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Sildenafil Overview

Sildenafil citrate is a generic drug that is widely available under the brand name Viagra. It belongs to a class of medications known as phosphodiesterase type 5 (PDE5) inhibitors. 

Examples of PDE5 inhibitors include

• Sildenafil (brand names Viagra, Revatio)

• Tadalafil (brand names Cialis, Adcirca)

• Vardenafil (brand names Levitra and Staxyn)

• Avanafil (brand name Stendra)

Learn more: “Viagra Vs. Cialis: What’s More Effective?”

Common Uses of Sildenafil

Sildenafil citrate (Viagra) is approved by the U.S. Food and Drug Administration (FDA) to treat erectile dysfunction. 

Sildenafil is also FDA-approved and available under the trade name Revatio for the treatment of a condition called pulmonary arterial hypertension (PAH) or high blood pressure in the lungs. 

How Sildenafil Works

Sildenafil works by blocking the action of an enzyme called phosphodiesterase type-5 (PDE-5) or, more specifically, cGMP-specific phosphodiesterase type-5. Cyclic guanosine monophosphate (cGMP) is a substance that induces the relaxation of smooth muscle (which is favorable for achieving and maintaining an erection). 

In other words, sildenafil and other drugs in this class prevent the breakdown of cGMP by blocking the PDE-5 enzyme. Increased levels of cGMP allow smooth muscle relaxation, thus promoting blood flow to the penis to achieve and sustain an erection in response to sexual arousals.

Is It Okay To Take Sildenafil Everyday?

It is generally okay to take sildenafil every day, but it should not be taken more than once every 24 hours. You should check with your doctor to make sure it is safe to use sildenafil every day. 

Does Sildenafil Make You "Rock Hard"?

Sildenafil (Viagra) is effective at helping people with ED to achieve and maintain an erection. However, this medication only works in the presence of sexual arousal or stimulation. In other words, Viagra does not work to increase your sex drive or libido. It's important to remember that your doctor is there to support you. If there has been a significant change in your sex drive that affects your personal life without apparent causes, such as stress, job issues, or the loss of a loved one, don't hesitate to talk to your doctor. 

Find Savings On Erectile Dysfunction Medications

Side Effects of Sildenafil

Mild vs Severe Side Effects

Mild side effects of sildenafil do not require medical attention. They typically go away once your body adjusts to the medicine. However, you should tell your doctor if these adverse effects are severe or persistent.

Serious side effects of sildenafil can be life-threatening and require emergency medical attention.

Frequently Reported Sildenafil Side Effects

The most common side effects of sildenafil citrate are as follows:

• Headache pain (16-28% of patients)

• Flushing (10-19% of patients)

• Dyspepsia (indigestion or upset stomach) (3-17% of patients)

• Abnormal vision (color tint, blurred vision, increased light sensitivity) (1-11% of patients)

• Nasal congestion (4-9% of patients)

• Back pain and muscle aches (2-4% of patients)

• Dizziness (3-4% of patients)

• Nausea (2-3% of patients)

• Skin sensitivity or rash (1-3% of patients)

Does Sildenafil Have Serious Side Effects?

Yes, in a small number of people, sildenafil can cause serious side effects, including heart attack, heart failure, vision difficulty, hearing loss, priapism (prolonged, painful erection), and severe allergic reactions. 

Serious Reactions to Sildenafil: Risk Factors and Immediate Actions to Take

Cardiovascular Risks

Men with pre-existing cardiovascular disease can experience cardiac events during or after sexual activity. The use of sildenafil to treat erectile dysfunction is not advisable in men who have been recommended to refrain from sexual activity due to their cardiovascular status.

The vasodilatory (blood vessel widening) effects of sildenafil can cause a temporary decrease in blood pressure in the lying position. This is not concerning in most men. However, low blood pressure can be concerning in men with underlying cardiovascular problems, especially in combination with sexual activity.

People with the following heart conditions should consult their doctor before taking a sildenafil tablet:

• Left ventricular outflow obstruction (aortic stenosis or idiopathic hypertrophic subaortic stenosis).

• Congestive heart failure or heart disease resulting in unstable angina.

• Severe impairment of autonomic blood pressure control.

• Myocardial infarction (heart attack), stroke, or life-threatening cardiac arrhythmia in the last 6 months.

• Resting hypotension (blood pressure below 90/50 mmHg) or hypertension (blood pressure above 170/110 mmHg).

Priapism (Prolonged Erection)

Rarely, sildenafil can cause a prolonged, painful erection lasting more than 4 hours. This is a medical emergency and can result in permanent damage to the penile tissues without timely treatment. Risk factors for priapism include structural deformities of the penis (angulation, cavernosal fibrosis, Peyronie disease), sickle cell anemia, multiple myeloma, and leukemia. 

Eye Problems

There are reports of sudden vision loss in a small number of patients who took PDE5 inhibitors, including sildenafil. Stop taking sildenafil and seek emergency medical attention if you develop vision loss in one or both eyes. This can be a sign of a rare condition called non-arteritic anterior ischemic optic neuropathy (NAION), which can result in decreased vision and permanent vision loss. Risk factors for NAION include a “crowded” optic disc and prior episodes of NAION. Sildenafil should also be used with caution in people with eye conditions such as retinitis pigmentosa.

Hearing Loss

Rarely have people developed a sudden decrease in hearing or complete loss of hearing after taking a sildenafil tablet. Stop taking sildenafil tablets and seek immediate medical attention if this happens. The hearing loss may be accompanied by tinnitus (ringing in the ears) and dizziness.

Drug Interactions

Sildenafil should be used with caution in people taking a class of drugs called alpha-blockers. PDE5 inhibitors such as sildenafil and alpha-adrenergic blockers are both vasodilators that cause the widening of the blood vessels and lower blood pressure. When used in combination, the additive effect can result in dangerously low blood pressure. Call your doctor immediately or seek emergency medical care for symptoms of hypotension such as lightheadedness, dizziness, or fainting. These symptoms are especially likely when going from a lying or sitting position to standing.

Other antihypertensive drugs, such as amlodipine, have vasodilatory properties and can also cause a lowering of blood pressure when used in combination with PDE5 inhibitors. 

Concomitant use of an HIV medication (protease inhibitor) called ritonavir can significantly increase the blood concentration of sildenafil, thereby increasing the risk of sildenafil adverse effects such as low blood pressure, fainting and prolonged erection. If you are taking ritonavir, your doctor may prescribe a lower dose of sildenafil.

Combining sildenafil and other PDE5 inhibitors with other treatments for pulmonary arterial hypertension (PAH) is not recommended due to an increased risk of significantly low blood pressure.

Bleeding Risk

There are postmarketing reports of bleeding events in people who took sildenafil tablets. A direct cause-and-effect relationship has not been established, but this medication should be used with caution in people with bleeding disorders and actively bleeding peptic ulcers.

Sexually Transmitted Diseases

Taking sildenafil does not protect against sexually transmitted diseases, including human immunodeficiency virus (HIV). You should continue to take precautions to guard against sexually transmitted infections (STIs).

Learn more: “How Is HIV Transmitted? Tips for Prevention.”

Serious Allergic Reactions

Rarely, sildenafil can cause a severe allergic reaction, including anaphylaxis (throat closing and difficulty breathing). Seek emergency medical care if you develop a skin rash, itching, hives, swelling, or trouble breathing after taking a sildenafil tablet. 

Precautions and Interactions: What Should You Avoid When Taking Sildenafil?

The following precautions are essential to ensure safety while using sildenafil:

• Do not take sildenafil if you have been advised to avoid sexual activity due to your cardiovascular status.

• Seek emergency treatment if your erection lasts more than 4 hours. 

• Seek immediate medical care if you develop sudden loss of vision or sudden hearing loss after taking sildenafil. 

• Talk to your healthcare professional about drinking grapefruit juice while on sildenafil. Grapefruit juice can increase the amount of sildenafil absorbed by your body, causing you to experience more severe side effects.

• Avoid eating a high-fat meal if you plan to take sildenafil. This can block the absorption of the drug and make it less effective.

• Avoid drinking alcohol while taking sildenafil. Alcohol can make erectile dysfunction symptoms worse and increase the risk of side effects such as dizziness on sildenafil.

• Avoid using recreational drugs such as amyl nitrate (commonly known as poppers). Combining amyl nitrate with sildenafil can result in a dangerous drop in blood pressure.

Medical History and Follow-Up

Before starting sildenafil therapy, it’s important to discuss your medical history thoroughly with your healthcare professional. Be sure to mention health conditions such as heart disease, cardiovascular problems, eye or ear problems, episodes of priapism (prolonged, painful erection), and serious allergic reactions or drug reactions.

Keep all your medical and laboratory appointments during sildenafil therapy. Tell your doctor how the medication is working. Report common sildenafil side effects to your healthcare provider if they are severe or persistent. Your healthcare provider may adjust your sildenafil dose, switch you to a different medication, or prescribe other medications to minimize sildenafil side effects.

Medications to Avoid When Taking Sildenafil

Give your healthcare professional a complete list of your medications, including prescription drugs, over-the-counter medications, dietary supplements, and herbal products, to avoid drug interactions between sildenafil and your other medications. Interactions between sildenafil and certain other medications can increase the risk of serious side effects. Talk to your doctor before taking sildenafil if you are on medications such as:

• Nitrates used to treat chest pain, for example, isosorbide mononitrate (Monoket), isosorbide dinitrate (Isordil), and nitroglycerin (Nitro-Dur, Nitrostat, Nitromist)

• Certain blood pressure medications, such as amlodipine

• Alpha-blockers such as doxazosin are prescribed for high blood pressure and benign prostatic hyperplasia (BPH)

• Some antifungal agents such as itraconazole and ketoconazole.

• Certain HIV/AIDS medicines, such as ritonavir

• Riociguat, a medication used to treat pulmonary arterial hypertension (PAH)

Note: This is not a complete list of interactions between sildenafil and other drugs. 

Other ED Treatments

Sildenafil is commonly used to treat ED, but other treatment options are available for people who cannot take this medication. Talk to your doctor about other oral medications for erectile dysfunction, vacuum erection devices, penile implants, and lifestyle modifications. 

When to Seek Medical Attention?

Call your doctor immediately or seek emergency medical attention if you experience severe sildenafil side effects such as:

• Severe chest pain 

• Priapism (prolonged and painful erection)

• Sudden vision changes 

• Sudden decrease in hearing or hearing loss

• Unusual bleeding or bruising

• Severe allergic reaction

• Any new or unusual symptoms

• Worsening of pre-existing medical conditions

Understanding Erectile Dysfunction and Sildenafil Mechanism of Action

What is Erectile Dysfunction?

Erectile dysfunction (ED), commonly called impotence, is a sensitive issue that affects millions of men around the world. ED refers to the inability to achieve a strong, sustained erection sufficient for sexual intercourse. It can occur due to various factors such as age, underlying health conditions, mental stress and anxiety, and lifestyle factors. Erectile dysfunction can profoundly impact a man’s self-esteem, relationships, and overall quality of life. Fortunately, effective treatments are available for ED, one of the most common ones being an oral tablet called sildenafil citrate (Viagra), also called the “little blue pill.” Learn more about what causes erectile dysfunction.

How Does Sildenafil Work?

To understand how sildenafil works, we need to understand the physiological processes involved in achieving an erection.

Sexual stimulation causes a chemical called nitric oxide (NO) to be released in the penile tissues. This chemical relaxes the smooth muscles and blood vessels in the spongy tissue of the penis called the corpus cavernosum. As a result, there is increased blood flow into the cavernous spaces in the penis, which leads to the development of an erection.

The body releases an enzyme called phosphodiesterase type 5 (PDE5) to end the erection and reduce blood flow to the penis. 

Sildenafil works by blocking the action of an enzyme called phosphodiesterase type 5 (PDE-5) or, more specifically, cGMP-specific phosphodiesterase type- 5. Cyclic guanosine monophosphate (cGMP) is a substance that induces the relaxation of smooth muscle (which is favorable for achieving and maintaining an erection). 

In other words, sildenafil and other drugs in this class prevent the breakdown of cGMP by blocking PDE-5. Increased levels of cGMP allow smooth muscle relaxation, thus promoting blood flow to the penis to achieve and sustain an erection in response to sexual arousal.

Sildenafil effects occur also through dilation (widening) of the blood vessels in the penis, thereby increasing blood flow and causing the penis to become erect and rigid.