Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where this enzyme works.

Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. When a man is sexually stimulated, his body's normal response is to increase blood flow to his penis to produce an erection. By controlling the enzyme, sildenafil helps to maintain an erection after the penis is stroked. Without physical action to the penis, such as that occurring during sexual intercourse, sildenafil will not work to cause an erection.

Sildenafil is also used in both men and women to treat the symptoms of pulmonary arterial hypertension. This is a type of high blood pressure that occurs between the heart and the lungs. When hypertension occurs in the lungs, the heart must work harder to pump enough blood through the lungs. Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. This will increase the supply of blood to the lungs and reduce the workload of the heart.

This medicine is available only with your doctor's prescription.

Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it more often than your doctor ordered. If too much is used, the chance of side effects is increased.

Special patient instructions comes with sildenafil. Read the directions carefully before you start using sildenafil and each time you get a refill of your medicine.

You may take this medicine with or without food.

If you are using the oral liquid, shake the bottle well for at least 10 seconds before measuring each dose. Use the oral syringe provided in the package to measure each dose. Wash the oral syringe after each use.

This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it. It continues to work for up to 4 hours, although its action is usually less after 2 hours.

Use only the brand of this medicine that your doctor prescribed. Different brands may not work the same way.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

Less common

Bladder pain

burning feeling in the chest or stomach

burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings

cloudy or bloody urine

dizziness

increased frequency of urination

indigestion

pain on urination

stomach upset

tenderness in the stomach area

Rare

Abnormal vision

anxiety

behavior change similar to drunkenness

bleeding of the eye

blurred vision

bone pain

breast enlargement

chest pain

chills

cold sweats

confusion

convulsions (seizures)

cool and pale skin

deafness or hearing loss

decrease in amount of urine or the frequency of urination

decreased vision

difficulty in concentrating

dizziness or lightheadedness, especially when getting up suddenly from a lying or sitting position

double vision

drowsiness

dry eyes

dry mouth

dryness, redness, scaling, or peeling of the skin

excessive hunger

eye pain

fainting or faintness

fast, irregular, or pounding heartbeat

feeling of something in the eye

fever or chills

headache (severe or continuing)

increase in the size of the pupil

increased sweating

increased thirst

lower back or side pain

migraine headache

nausea (severe or continuing)

nervousness

nightmares

numbness of the hands

painful, swollen joints

prolonged, painful erection of penis

redness, burning, or swelling of the eyes

redness, itching, or tearing of the eyes

restless sleep

seeing shades of colors differently than before

sensitivity to light

shakiness

skin lesions with swelling

skin paleness

skin rash, hives, or itching

skin ulcers

slurred speech

sore throat

sudden weakness

swelling of the face, hands, feet, or lower legs

trouble breathing

twitching of the muscles

unusual feeling of burning or stinging of the skin

unusual tiredness or weakness

vision changes

vision loss, temporary

Incidence not known

Blindness

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Aches or pains in the muscles

bloody nose

diarrhea

difficult or labored breathing

flushing

headache

pain or tenderness around the eyes and cheekbones

redness of the skin

sneezing

stomach discomfort following meals

stuffy or runny nose

trouble sleeping

unusually warm skin

Rare

Abdominal or stomach pain

abnormal dreams

anxiety

clumsiness or unsteadiness

cough

diarrhea or stomach cramps (severe or continuing)

difficulty in swallowing

ear pain

increased amount of saliva

increased skin sensitivity

lack of coordination

loss of bladder control

mental depression

nausea

numbness or tingling of the hands, legs, or feet

rectal bleeding

redness or irritation of the tongue

redness, soreness, swelling, or bleeding of the gums

ringing or buzzing in the ears

sensation of motion, usually whirling, either of one's self or of one's surroundings

sexual problems in men (continuing), including failure to experience a sexual orgasm

sleepiness

sores in the mouth and on the lips

tense muscles

trembling and shaking

vomiting

waking to urinate at night

worsening of asthma

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

It is important that you tell all of your doctors that you take sildenafil. If you need emergency medical care for a heart problem, it is important that your doctor knows when you last took sildenafil.

Do not use this medicine if you are also using a nitrate medicine, often used to treat angina or high blood pressure. Nitrate medicines include nitroglycerin, isosorbide, Imdur®, Nitro-Bid®, Nitro-Dur®, Nitrol® ointment, Nitrolingual® spray, Nitrostat®, and Transderm Nitro®. Some illegal ("street") drugs called "poppers" (such as amyl nitrate, butyl nitrate, or nitrite). Do not use this medicine if you also use riociguat (Adempas®).

If you will be taking this medicine for pulmonary arterial hypertension, your doctor will want to check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it.

If you take sildenafil for pulmonary arterial hypertension, do not take Viagra® or other PDE5 inhibitors, such as tadalafil (Cialis®) or vardenafil (Levitra®). Viagra® also contains sildenafil. If you take too much sildenafil or take it together with these medicines, the chance for side effects will be higher.

Sildenafil should not be used with any other medicine or device that causes erections.

It is important to tell your doctor about any heart problems you have now or may have had in the past. This medicine can cause serious side effects in patients with heart problems.

If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. This condition may require prompt medical treatment to prevent serious and permanent damage to your penis.

If you experience a sudden loss of vision in one or both eyes, contact your doctor immediately.

Check with your doctor right away if you have a sudden decrease in hearing or loss of hearing, which may be accompanied by dizziness and ringing in the ears.

If you already use medicine for high blood pressure (hypertension), sildenafil could make your blood pressure go too low. Call your doctor right away if you have more than one of these symptoms: blurred vision, confusion, dizziness, faintness, or lightheadedness when getting up from a lying or sitting position suddenly, sweating, or unusual tiredness or weakness.

This medicine does not protect you against sexually transmitted diseases (including HIV or AIDS). Use protective measures and ask your doctor if you have any questions about this.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.