Flomax side effects can include dizziness, runny nose, and issues with ejaculation. While more serious side effects are rare, they can include low blood pressure and painful erection, among others.

Flomax, also known by its generic name tamsulosin, is an alpha-adrenergic blocker. It’s approved by the U.S. Food and Drug Administration (FDA) to help improve urine flow in men who have benign prostatic hyperplasia (BPH).

BPH is an enlargement of the prostate that’s not caused by cancer. It’s fairly common among older men. Sometimes, the prostate becomes so large that it obstructs the flow of urine. Flomax works by relaxing the muscles in the bladder and prostate, which leads to improved flow of urine and fewer symptoms of BPH.

Like all medications, Flomax comes with the potential for side effects. The most common side effects include dizziness, runny nose, and abnormal ejaculation, including:

  • failure to ejaculate
  • decreased ease of ejaculation
  • ejaculation of semen into the bladder instead of out of the body

Serious side effects are rare. If you take Flomax and think you’re experiencing one of the following serious side effects, see a doctor right away or call 911.

Orthostatic hypotension

This is low blood pressure that happens when you stand up. It can cause lightheadedness, dizziness, and fainting. This effect is more common when you first start taking Flomax. It’s also more common if your doctor changes your dosage. You should avoid driving, operating machinery, or doing similar activities until you know how your dosage of Flomax affects you.


This is a painful erection that won’t go away and that’s not relieved by having sex. Priapism is a rare but severe side effect of Flomax. If you experience priapism, contact your doctor immediately. Untreated priapism can lead to permanent problems with having and maintaining an erection.

Read more: Symptoms, treatment, and outlook for priapism »

Allergic reaction

An allergic reaction to Flomax can include rash, itching, hives, trouble breathing, and swelling of your throat or tongue.

Serious skin reactions

Flomax can cause serious skin reactions, including Stevens-Johnson syndrome. Symptoms of skin reactions can include raised welts, facial swelling, fever, and difficulty breathing.

Intraoperative floppy iris syndrome

This is a complication during surgery for cataracts or glaucoma. Although rare, this complication has been reported by people who have used Flomax and also had these surgeries. Tell your doctor or surgeon that you take Flomax if you need to have cataract or glaucoma surgery.

Flomax is only approved by the FDA for use in men to treat BPH. However, research has indicated that Flomax is also an effective treatment for women who have trouble emptying their bladders. It can also help both men and women pass kidney stones. Therefore, some doctors also prescribe Flomax off-label for men and women as treatment for kidney stones and urination trouble.

Because Flomax isn’t FDA approved for use in women, the side effects of this drug in women have not been studied. However, women who have used this drug report similar side effects to those in men, with the exceptions of priapism and abnormal ejaculation.

Other drugs can be used to help relieve symptoms of BPH. Two such drugs are Uroxatral and Avodart.


Uroxatral is the brand name for the drug alfuzosin. Like Flomax, this drug is also an alpha-adrenergic blocker. However, runny nose and abnormal ejaculation are not common with this drug. It can cause dizziness, headaches, and tiredness. Serious side effects of Uroxatral include:

  • serious skin reactions, such as peeling
  • allergic reactions
  • orthostatic hypotension
  • priapism


Avodart is the brand name for the drug dutasteride. It’s in a class of drugs called 5-alpha reductase inhibitors. It affects hormones like testosterone and actually shrinks your enlarged prostate. The most common side effects of this drug include:

  • impotence, or trouble getting or keeping an erection
  • decrease sex drive
  • ejaculation problems
  • enlarged or painful breasts

Some serious side effects of this drug include allergic reactions and skin reactions such as peeling. You may also have a higher chance of developing a severe form of prostate cancer that grows rapidly and is difficult to treat.

Flomax may cause side effects. Some of these are similar to side effects of other drugs used to relieve symptoms of BPH. While side effects are an important concern when selecting a treatment, there are other considerations as well. Talk to your doctor. They can tell you about other important factors, such as possible drug interactions or other medical conditions that you have, that go into deciding your treatment.