its action on alpha receptors. The combination is not absolutely contraindicated—unlike the dangerous interaction between tadalafil and nitrates—but it does require careful management. The key is to ensure you are stable on your alpha-blocker before starting tadalafil, and to begin with the lowest effective dose of the ED medicine [3][4].

Your prescriber will assess whether it is safe for you to take both medicines together. They will consider how long you have been on terazosin, whether your dose is stable, your blood pressure readings, and any history of dizziness or fainting. If the combination is appropriate, you will be advised to start on a low dose of tadalafil and to be cautious when standing up, especially in the first few days.

What your prescriber will check before combining these medicines

Before prescribing tadalafil to someone taking terazosin, a UK prescriber will carry out a thorough assessment. They will ask how long you have been on terazosin and whether your dose has been stable, because it is important that you are well-established on the alpha-blocker before adding a PDE5 inhibitor [3][4]. They will also check your blood pressure, ask about any episodes of dizziness or fainting, and review your full list of medicines to identify any other interactions.

The prescriber will also assess whether sexual activity is safe for you. Conditions such as recent heart attack or stroke, unstable angina, severe heart failure, or very low blood pressure mean that ED treatment may not be suitable [2][4]. If you are taking nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called 'poppers', you must not take tadalafil, as the combination can cause a dangerous fall in blood pressure [3][4].

If the prescriber decides that tadalafil is appropriate for you, they will recommend starting with the lowest dose—usually 10 mg on-demand or 2.5 mg daily—and will advise you on how to take it safely alongside terazosin. You should never adjust the dose of either medicine yourself, and you should report any new symptoms such as persistent dizziness, fainting, or chest pain.

Why you must declare all your medicines

It is essential to tell your prescriber about every medicine you take, including over-the-counter products, herbal remedies, and recreational drugs. Some medicines can interact with tadalafil in ways that are not immediately obvious—for example, potent CYP3A4 inhibitors like ritonavir or ketoconazole can raise tadalafil levels in the blood, increasing the risk of side effects [4]. Similarly, other blood-pressure medicines can add to the blood-pressure-lowering effect of tadalafil and terazosin. Your prescriber will check every medicine during your consultation to ensure the combination is safe.

At a glance

Practical advice for taking tadalafil and terazosin together

If your prescriber has approved the combination of tadalafil and terazosin, there are several practical steps you can take to minimise the risk of side effects. First, always start with the lowest recommended dose of tadalafil and do not increase it without medical advice. Take your time when standing up from sitting or lying down, especially in the first few days, to reduce the risk of dizziness or fainting. Avoid heavy alcohol, as it can lower blood pressure further and make erectile dysfunction worse [1][4].

Take tadalafil exactly as prescribed. If you are using the on-demand tablets, take them at least 30 minutes before sexual activity; if you are on the daily dose, take it at the same time each day. Do not take more than one dose in 24 hours, and never combine tadalafil with another PDE5 inhibitor (such as sildenafil or vardenafil) or with nitrates, nicorandil, riociguat, or poppers [3][4]. If you experience persistent dizziness, fainting, chest pain during sex, or an erection lasting more than four hours, seek medical help immediately.

Keep all your medicines in their original packaging and check the expiry dates. Store them at room temperature, away from moisture and direct sunlight. If you are prescribed a new medicine by another doctor or buy something over the counter, always check with a pharmacist whether it is safe to take with tadalafil and terazosin. Do not stop or change the dose of terazosin without consulting your GP, as this could affect your blood pressure or prostate symptoms.

When to seek medical help and warning signs to watch for

While most men tolerate the combination of tadalafil and terazosin well when prescribed appropriately, it is important to know the warning signs that require urgent medical attention. If you experience chest pain or discomfort during or after sexual activity, stop what you are doing and seek help immediately—call 999 or go to A&E [1][4]. Do not take nitrate medicines (such as GTN spray) if you have used tadalafil in the past 48 hours, as this can cause a dangerous drop in blood pressure.

An erection that lasts longer than four hours (priapism) is a medical emergency and requires immediate treatment to prevent permanent damage to the penis [4]. Sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing (sometimes with ringing in the ears or dizziness), are rare but serious side effects that need urgent assessment [4]. If you faint, have severe or persistent dizziness, or feel your heart racing or pounding, contact your GP or call 111 for advice.

Less urgent but still important: if you develop new symptoms such as swelling of the face, lips, or throat, difficulty breathing, or a severe skin rash, stop taking tadalafil and seek medical advice the same day. If the medicine does not help your erections after several attempts, or if you have side effects that bother you, speak to your prescriber—they may adjust your dose or suggest an alternative treatment. Never buy ED medicines from unregulated websites, as they may be counterfeit, unsafe, or interact dangerously with your other medicines.

Why regular reviews matter

If you are taking both tadalafil and terazosin long-term, your GP or prescriber should review your treatment regularly. This is to check that both medicines are still needed, that your blood pressure is well controlled, and that you are not experiencing troublesome side effects. Erectile dysfunction can be an early warning sign of heart disease or diabetes, so if ED is a new problem, it is important to see your GP for a full assessment [1][2]. Regular reviews also give you the opportunity to discuss any concerns, ask about lifestyle changes that can help ED, and ensure your treatment plan is still right for you.

In summary

• Tadalafil and terazosin can be taken together, but only under medical supervision and with specific precautions.
• Both medicines lower blood pressure, so the combination can cause dizziness or fainting if not managed carefully.
• You must be stable on terazosin before starting tadalafil, and you will begin on the lowest dose.
• Always declare all your medicines during your consultation so your prescriber can check for interactions.
• Seek urgent help if you experience chest pain, an erection lasting over four hours, or sudden vision or hearing loss.

Frequently Asked Questions