Tamsulosin dosage: what’s right for me?

Tamsulosin is available in generic form or as the brand name medication Flomax. It is prescribed for benign prostatic hyperplasia (BPH), more popularly—and infamously—known as an enlarged prostate.

Always follow your healthcare provider's advice about taking tamsulosin. Below are the general recommendations regarding tamsulosin dosage.

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The recommended starting dose of tamsulosin (or tamsulosin hydrochloride) is 0.4 mg once a day. It should be taken 30 minutes after the same meal each day. Tamsulosin should be swallowed whole. Don't crush, chew, or open tamsulosin capsules. If tamsulosin 0.4 mg doesn't work for you after two to four weeks of consistent use, your healthcare provider might increase your dosage (DailyMed, 2020)

Suppose you need to discontinue tamsulosin for several days. In that case, your healthcare provider will likely restart you at the 0.4 mg dose, regardless of whether you had been taking a higher dose before stopping (DailyMed, 2020). You may experience significant low blood pressure (hypotension) when you begin retaking the medication, which is why it is usually restarted at the lowest dose.

You should store tamsulosin at room temperature and not in areas with high heat or moisture (like the bathroom). In the event of a missed dose, take the medication as soon as possible, unless it's almost time for your next dose. In that case, take the next dose as scheduled. Never take two doses of tamsulosin at once (MedlinePlus, 2018).

Most prescription plans cover tamsulosin. The cost of a 30-day supply ranges between $9 to $35 (GoodRx, n.d.).

Tamsulosin is used to treat the symptoms of benign prostatic hyperplasia (BPH), commonly known as an enlarged prostate. BPH can cause urinary retention and other potentially uncomfortable symptoms.

Tamsulosin is part of a class of drugs known as alpha-blockers. It relaxes muscles in the prostate and bladder. This relaxation improves both the flow of urine and BPH symptoms.

Tamsulosin is also prescribed "off-label" for (UpToDate, n.d.):

• chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) 

• kidney stones in the urethra—by relaxing urethra muscles, tamsulosin can help dislodge those stones, allowing them to pass during urination

As men age, the prostate naturally increases in size. For some men, this can put pressure on the urethra and bladder, partially obstructing the flow of urine and causing symptoms. 

Common symptoms of BPH include:

• Greater need to urinate

• Frequent nighttime urination

• Difficulty urinating 

• Straining while urinating

• Frequent starting and stopping of urination

• Weak urine stream

• Trouble starting urination

BPH is a common condition. Experts estimate that about half of all men between the ages of 51 and 60 are affected by BPH (AUA, 2020). In men older than 60, that number rises to above 70 percent and 90 percent in men over age 80 (Narayan, 2005; AUA, 2020). Since BPH and prostate cancer often exist together, talk to your healthcare provider about prostate cancer screening before starting treatment and at regular intervals afterward.

Urinary retention is the inability to empty your bladder fully; it's often caused by BPH. Urinary retention can also be caused by prostatitis (inflammation of the prostate), urinary tract infections, urinary stones, and scars or tumors that block urine outflow (NIDDK, 2019).

Tamsulosin works by relaxing the smooth muscles in the prostate and bladder, making urination easier.

Studies indicate that tamsulosin is generally safe and well-tolerated for long-term use (Narayan, 2005). However, like all medications, you might experience side effects while on tamsulosin, which can range from mild to severe. These side effects include (DailyMed, 2020):

• Orthostatic hypotension: low blood pressure and symptoms of dizziness/lightheadedness or fainting (syncope) when standing up after sitting. This is more likely to occur after taking your first dose or an increased dose.

• Headache

• Dizziness

• Abnormal ejaculation, including retrograde ejaculation 

• Runny nose or stuffy nose (rhinitis)

• Drowsiness

• Diarrhea

• Nausea

• Back pain

• Chest pain

• Intraoperative floppy iris syndrome (IFIS), a complication during cataract surgery or glaucoma surgery

• Priapism, a painful erection lasting four or more hours

Tell your healthcare provider about any other drugs you're taking before starting tamsulosin, including prescription drugs, over-the-counter medications, and supplements. Potential drug interactions with tamsulosin include (DailyMed, 2020):

CYP3A4 and CYP2D6 inhibitors 

CYP3A4 and CYP2D6 are two enzymes that help the liver metabolize tamsulosin. Any drug that blocks or inhibits CYP3A4 and CYP2D6 can increase the concentration of tamsulosin in the body. Examples include cimetidine, ketoconazole, erythromycin, terbinafine, and paroxetine. If you're taking those drugs, your healthcare provider may adjust your dose of tamsulosin to avoid potential adverse effects.

PDE5 inhibitors 

Phosphodiesterase-5 (PDE5) inhibitors are oral medications commonly used to treat erectile dysfunction (ED). They include sildenafil (brand name Viagra; see Important Safety Information), tadalafil (brand name Cialis; see Important Safety Information), vardenafil (brand name Levitra), and avanafil (brand name Stendra). Like tamsulosin, PDE5 inhibitors work by dilating blood vessels to improve blood flow into the penis. This also has the effect of lowering your blood pressure. Therefore, taking both tamsulosin and PDE5 inhibitors may cause your blood pressure to drop too low (hypotension). 

This is not a complete list. Talk to your healthcare provider or pharmacist for more information about potential drug interactions with tamsulosin.

People with certain medical conditions should be careful when using tamsulosin or even avoid it altogether. Tamsulosin is not approved for use in women. Consult with your healthcare provider for additional information. 

People with low blood pressure

Since one of the side effects of tamsulosin is a drop in blood pressure, use tamsulosin with caution if you have low blood pressure or positional blood pressure changes, like orthostatic hypotension. Tamsulosin could potentially worsen already low pressures, especially after starting or increasing your dose.

People who have cataracts or glaucoma 

Tamsulosin may affect your iris, leading to intraoperative floppy iris syndrome (IFIS) that may be noted during cataract surgery or glaucoma surgery. Avoid starting tamsulosin if you're planning to have cataract or glaucoma surgery. Tell your healthcare provider if you've taken tamsulosin in the months preceding any scheduled surgery; IFIS has occurred even when tamsulosin was discontinued months before those eye procedures.

People with heart failure

Tamsulosin may worsen existing heart failure.

People with sulfa allergies

Some people who are allergic to drugs in the sulfonamide (sulfa) class may also have an allergic reaction to tamsulosin (e.g., skin rash, swelling, trouble breathing, etc.). If you are allergic to sulfa drugs, make sure your healthcare provider knows about it, and use tamsulosin with caution. 

This list does not include all tamsulosin warnings. Seek medical advice from your healthcare provider or pharmacist for more drug information.

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Current version

November 11, 2020

Written by

Michael Martin

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.