Sinalfa: Uses, Dosage & Side Effects
An alpha-1 adrenergic blocker containing terazosin, used to treat benign prostatic hyperplasia (BPH) and hypertension by relaxing smooth muscle in the prostate and blood vessels
Sinalfa (terazosin) is a selective alpha-1 adrenergic receptor blocker prescribed for the treatment of benign prostatic hyperplasia (BPH) and high blood pressure (hypertension). It works by relaxing smooth muscle in the prostate gland and in peripheral blood vessels, making it easier to urinate and reducing blood pressure. Sinalfa is taken once daily as a tablet, with dosing typically starting low and gradually increasing over several weeks. It is a prescription-only medication available in strengths of 1 mg, 2 mg, 5 mg, and 10 mg. Terazosin has been used in clinical practice for decades and is supported by extensive clinical evidence for both BPH symptom relief and blood pressure management.
Quick Facts: Sinalfa
Key Takeaways
- Sinalfa (terazosin) is an alpha-1 blocker that relaxes smooth muscle in the prostate and blood vessels, used to treat BPH symptoms and high blood pressure.
- Treatment starts at a low dose (1 mg at bedtime) and is gradually increased over several weeks to minimize the risk of first-dose hypotension and dizziness.
- Dizziness upon standing is the most common side effect, especially at the beginning of treatment or when increasing the dose.
- Inform your eye surgeon before cataract surgery if you take or have taken Sinalfa, as it can cause intraoperative floppy iris syndrome (IFIS).
- Do not combine with PDE5 inhibitors (sildenafil, tadalafil, vardenafil) without medical supervision, as the combined blood pressure-lowering effect may cause fainting.
What Is Sinalfa and What Is It Used For?
Sinalfa belongs to a class of medications known as alpha-1 adrenergic receptor blockers (alpha-blockers). These drugs work by selectively blocking alpha-1 receptors found in smooth muscle tissue throughout the body, particularly in the prostate gland, bladder neck, and blood vessel walls. By blocking these receptors, terazosin causes the smooth muscle to relax, which produces two clinically important effects depending on the condition being treated.
In benign prostatic hyperplasia (BPH), the prostate gland gradually enlarges as men age, compressing the urethra and obstructing urinary flow. Sinalfa relaxes the smooth muscle within the prostate gland and at the bladder neck, thereby reducing the mechanical obstruction of the urethra. This leads to a measurable improvement in urinary flow rate and a reduction in bothersome lower urinary tract symptoms (LUTS) such as difficulty initiating urination, weak stream, incomplete bladder emptying, frequent urination, and nocturia (waking at night to urinate). Clinical studies have demonstrated that terazosin improves the International Prostate Symptom Score (IPSS) by an average of 4-6 points and increases peak urinary flow rate by 1.5-3.0 mL/s.
In hypertension, Sinalfa reduces blood pressure by dilating the small peripheral blood vessels (arterioles). Unlike some older non-selective alpha-blockers, terazosin does not act directly on the vascular smooth muscle wall but works through the sympathetic nervous system by blocking the nerve signals that normally constrict these vessels. This mechanism reduces total peripheral vascular resistance, thereby lowering both systolic and diastolic blood pressure. Sinalfa is often used in combination with other antihypertensive agents such as diuretics, beta-blockers, ACE inhibitors, or calcium channel blockers for optimal blood pressure control.
Terazosin has a favorable metabolic profile compared to some other antihypertensive agents. Studies have shown it may have mild beneficial effects on lipid profiles, including modest reductions in total cholesterol and LDL cholesterol, as well as small increases in HDL cholesterol. It does not adversely affect glucose metabolism, making it a suitable option for patients with diabetes who also have BPH or hypertension. The European Association of Urology (EAU) guidelines list alpha-blockers including terazosin as first-line pharmacological treatment for moderate-to-severe LUTS associated with BPH.
Terazosin, the active ingredient in Sinalfa, may also be approved for other conditions not listed here. Always follow your doctor's instructions and consult your healthcare provider or pharmacist if you have any questions about your medication.
What Should You Know Before Taking Sinalfa?
Before starting treatment with Sinalfa, it is essential to have a thorough discussion with your prescribing physician about your complete medical history, current medications, and any known allergies. Certain conditions and circumstances may make Sinalfa unsuitable or require special precautions during treatment. Understanding these factors before you begin taking the medication helps ensure your safety and allows your doctor to tailor the treatment plan to your individual needs.
Contraindications
You should not take Sinalfa if any of the following apply to you:
- Allergy to terazosin: If you have a known hypersensitivity to terazosin hydrochloride or any of the inactive ingredients in the tablet formulation (including lactose, maize starch, pregelatinized starch, talc, or magnesium stearate).
- Allergy to other alpha-blockers: If you have experienced an allergic reaction to other alpha-1 adrenergic receptor blockers such as doxazosin, prazosin, alfuzosin, or tamsulosin, there is a risk of cross-sensitivity with terazosin.
- History of syncope during micturition: If you have previously experienced fainting (syncope) upon standing up and urinating, you should not use this medication as it may worsen this condition.
Sinalfa is not recommended for use in children, as safety and efficacy in the pediatric population have not been established.
Warnings and Precautions
Talk to your doctor or pharmacist before taking Sinalfa if you have any of the following conditions or circumstances:
- Impaired liver function: Since terazosin is extensively metabolized by the liver, patients with hepatic impairment may have altered drug metabolism, potentially leading to higher plasma concentrations and an increased risk of side effects. Your doctor may need to adjust your dose or monitor you more closely.
When you first start taking Sinalfa, when your dose is increased, or when treatment is resumed after an interruption, you may experience a sudden drop in blood pressure upon standing up quickly (orthostatic hypotension). This can cause dizziness, lightheadedness, or in some cases, fainting. To reduce this risk, take your first dose at bedtime and stand up slowly from sitting or lying positions. The risk of low blood pressure is higher if you are also taking certain other medications (see Drug Interactions section).
If you are scheduled for eye surgery to treat cataracts (clouding of the lens), inform your ophthalmologist before the operation that you are taking or have previously taken Sinalfa. Alpha-blockers like terazosin can cause a condition known as intraoperative floppy iris syndrome (IFIS), which may complicate the surgical procedure. When your surgeon is informed in advance, they can take appropriate precautions to manage this condition safely.
Pregnancy and Breastfeeding
If you are pregnant, think you may be pregnant, are planning to become pregnant, or are breastfeeding, consult your doctor or pharmacist before taking Sinalfa.
Pregnancy: There is limited clinical experience with the use of terazosin during human pregnancy. Animal reproduction studies have not demonstrated teratogenic effects, but the absence of human data means that the potential risks to the developing fetus cannot be fully excluded. Sinalfa should only be used during pregnancy after careful consideration by your doctor, weighing the potential benefits of treatment against the possible risks to the unborn child. As BPH is a condition affecting men, pregnancy is not typically relevant for the primary indication; however, if prescribed for hypertension in women, this consideration becomes important.
Breastfeeding: It is currently unknown whether terazosin passes into human breast milk. Because many drugs are excreted in breast milk and because of the potential for adverse reactions in nursing infants, a decision should be made whether to discontinue breastfeeding or discontinue the drug, taking into account the importance of the medication for the mother. Consult your healthcare provider for personalized advice.
Driving and Operating Machinery
Sinalfa can have a noticeable effect on your ability to drive and use machines. Some patients may experience impaired reaction time, particularly at the beginning of treatment and when doses are changed. Dizziness, drowsiness, and blurred vision are known side effects that can affect your alertness and coordination. You are personally responsible for assessing whether you are fit to drive a motor vehicle or perform work requiring alertness. If you experience any of these symptoms, avoid driving or operating machinery until you know how the medication affects you. Discuss any concerns with your doctor or pharmacist.
Sinalfa tablets contain lactose as an inactive ingredient. If you have been told by your doctor that you have an intolerance to certain sugars, contact your doctor before taking this medicine.
How Does Sinalfa Interact with Other Drugs?
Drug interactions can alter how Sinalfa works or increase the risk of serious side effects. It is crucial to tell your doctor or pharmacist about all medications you are currently taking, have recently taken, or might take, including prescription drugs, over-the-counter medications, and herbal supplements. The following interactions are particularly important to be aware of when using Sinalfa.
Major Interactions
The most clinically significant interactions with Sinalfa involve medications that also lower blood pressure, as the combined effect can lead to an excessive and potentially dangerous drop in blood pressure:
| Drug / Drug Class | Type of Interaction | Clinical Effect | Recommendation |
|---|---|---|---|
| PDE5 inhibitors (sildenafil, tadalafil, vardenafil) | Additive hypotension | Significant blood pressure drop, dizziness, fainting | Use with extreme caution; allow 4-6 hours between doses; start PDE5 inhibitor at lowest dose |
| Beta-blockers (metoprolol, atenolol, propranolol) | Enhanced hypotensive effect | Excessive blood pressure reduction, especially at start of treatment | Monitor blood pressure closely; initiate Sinalfa at the lowest dose |
| ACE inhibitors (enalapril, ramipril, lisinopril) | Enhanced hypotensive effect | Additive blood pressure lowering, dizziness on standing | Gradual dose titration; regular blood pressure monitoring |
| Diuretics (furosemide, hydrochlorothiazide) | Enhanced hypotensive effect | Increased risk of postural hypotension and dizziness | Monitor for symptoms of hypotension; adjust doses as needed |
| Calcium channel blockers (amlodipine, nifedipine, verapamil) | Enhanced hypotensive effect | Potentiated blood pressure reduction | Start at the lowest Sinalfa dose; careful monitoring during titration |
| Clonidine | Enhanced hypotensive effect | Pronounced blood pressure drop, especially initially | Close medical supervision when combining; gradual dose adjustments |
Other Considerations
While the interactions listed above are the most clinically relevant, there are additional considerations when taking Sinalfa:
- Other alpha-blockers: Taking Sinalfa with other alpha-adrenergic blocking agents (such as tamsulosin, doxazosin, or alfuzosin) should generally be avoided, as this may lead to excessive alpha-blockade and a higher risk of hypotension and related symptoms.
- NSAIDs: Non-steroidal anti-inflammatory drugs (such as ibuprofen and naproxen) may reduce the antihypertensive effect of terazosin. If you require regular NSAID use, your doctor may need to monitor your blood pressure more frequently.
- Alcohol: Alcohol consumption can enhance the blood pressure-lowering effect of Sinalfa and increase the risk of dizziness, lightheadedness, and fainting. Limit alcohol intake, especially when starting treatment or increasing the dose.
- Sympathomimetics: Medications that stimulate the sympathetic nervous system (such as pseudoephedrine found in some cold and flu remedies) may counteract the blood pressure-lowering effect of Sinalfa.
Always carry an up-to-date list of all your medications and share it with every healthcare provider involved in your care. This helps prevent potentially harmful drug interactions and ensures that your treatment plan is both safe and effective.
What Is the Correct Dosage of Sinalfa?
Always take Sinalfa exactly as your doctor has prescribed. Do not change the dose or stop taking the medication without consulting your doctor first. The dose is individualized based on your condition, response to treatment, and tolerability. A gradual dose titration (starting low and slowly increasing) is essential to minimize the risk of first-dose hypotension and related side effects.
Dosage for Benign Prostatic Hyperplasia (BPH)
BPH Dose Titration Schedule
| Week | Dose | Timing | Notes |
|---|---|---|---|
| Week 1 | 1 mg | At bedtime | Starting dose; take at bedtime to reduce risk of first-dose hypotension |
| Week 2 | 2 mg | At bedtime | First dose increase; starter pack contains 7 x 1 mg + 7 x 2 mg tablets |
| Week 3 | 5 mg | At bedtime | Continued titration based on response and tolerability |
| Week 4+ | 5-10 mg | At bedtime | Maintenance dose as directed by your doctor |
A convenient starter pack is available containing the first 14 tablets (7 tablets of 1 mg and 7 tablets of 2 mg) to facilitate the initial dose titration. Be careful to take the correct strength tablet during each phase.
Dosage for Hypertension
Hypertension Dose Titration Schedule
| Period | Dose | Timing | Notes |
|---|---|---|---|
| Days 1-4 | 1 mg | At bedtime | Starting dose; take at bedtime to minimize first-dose effect |
| Days 5-7 | 1 mg | In the morning | Switch to morning dosing once tolerability is established |
| Week 2 | 2 mg | In the morning | First dose increase; monitor blood pressure response |
| Week 3 | 5 mg | In the morning | Increase if blood pressure target not achieved |
| Week 4+ | 5-20 mg | In the morning | Further titration may be needed; maximum recommended dose is 20 mg/day |
For hypertension, Sinalfa is often used in combination with other antihypertensive medications. Your doctor will determine the optimal dose based on your individual blood pressure response.
Elderly Patients
No specific dose adjustment is routinely recommended for elderly patients based solely on age. However, older adults are generally more susceptible to the blood pressure-lowering effects of alpha-blockers and may be at higher risk of orthostatic hypotension, falls, and related injuries. Your doctor will likely start with the lowest available dose and titrate more slowly, with careful monitoring of blood pressure (including standing blood pressure measurements) and symptoms of postural dizziness. If you are taking multiple medications that lower blood pressure, extra caution is advised.
Missed Dose
If you forget to take a dose of Sinalfa, take it as soon as you remember, unless it is nearly time for your next scheduled dose. In that case, skip the missed dose and take your next dose at the regular time. Do not take a double dose to make up for a forgotten tablet. If you have missed several consecutive doses, consult your doctor before resuming treatment, as your dose may need to be re-titrated from the starting level to avoid first-dose hypotension.
Overdose
If you have taken too much Sinalfa, or if a child has accidentally swallowed any tablets, contact your doctor, hospital emergency department, or local poison control center immediately for assessment and advice. An overdose of terazosin may cause severe hypotension (dangerously low blood pressure), drowsiness, and shock. Keep the patient lying down with legs elevated to maintain blood flow to vital organs until medical help arrives.
Do not stop taking Sinalfa abruptly or change the dosage on your own without first consulting your doctor. Sudden discontinuation is not typically associated with rebound hypertension, but your underlying condition will no longer be treated. If you have any further questions about your dosage or how to take this medication, ask your doctor, pharmacist, or nurse.
What Are the Side Effects of Sinalfa?
Like all medicines, Sinalfa can cause side effects, although not everyone experiences them. Most side effects are mild to moderate and tend to occur at the beginning of treatment or when the dose is increased. They often diminish as your body adjusts to the medication. However, some side effects can be serious and require prompt medical attention.
Stop taking Sinalfa and contact your doctor or seek emergency medical care immediately if you experience: shortness of breath or difficulty breathing; swelling of the face, tongue, or throat; difficulty swallowing; hives combined with breathing problems. These may be symptoms of angioedema, a rare but potentially life-threatening allergic reaction.
Very Common
Affects more than 1 in 10 patients
- Dizziness (especially upon standing up, most common at start of treatment and dose increases, affecting approximately 10-15% of patients)
Common
Affects up to 1 in 10 patients
- Drowsiness (somnolence)
- Fatigue and weakness (asthenia)
- Headache
- Blurred vision
- Orthostatic hypotension (drop in blood pressure when standing)
- Palpitations (sensation of rapid or irregular heartbeat)
- Peripheral edema (swelling of ankles, feet, or hands)
- Nasal congestion (stuffy nose)
- Nausea
- Erectile dysfunction (impotence)
Uncommon
Affects up to 1 in 100 patients
- Syncope (fainting)
Rare
Affects up to 1 in 1,000 patients
- Thrombocytopenia (decreased blood platelet count)
- Atrial fibrillation (irregular heart rhythm)
- Urinary incontinence
- Priapism (painful, prolonged erection lasting more than 4 hours — seek immediate medical attention)
Frequency Not Known
Cannot be estimated from available data
- Skin hypersensitivity reactions (rash, itching, redness)
- Depression
- Vertigo
- Visual impairment
- Tachycardia (rapid heartbeat)
- Urinary tract infection
- Decreased libido (reduced sexual desire)
- Fluid retention and edema
The risk and severity of many side effects can be minimized by following the recommended dose titration schedule, starting at a low dose and increasing gradually. If any side effect becomes bothersome or does not resolve, or if you notice any effect not listed above, tell your doctor or pharmacist. You should also report any suspected adverse reactions to your national pharmacovigilance authority, as this helps continuously monitor the benefit-risk balance of the medicine.
It is worth noting that dizziness, the most commonly reported side effect, typically occurs when rising from a sitting or lying position (orthostatic effect). Simple measures such as rising slowly, sitting on the edge of the bed for a moment before standing, and avoiding sudden changes in posture can significantly reduce the frequency and severity of this symptom. Staying well hydrated and avoiding excessive heat exposure can also help.
How Should You Store Sinalfa?
Proper storage of medications is important to ensure their effectiveness and safety. Follow these guidelines to store Sinalfa correctly:
- Keep out of sight and reach of children. Store Sinalfa in a secure location where children cannot access it. Consider using a child-resistant cabinet or container.
- Check the expiry date. Do not use Sinalfa after the expiry date printed on the packaging (marked "EXP"). The expiry date refers to the last day of that month. Using expired medication may be less effective or potentially harmful.
- Store at room temperature. Keep the tablets in their original blister packaging to protect them from moisture. No special temperature storage conditions are required, but avoid extreme heat or humidity.
- Dispose of properly. Do not throw medications away via household waste or flush them down the toilet or drain. Return any unused or expired medication to your pharmacy for safe disposal. These measures help protect the environment from pharmaceutical contamination.
If you notice any change in the appearance of the tablets (discoloration, crumbling, or unusual odor), do not take them and consult your pharmacist for a replacement.
What Does Sinalfa Contain?
Understanding what your medication contains is important, especially if you have known allergies or intolerances. Below is a detailed breakdown of the active and inactive ingredients in Sinalfa tablets.
Active Substance
The active pharmaceutical ingredient in Sinalfa is terazosin hydrochloride, which is equivalent to the following amounts of terazosin (the therapeutically active form):
- 1 mg terazosin per tablet
- 2 mg terazosin per tablet
- 5 mg terazosin per tablet
- 10 mg terazosin per tablet
Inactive Ingredients (Excipients)
The inactive ingredients are the same across all tablet strengths, with the exception of colorants used to distinguish between different strengths:
| Strength | Colorant | Common Excipients |
|---|---|---|
| 1 mg | None (white tablet) | Lactose, maize starch, pregelatinized starch, talc, magnesium stearate |
| 2 mg | Quinoline yellow (E104) | Lactose, maize starch, pregelatinized starch, talc, magnesium stearate |
| 5 mg | Iron oxide (E172) | Lactose, maize starch, pregelatinized starch, talc, magnesium stearate |
| 10 mg | Indigotine (E132) | Lactose, maize starch, pregelatinized starch, talc, magnesium stearate |
Available Pack Sizes
Sinalfa is supplied in blister packs in the following configurations:
- Starter pack: 1 mg x 7 tablets + 2 mg x 7 tablets (14 tablets total, designed for the initial dose titration in BPH)
- 2 mg tablets: 28 or 98 tablets per pack
- 5 mg tablets: 28 or 98 tablets per pack
- 10 mg tablets: 28 or 98 tablets per pack
Not all pack sizes may be marketed in every country. Your pharmacist can advise you on which pack sizes are available in your area.
Frequently Asked Questions About Sinalfa
Both Sinalfa (terazosin) and tamsulosin are alpha-blockers used to treat BPH, but they differ in selectivity and side effect profiles. Tamsulosin is a more selective alpha-1A blocker, meaning it preferentially targets receptors in the prostate with less effect on blood vessels, resulting in fewer blood pressure-related side effects. Terazosin, on the other hand, is a non-selective alpha-1 blocker that affects both prostate and vascular receptors, which makes it useful for patients who have both BPH and hypertension. However, terazosin is more likely to cause orthostatic hypotension and dizziness. Your doctor will choose the most appropriate alpha-blocker based on your individual medical profile and whether you also need blood pressure management.
No, Sinalfa does not shrink the prostate gland. It works by relaxing the smooth muscle in the prostate and bladder neck, which relieves the mechanical obstruction of the urethra and improves urinary symptoms. For actual prostate size reduction, 5-alpha reductase inhibitors such as finasteride or dutasteride are used. These work by blocking the conversion of testosterone to dihydrotestosterone (DHT), which drives prostate growth. In some cases, doctors may prescribe both an alpha-blocker like Sinalfa and a 5-alpha reductase inhibitor together (combination therapy) for men with significantly enlarged prostates and moderate-to-severe symptoms, as this combination has been shown in large clinical trials to be more effective than either drug alone.
Taking Sinalfa at bedtime, especially during the initial dose titration phase, is recommended to minimize the impact of first-dose hypotension. When you first start the medication or increase the dose, there is a risk of your blood pressure dropping significantly, which can cause dizziness, lightheadedness, or even fainting. By taking the tablet at bedtime, the peak blood pressure-lowering effect occurs while you are lying down and asleep, reducing the chance that you will stand up quickly and experience symptoms. Once your body adjusts to the medication and the dose is stable, your doctor may advise switching to morning dosing, particularly if you are taking Sinalfa for hypertension.
Priapism (a painful erection lasting more than 4 hours) is a rare but serious side effect of alpha-blockers including terazosin. If you experience a persistent, painful erection, seek immediate emergency medical attention. Priapism is a medical emergency because prolonged blood engorgement can cause permanent damage to the erectile tissue of the penis if not treated promptly. Do not wait for the erection to resolve on its own. Treatment in the emergency department typically involves drainage of blood from the penis and/or injection of a sympathomimetic agent.
You should be cautious about drinking alcohol while taking Sinalfa. Alcohol is a vasodilator that can lower blood pressure on its own, and when combined with Sinalfa, the blood pressure-lowering effect can be additive, increasing the risk of dizziness, lightheadedness, and fainting. This is especially true at the beginning of treatment, during dose adjustments, or if you consume a large amount of alcohol in a short period. If you do choose to drink alcohol, do so in moderation, be aware of how it affects you, and rise slowly from sitting or lying positions. Discuss your alcohol consumption with your doctor for personalized guidance.
Unlike some other blood pressure medications (such as beta-blockers or clonidine), abruptly stopping terazosin does not typically cause rebound hypertension or withdrawal symptoms. However, stopping the medication means that your BPH symptoms or high blood pressure will no longer be treated, and symptoms may return. Additionally, if you stop taking Sinalfa for more than a few days and then want to restart, you will generally need to begin again at the lowest dose (1 mg) and re-titrate upward, as the risk of first-dose hypotension returns after a break in treatment. Always consult your doctor before making any changes to your medication regimen.
References
- European Medicines Agency (EMA). Terazosin – Summary of Product Characteristics. European Medicines Agency. Updated 2025.
- U.S. Food and Drug Administration (FDA). Hytrin (Terazosin Hydrochloride) – Prescribing Information. FDA Approved Drug Products. Updated 2024.
- Gravas S, Cornu JN, Gacci M, et al. EAU Guidelines on Management of Non-Neurogenic Male Lower Urinary Tract Symptoms (LUTS), incl. Benign Prostatic Obstruction (BPO). European Association of Urology. 2024.
- Lerner LB, McVary KT, Barry MJ, et al. Management of Lower Urinary Tract Symptoms Attributed to Benign Prostatic Hyperplasia: AUA Guideline Amendment 2023. Journal of Urology. 2023;210(1):16-19.
- National Institute for Health and Care Excellence (NICE). Hypertension in adults: diagnosis and management (NG136). NICE Guidelines. Updated 2023.
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List. World Health Organization. 2023.
- Lepor H. Alpha-blockers for the treatment of benign prostatic hyperplasia. Urologic Clinics of North America. 2016;43(3):311-323.
- Djavan B, Marberger M. A meta-analysis on the efficacy and tolerability of alpha1-adrenoceptor antagonists in patients with lower urinary tract symptoms suggestive of benign prostatic obstruction. European Urology. 1999;36(1):1-13.
- McConnell JD, Roehrborn CG, Bautista OM, et al. The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of benign prostatic hyperplasia (MTOPS trial). New England Journal of Medicine. 2003;349(25):2387-2398.
- British National Formulary (BNF). Terazosin. National Institute for Health and Care Excellence. 2025.
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