How It Works
Doxazosin works by blocking the action of norepinephrine, a natural chemical in the body that signals muscle contraction. By inhibiting alpha-1 receptors, the medication relaxes certain muscles.
- For the prostate and bladder: Doxazosin relaxes the smooth muscles in the prostate gland and the neck of the bladder. This relaxation reduces the pressure on the urethra, allowing urine to flow more easily and helping the bladder empty.
- For blood pressure: Doxazosin relaxes the muscles in the walls of the blood vessels. When these vessels stay open and relaxed, blood can flow through them with less resistance, lowering blood pressure.
Doxazosin can help restore normal urinary function and reduce cardiovascular strain associated with hypertension.
| Quick Facts | |
|---|---|
| Common Brands | Cardura, Cardura XL |
| Drug Class | Alpha-1 blocker (Alpha antagonist) |
| Generic Status | Generic version available |
| Availability | Prescription only |
Dosing
Doxazosin generally requires a gradual ramp-up of the dosage to allow your body time to adjust to changes in blood pressure.
- Initial dosage: Providers typically recommend a starting dose of 1 mg once daily.
- Gradual increase: Depending on your response, your doctor may gradually increase the dose to 2 mg, 4 mg, or up to 8 mg for BPH (or 16 mg for hypertension).
- The first-dose rule: It is generally accepted that the first dose should be taken at bedtime. This is because the initial drop in blood pressure can be most significant when you first start the drug.
- Cardura XL: If you are prescribed the extended-release tablet, it is generally taken once daily with breakfast. These tablets must be swallowed whole and should not be crushed or chewed.
- Consistency: Providers advise taking the medication at the same time each day.
If you stop taking doxazosin for several days, it’s generally advised not to resume your full dose without first consulting your doctor, as you may need to restart at the lowest 1 mg dose to avoid a sudden drop in blood pressure.
Note: Dosing information below is educational only. Your prescribing physician will determine your specific dose based on your individual health needs. Always follow your healthcare provider’s instructions for exact dosing.
Uses
FDA-Approved Uses
The FDA approves doxazosin for the following medical conditions:
- Benign prostatic hyperplasia (BPH): To treat the urinary symptoms associated with an enlarged prostate
- Hypertension: To lower high blood pressure
Off-Label Uses
You may see doxazosin prescribed for uses that are not FDA-approved. This is a common and legal practice called off-label prescribing, where a doctor uses their clinical judgment to prescribe a drug for a different (but well-researched) purpose.
Doxazosin may be prescribed for the following conditions:
- Kidney stones: Some doctors prescribe doxazosin to help make it easier and less painful for a patient to pass a kidney stone.
- Raynaud’s phenomenon: It may be used to improve blood flow to the fingers and toes in people who experience severe cold-induced spasms of the blood vessels.
- Ureteral stent discomfort: It can help reduce the bladder spasms and pain associated with having a medical stent placed in the urinary tract.
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Side Effects
Like all medications that affect blood pressure and muscle relaxation, doxazosin can cause side effects. Many individuals find that these symptoms diminish as their body adjusts to the medication.
Common Side Effects
- Dizziness or lightheadedness, especially when standing up
- Fatigue or a general feeling of weakness
- Headache
- Drowsiness
- Swelling in the hands, ankles, or feet (fluid retention)
Serious Side Effects
Serious side effects are rare, but it’s important to know what to look for if they do occur. Stop taking the medication and immediately call the doctor if you experience any of the following symptoms:
- Orthostatic hypotension: A sudden, severe drop in blood pressure when standing up, which can lead to fainting.
- Priapism: A painful erection lasting longer than 4 hours. This is a medical emergency that requires immediate care to prevent permanent damage.
- Chest pain (angina): It’s generally advised to contact your doctor immediately if you experience new or worsening chest pain or a rapid, pounding heartbeat.
- Severe allergic reaction: Standard guidelines recommend monitoring for hives, facial or throat swelling, or difficulty breathing.
Call your doctor immediately if you experience any concerning or prolonged symptoms.
Pharmacist Tips
Rise Slowly
Because doxazosin can cause your blood pressure to drop when you stand up, providers typically recommend moving slowly from a lying to a sitting position and waiting a moment before standing.
The 24-Hour Rule
Standard guidelines recommend not driving or operating heavy machinery for at least 24 hours after your first dose or after any dose increase, as dizziness is most likely to occur during these times.
Bedtime Start
Taking your dose at night can help you sleep through the period when dizziness is most likely to occur.
Check Your Stool
If you take Cardura XL, you may see an empty tablet shell in your stool. This is normal. The medication has been absorbed and the shell is designed to pass through your system.
Eye Surgery Alert
If you are planning cataract or glaucoma surgery, it’s generally recommended to tell your eye surgeon you are taking doxazosin. It can cause a condition called floppy iris syndrome during the procedure.
Drug Interactions
Doxazosin can interact with other medications, particularly those that also lower blood pressure or affect blood flow. It’s generally recommended to let your doctor know if you take:
- Erectile dysfunction medications: Taking drugs like Viagra (sildenafil), Cialis (tadalafil), or Levitra (vardenafil) while on doxazosin can cause a dangerously low drop in blood pressure.
- Other blood pressure pills: Diuretics (water pills), beta-blockers, or ACE inhibitors can have an additive effect, making your blood pressure drop lower than intended.
- Cimetidine: This medication may increase the levels of doxazosin in your blood.
Always give your doctor and pharmacist a complete list of all your medications, vitamins, and supplements to check for potential interactions.
FAQs
Why did my doctor instruct me to take my first dose while sitting on the edge of my bed?
This is a safety precaution. The first dose of doxazosin often causes a more pronounced drop in blood pressure than subsequent doses. Sitting or lying down ensures that if you feel dizzy or faint, you are in a safe position and less likely to fall.
Should I take doxazosin before I go to sleep?
For the immediate-release version, many providers recommend bedtime dosing to minimize the impact of daytime dizziness. However, the extended-release XL version is typically taken in the morning with food.
What is the difference between standard doxazosin and the extended-release Cardura XL?
Standard doxazosin is immediate-release and approved for both high blood pressure and BPH. Cardura XL is an extended-release formula that releases the drug slowly throughout the day. Cardura XL is FDA-approved only for treating BPH, not high blood pressure.
Will doxazosin cause erectile dysfunction?
It is unlikely. Studies generally show that doxazosin does not cause ED. In fact, by improving urinary symptoms, some men find that their quality of life improves. If you experience sexual health changes, they are often related to underlying conditions rather than the drug itself.
Can women safely take this drug?
Yes. While it is most commonly used for prostate care, women may be prescribed doxazosin for high blood pressure or for certain bladder issues or Raynaud’s phenomenon.
Can I take erectile dysfunction drugs like Viagra or Cialis while on this medication?
It’s generally accepted that you should only do this under strict medical supervision. Both drug classes lower blood pressure, and combining them can cause severe dizziness or fainting. Your doctor may need to adjust the timing of your doses.
Does doxazosin interact with blood pressure pills?
Yes. Since doxazosin lowers blood pressure, taking it with other antihypertensives can lead to blood pressure that is too low. Your doctor will monitor your readings closely if you are on multiple medications.
Does this drug cause fluid retention in the ankles and legs?
It can. Swelling (edema) is a known but less common side effect of alpha blockers. If the swelling is uncomfortable or accompanied by weight gain, it’s generally advised to notify your provider.
Can I drink alcohol while taking doxazosin?
Standard guidelines advise caution. Alcohol also relaxes blood vessels and can worsen the dizziness or lightheadedness caused by the medication.
Why did my doctor prescribe this instead of tamsulosin?
Tamsulosin (Flomax) is more selective for the bladder and prostate and doesn’t affect blood pressure as much. Doxazosin is often chosen if a patient needs help with both their prostate symptoms and their blood pressure management.
Comparable Medications
Terazosin, Prazosin, Tamsulosin, or Finasteride?
Your doctor may recommend an alternative medication to Doxazosin if there’s concern for severe side effects or drug interactions.
Terazosin Capsules
From $24.99
This is an older alpha blocker that’s similar to doxazosin. Like doxazosin, it treats both high blood pressure and BPH and requires a slow dose increase to prevent fainting.
Prazosin Capsules
From $27.99
This alpha blocker is more commonly used for high blood pressure. It has a shorter half-life than doxazosin and usually requires multiple daily doses.
Tamsulosin
From $24.99
Tamsulosin is a uroselective alpha blocker. It targets the prostate and has less of an effect on blood pressure. It is often preferred for men who have normal blood pressure but severe BPH symptoms.
Alfuzosin
Similar to tamsulosin, this is a uroselective blocker taken once daily. It generally carries a lower risk of certain sexual side effects compared to other alpha blockers.
Finasteride
From $24.99
Unlike doxazosin, which relaxes muscles, finasteride is a 5-alpha-reductase inhibitor that shrinks the prostate over several months. Doctors often prescribe doxazosin for quick relief and finasteride for long-term management.
Amlodipine
From $24.99
A calcium channel blocker used to lower blood pressure. It does not help with prostate symptoms. Doxazosin is an alternative for patients who cannot tolerate amlodipine or who need the added prostate benefits.
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Important: Information on this page is for educational purposes only. Prescribing decisions are made by independent, licensed providers. TelyRx operates technology-enabled pharmacies and a telehealth platform that connects patients with board-certified licensed providers. Prescriptions, when provider-approved and issued, are filled and shipped by TelyRx-affiliated pharmacies. We do not employ physicians or make prescribing decisions. Learn more about our editorial standards here.