- What is sildenafil, and how does it work (mechanism of action)?
- What brand names are available for sildenafil?
- Is sildenafil available as a generic drug?
- Do I need a prescription for sildenafil?
- What are the side effects of sildenafil?
- What is the dosage for sildenafil?
- Which drugs or supplements interact with sildenafil?
- Is sildenafil safe to take if I'm pregnant or breastfeeding?
- What else should I know about sildenafil?
What is sildenafil, and how does it work (mechanism of action)?
Viagra (sildenafil) is an oral drug that is used for treating impotence (or erectile disfunction, ED, the inability to attain or maintain a penile erection). It is in a class of drugs called phosphodiesterase inhibitors (PDE-5 inhibitors) that also includes
It has been estimated that impotence affects 140 million men worldwide. Over half of all men with impotence are thought to have some physical (medical) cause. The remainder are believed to have psychogenic causes of impotence. Medical causes of impotence include diabetes and circulatory, neurological, or urological conditions.
Penile erection is caused by the engorgement of the penis with blood. This engorgement occurs when the blood vessels delivering blood to the penis increase the delivery of blood and the blood vessels carrying blood away from the penis decrease the removal of blood. Under normal conditions, sexual stimulation leads to the production and release of nitric oxide in the penis. Nitric oxide then activates the enzyme, guanylate cyclase, which causes the production of cyclic guanosine monophosphate (cGMP). It is the cGMP that is primarily responsible for the erection by affecting the amount of blood that the blood vessels deliver and remove from the penis.
Viagra inhibits an enzyme called phosphodiesterase-5 (PDE5) which destroys the cGMP. Thus, Viagra prevents the destruction of cGMP and allows cGMP to accumulate and persist longer. The longer cGMP persists, the more prolonged the engorgement of the penis. The FDA approved Viagra in March 1998.
What are the side effects of sildenafil?
Approximately 15% of persons taking Viagra experience side effects. The most common side effects are:
What is the dosage for sildenafil?
- The usual recommended dose is 25 to 100 mg 1 hour before sexual activity.
- The maximum dose is 100 mg daily.
- The elderly (over 65 years of age) should start at 25 mg before sexual activity.
- Sildenafil is rapidly absorbed. Maximum observed plasma concentrations are reached within 30 to 120 minutes (median 60 minutes) of oral dosing in the fasted state. When sildenafil is taken with a high fat meal, the rate of absorption is reduced, with an average delay in the time to maximal concentration of 1 hour.
Which drugs or supplements interact with sildenafil?
Viagra increases the effects of the blood pressure lowering medications. It also increases the blood pressure lowering effects of nitrates, for example, isosorbide dinitrate (Isordil), isosorbide mononitrate (Imdur, Ismo, Monoket), nitroglycerin (Nitro-Dur, Transderm-Nitro) that are used primarily for treating angina. Patients taking nitrates should not receive Viagra.
Patients should not combine Viagra with other PDE5 inhibitors (for example, vardenafil [Levitra], tadalafil [Cialis]).
Cimetidine (Tagamet), erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox), atazanavir (Reyataz), and mibefradil (Posicor) can cause marked increases in the amount of Viagra in the body. Patients taking these medications should be observed carefully if sildenafil is used.
It is expected that rifampin will decrease blood levels of Viagra and probably reduce its effectiveness.
Latest Sexual Health News
Is sildenafil safe to take if I'm pregnant or breastfeeding?
Although extensive testing in animals has demonstrated no negative effects on the fetus, Viagra has not been studied in pregnant women. There is no effect on sperm count or motility of sperm in men.
It is not known whether sildenafil is excreted into breast milk.
What else should I know about sildenafil?
What preparations of sildenafil are available?
Sildenafil (Viagra) is a blue, film-coated, rounded, diamond-shaped tablet that comes in 25, 50, and 100 mg tablets for treating impotence.
How should I keep sildenafil stored?
Tablets should be kept at room temperature between 15 C and 30 C (59 F and 86 F).
Sildenafil (Viagra) is a medication prescribed for the treatment of impotence (erectile dysfunction, ED) caused by medical or psychological conditions. Side effects, drug interactions, warnings and precautions, and patient safety information should be reviewed prior to taking any medication.
Multimedia: Slideshows, Images & Quizzes
Sex Quiz: Love & Relationships Facts
Relationships, sex, and love! Could it be that what motivates physical attraction in us may be all in our minds? Take the Sex &...
Erectile Dysfunction (Impotence) Quiz: Causes & Treatment
Did you know that certain medical condition may be responsible for ED? Some causes of impotence are medically treatable and...
Picture of Penis
The penis is the male sex organ, reaching its full size during puberty. See a picture of the Penis and learn more about the...
Low Blood Pressure (Hypotension): Symptoms, Signs, Causes
What is low blood pressure (hypotension)? Explore low blood pressure causes, symptoms, and signs. Discover what is considered low...
Sex-Drive Killers: The Causes of Low Libido
Noticing a lack of intimacy with your partner? Here we explore how stress, lack of sleep, weight gain, depression and low T can...
Erectile Dysfunction (ED) Causes and Treatment
Having erection problems? What is erectile dysfunction (ED)? Learn about erectile dysfunction causes and treatments such as drugs...
Screening Tests Every Man Should Have
Getting the right screening test at the right time is one of the most important things a man can do for his health. Learn at what...
Men's Health: Dealing With Body Odor, Sweating, Back Hair, & More
Most men struggle with belly fat, back hair, sweating, erectile dysfunction, gas, body odor, or bad breath at some point. Get...
Men's Health: What Foods Improve Male Health?
What foods have the most health benefits for men? For losing weight, gaining muscle, and lowering your risk of prostate cancer,...
Better Sex After 50
It's never too late to improve your sex life. Learn how to overcome common health conditions affecting those over 50 such as...
Sex Tips for Men: How to Have a Better Sex Life
Learn sex tips for men that lead to more sexual pleasure such as better communication, focusing on pleasurable sensations,...
19 Secrets Women Wish You Knew With Pictures
There are secrets women would love for you to know. These relationship secrets are based on the study of healthy, happy couples,...
For Men Only: 15 Ways to Stay On Top of Your Game
See how first impressions, staying active, good hygiene and more lifestyle tips can improve your overall health and well-being....
Related Disease Conditions
Erectile Dysfunction (ED, Impotence)
Erectile dysfunction (ED, impotence) is the failure to achieve or maintain an erection. There are many potential underlying...
Scleroderma is an autoimmune disease of the connective tissue. It is characterized by the formation of scar tissue (fibrosis) in...
Pulmonary Hypertension (Symptoms, Treatment Medications, Life Expectancy)
Pulmonary hypertension is an increase pressure in the pulmonary arteries that carry blood from the lungs to the heart. The most...
Men's health is an important component to a happy lifestyle and healthy relationships. Eating healthy, exercise, managing stress,...
Enjoying a satisfying sex life as we age is important to both physical and mental health. As we age, diseases and conditions may...
Peyronie's Disease (Curvature of the Penis)
Peyronie's disease or curvature of the penis (Peyronie disease) is a condition in which scar tissue develops inside the penis....
Sexual health information including birth control, impotence, herpes, sexually transmitted diseases, staying healthy, women's...
Sexual Problems (Sex) in Women
Sexual dysfunction refers to a problem that arises during any phase of the sexual response cycle, preventing an individual or...
Sexual Problems in Men
Male sexual dysfunction can be caused by physical or psychological problems. Common sexual problems in men include erectile...
Night Sweats (In Men and Women) Causes, Remedies, and Treatments
Night sweats are severe hot flashes that occur at night and result in a drenching sweat. The causes of night sweats in most...
Sex, Urinary, and Bladder Problems of Diabetes
Having diabetes can mean early onset and increased severity of bladder symptoms (urinary incontinence and urinary tract...
Multiple Sclerosis Early Symptoms and Signs (Early, Body Areas Affected)
Multiple sclerosis (MS) symptoms vary from person to person, and can last for days to months without periods of remission....
Treatment & Diagnosis
- Sex & Love FAQs
- Impotence Erectile Dysfunction FAQs
- 8 Natural Remedies for Erectile Dysfunction
- Medication Disposal
- Dangers of Mixing Medications
- Viagra: The Little Blue Pill That Could
- Drugs: The Most Common Medication Errors
- Erectile Dysfunction Drugs: Drug Interactions
- How To Reduce Your Medication Costs
- Pharmacy Visit, How To Get The Most Out of Your Visit
- Indications for Drugs: Approved vs. Non-approved
- Radio ID Tags For US Drugs (RFID)
- Viagra - Impotence Treatment Update
- Viagra and Nitrates Don't Mix
- Drugs: Buying Prescription Drugs Online Safely
- Grapefruit Juice and Drug Interactions
- Things You Should Know About the Penis
- Generic Drugs, Are They as Good as Brand-Names?
Medications & Supplements
Prevention & Wellness
- Some E-Cig Liquids Contain Erectile Dysfunction Drugs: FDA
- Guys, Avoid 'Rhino' Sexual Enhancement Products, FDA Says
- Viagra Linked to Trouble With Color Vision: Report
- Good News, Guys: Viagra Prices Start to Tumble Today
- Viagra Won't Help, and May Harm, Patients With a Heart Valve Disorder
- Impotence Meds Might Give Men's Hearts a Boost, Too
- Impotence Drugs Won't Raise Melanoma Risk, Study Suggests
- Recalled Supplements Linger on U.S. Store Shelves, Study Finds
- Illegal Online Meds Targeted in Worldwide Crackdown, FDA Says
- Erectile Dysfunction Tied to Long-Term Narcotic Use in Men
- Viagra, Aliskiren Not Helpful for Heart Failure After All: Studies
- Adding Testosterone to Viagra May Not Help Erectile Dysfunction
- Viagra Can Help Prostate Cancer Patients Maintain Sex Lives: Study
- Active Ingredient in Viagra Shrunk Disfiguring Growths in Kids
- 'Female Viagra' Is Rejected by FDA Panel
Health Solutions From Our Sponsors
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
FDA Prescribing Information.