Flomax Side Effects

Generic Name: tamsulosin

Note: This page contains information about the side effects of tamsulosin. Some of the dosage forms included on this document may not apply to the brand name Flomax.

Not all side effects for Flomax may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to tamsulosin: oral capsule

In addition to its needed effects, some unwanted effects may be caused by tamsulosin (the active ingredient contained in Flomax). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking tamsulosin:

More common
  • Cough or hoarseness
  • fever or chills
  • lower back or side pain
  • painful or difficult urination
Less common
  • Chest pain
  • Dizziness or lightheadedness
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
  • fainting
  • feeling of constant movement of self or surroundings
  • painful or prolonged erection of the penis
  • sensation of spinning
Incidence not known
  • Blistering, peeling, or loosening of the skin
  • blurred vision
  • confusion
  • diarrhea
  • difficult or labored breathing
  • fast, pounding, or irregular heartbeat or pulse
  • itching
  • joint or muscle pain
  • large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs
  • red skin lesions, often with a purple center
  • red, irritated eyes
  • sore throat
  • sores, ulcers, or white spots in the mouth or on the lips
  • sweating
  • tightness of the chest
  • unusual tiredness or weakness

Some of the side effects that can occur with tamsulosin may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • Abnormal ejaculation
  • back pain
  • body aches or pain
  • congestion
  • headache
  • lack or loss of strength
  • sneezing
  • stuffy or runny nose
  • tender, swollen glands in the neck
  • trouble swallowing
  • voice changes
Less common
  • Decreased interest in sexual intercourse
  • decreased sexual drive or performance
  • drowsiness
  • inability to have or keep an erection
  • increased cough
  • loss in sexual ability, desire, drive, or performance
  • nausea
  • pain or tenderness around the eyes and cheekbones
  • sleepiness or unusual drowsiness
  • tooth disorder
  • trouble sleeping
Incidence not known
  • Constipation
  • hives or welts
  • redness of the skin
  • skin rash
  • vomiting

For Healthcare Professionals

Applies to tamsulosin: oral capsule

Nervous system

In one case report, seizure frequency increased in a patient with medial temporal lobe seizures following initiation of tamsulosin (the active ingredient contained in Flomax) treatment. Prior to the use of tamsulosin, the patient experienced 3 to 4 seizures per year. In the first 3 months after starting tamsulosin, seizures were appearing twice a month and by the fourth month of treatment the patient had 3 seizures in one day. Following withdrawal of tamsulosin, seizure frequency returned to baseline.

Nervous system side effects are among the most common and include headache in 4% to 20%, asthenia in 1% to 8%, dizziness in 5% to 15%, somnolence in 0% to 4%, and insomnia in 1% to 2% of patients. (These side effects were also noted among patients treated with placebo in controlled trials, but occurred more often among patients treated with tamsulosin.) According to one case report, tamsulosin caused exacerbation of seizures in a patient with a history of seizures.


Abnormal ejaculation includes ejaculation failure, ejaculation disorder, retrograde ejaculation and ejaculation decrease. In controlled studies, abnormal ejaculation was associated with the use of tamsulosin (the active ingredient contained in Flomax) and was dose-related. The results of one study suggest that intermittent use of tamsulosin may allow for improvement in abnormal ejaculation.

Genitourinary complaints include abnormal (retrograde or decreased volume) ejaculation among 8% (0.4 mg) to 18% (0.8 mg) of male patients. The occurrence of abnormal ejaculation among males who were given placebo in controlled trials averaged 0.2%. Other genitourinary side effects have included impotence (2.9%) and rare cases of urinary retention and priapism.


Respiratory system side effects include rhinitis in 1% to 18%, pharyngitis in 5%, increased cough in 4%, and sinusitis in 3% of patients. In controlled studies, these side effects were also noted in similar but slightly lower incidences among patients who were treated with placebo.


Musculoskeletal complaints--back or chest pains--were reported among 4% to 8% of patients in controlled trials, compared with 4% to 7% among patients who were treated with placebo.


Rarely, flushing and tachycardia have been associated with the use of tamsulosin (the active ingredient contained in Flomax)

Cardiovascular side effects including rare occurrences of orthostatic hypotension have been reported. In two US studies, symptomatic postural hypotension was reported by 0.2% (0.4 mg), 0.4% (0.8 mg), and 0% (placebo) of patients. Syncope was reported by 0.2%, 0.4%, and 0.6% of patients in the above groups, respectively. Because of the risk of syncope, it is recommended that patients be warned against situations where injury could result were syncope to occur.


Gastrointestinal side effects include diarrhea in 5% and nausea in 3% of patients. In controlled studies, these side effects were also noted in similar but slightly lower incidences among patients who were treated with placebo. Rarely, constipation, gastric pain, dysphagia, and anorexia have been associated with the use of tamsulosin (the active ingredient contained in Flomax)


Although the overall prevalence of intraoperative floppy iris syndrome (IFIS) is 1% to 2%, the incidence of IFIS associated with the use of tamsulosin (the active ingredient contained in Flomax) ranges from 43% to 63%. Most reports were in patients treated with an alpha-1 blocker at the time IFIS occurred, but in some instances the alpha-1 blocker had been stopped prior to surgery. The manufacturer recommends that male patients be questioned to determine whether or not they have taken tamsulosin or other alpha-1 blockers prior to being considered for cataract surgery. If it is determined that the patient has taken an alpha-rt1 blocker, the patient's ophthalmologist should be prepared for possible modifications to their surgical technique that may be necessary should IFIS be observed during the procedure.

Clinical studies in men 66 years of age and older who were exposed to tamsulosin within 14 days of cataract surgery was significantly associated with serious postoperative ophthalmic adverse events other than IFIS.

Ocular side effects including amblyopia have been reported in 0.2% of men given 0.4 mg, 2% of men given 0.8 mg, and in 0.4% of men who were given placebo.

Intraoperative Floppy Iris Syndrome (IFIS) has been observed in some patients undergoing phacoemulsification cataract surgery while being treated with alpha-1 blockers including tamsulosin.


General side effects unrelated to a particular organ system include a flu-like syndrome or infection in approximately 2% of patients. (Similar incidences were observed among patients who were treated with placebo in controlled trials.)

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