Reviewed on 3/22/2022

What Is Silodosin and How Does It Work?

Silodosin is a prescription medication used to improve urination in men with benign prostatic hyperplasia (enlarged prostate).

  • Silodosin is available under the following different brand names: Rapaflo

What Are Dosages of Silodosin?

Adult dosage


  • 4mg
  • 8mg

Benign Prostatic Hyperplasia

Adult dosage

  • 8 mg orally once daily

Dosage Considerations – Should be Given as Follows: 

  • See “Dosages”

What Are Side Effects Associated with Using Silodosin?

Common side effects of Silodosin include:

Serious side effects of Silodosin include:

  • severe dizziness or fainting,
  • orthostatic hypotension,
  • signs of an allergic reaction: hives, difficult breathing, swelling of the face, lips, tongue, or throat.

Rare side effects of Silodosin include:

  • none 
This is not a complete list of side effects and other serious side effects or health problems that may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

What Other Drugs Interact with Silodosin?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

Silodosin has severe interactions with the following drugs:

Silodosin has serious interactions with at least 80 other drugs.

Silodosin has moderate interactions with at least 136 other drugs.

Silodosin has minor interactions with the following drugs:

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns.


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What Are Warnings and Precautions for Silodosin?


  • Hypersensitivity
  • Severe renal impairment (CrCl less than 30 mL/min)
  • Severe hepatic impairment (Child-Pugh score above 10)
  • Concomitant strong CYP3A4 inhibitors or P-glycoprotein inhibitors

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Silodosin?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Silodosin?”


  • Use with caution in the elderly (risk of hypotension)
  • Not indicated for use in women or children
  • Not for use as hypertensive
  • Postural hypotension, with or without symptoms (e.g., dizziness) may develop when initiating treatment; there is potential for syncope; patients should be cautioned about driving, operating machinery, or performing hazardous tasks when initiating therapy
  • The dose should be reduced to 4 mg in patients with moderate renal impairment; exercise caution and monitor such patients for adverse events
  • Not tested in patients with severe hepatic impairment, and therefore, should not be prescribed to such patients; use with caution in patients with mild-to-moderate hepatic impairment
  • Patients planning cataract surgery should be told to inform their ophthalmologist that they are receiving this therapy; intraoperative floppy iris syndrome observed during cataract surgery in some patients on alpha-1 blockers or previously treated with alpha-1 blockers; variant of small pupil syndrome is characterized by a combination of a flaccid iris that billows in response to intraoperative irrigation currents; progressive intraoperative miosis despite preoperative dilation with standard mydriatic drugs; and potential prolapse of the iris toward phacoemulsification incisions
  • Carcinoma of the prostate and BPH cause many of the same symptoms; these two diseases frequently co-exist; patients thought to have BPH should be examined before starting therapy to rule out the presence of carcinoma of the prostate
  • Drug interaction overview
    • The pharmacodynamic interactions between silodosin and other alpha-blockers have not been determined; the drug should not be used in combination with other alpha-blockers
    • Specific pharmacodynamic interaction study between this drug and antihypertensive agents not performed; patients in Phase 3 clinical studies taking concomitant antihypertensive medications did not experience a significant increase in the incidence of syncope, dizziness, or orthostasis; exercise caution during concomitant use with antihypertensives and monitor patients for possible adverse events
    • Caution is also advised when alpha-adrenergic blocking agents are coadministered with PDE5 inhibitors; alpha-adrenergic blockers and PDE5 inhibitors are both vasodilators that can lower blood pressure; concomitant use of two drug classes can potentially cause symptomatic hypotension

Pregnancy and Lactation

  • Therapy is not indicated for use in females
  • Infertility
    • Males: Possible effects on male fertility could be observed based on findings in rats at exposures that were at least two times higher than at the MRHD (based on AUC); these findings may be reversible; clinical relevance is unknown
  • Lactation
    • Therapy is not indicated for use in females 
Medscape. Silodosin.

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