What is Sildenafil: how does it work, side effects, dosages, and more!
Remote Pharmacy Research Team
September 12, 2025
Sildenafil is one of the most widely used medications for treating erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). Originally developed to improve blood flow to the heart, it was later found to have a powerful effect on increasing blood flow to the penis, making it effective for ED treatment. It works by relaxing muscles and arteries in specific areas of the body, allowing for increased circulation. Today, Sildenafil is available in both brand-name and generic versions, with flexible dosage options, and is used by millions of men around the world to support sexual performance and cardiovascular health.
Sildenafil is a prescription ED medication classified as a phosphodiesterase type 5 (PDE5) inhibitor. It was first developed in the late 1980s and approved by the FDA in 1998 under the brand name Viagra. The drug quickly became one of the most recognized treatments for erectile dysfunction (ED) because of its ability to improve blood flow to the penis and support stronger, longer-lasting erections during sexual stimulation.
In addition to its role in sexual health, sildenafil is also prescribed under the brand name Revatio to treat pulmonary arterial hypertension (PAH), a condition characterized by high blood pressure in the lungs. In this context, it helps relax the blood vessels in the lungs, lowering blood pressure and improving exercise capacity.
Sildenafil works by blocking the PDE5 enzyme, which naturally breaks down a chemical messenger called cGMP. When PDE5 is inhibited, cGMP levels stay higher for longer. This allows smooth muscle relaxation, improved circulation, and better response to sexual stimulation.
Because of its effectiveness and wide availability in both brand-name and generic forms, sildenafil remains a first-line treatment option for ED and is also valued for its benefits in cardiovascular-related conditions.
Sildenafil works by targeting a natural process that regulates blood flow in certain areas of the body. It belongs to the class of drugs known as PDE5 inhibitors, which block the action of the enzyme phosphodiesterase type 5 (PDE5).
When a man is sexually stimulated, the body releases nitric oxide (NO) in the penis. This triggers the production of cyclic guanosine monophosphate (cGMP), a messenger that relaxes smooth muscle tissue in the penile arteries and allows blood to flow into the erectile tissue. Normally, the PDE5 enzyme breaks down cGMP, ending the erection process. Sildenafil prevents this breakdown, keeping cGMP levels higher for longer, which helps maintain stronger and longer-lasting erections.
Beyond erectile function, sildenafil also improves blood flow in the lungs. That is why it is prescribed under the brand name Revatio for pulmonary arterial hypertension (PAH). By relaxing blood vessels in the lungs, it reduces blood pressure in the pulmonary arteries and allows the heart to work more efficiently.
It is important to note that sildenafil does not cause erections on its own. Sexual stimulation is still required to trigger the release of nitric oxide and start the cascade of events that lead to an erection.
Sildenafil is approved by the U.S. Food and Drug Administration (FDA) for two main medical uses:
Sildenafil is most widely known for treating erectile dysfunction under the brand name Viagra. It helps men achieve and maintain an erection sufficient for sexual activity by improving blood flow to the penis. This remains its primary and most common use worldwide.
Like all medications, sildenafil can cause side effects. Most are mild and temporary, but some can be more serious and require medical attention. Understanding these effects can help you use the medication safely and know when to contact a doctor.
The most frequently reported side effects are related to the drug’s effect on blood vessels and circulation. These include:
Some patients may experience vision-related changes such as blurred vision, sensitivity to light, or a bluish tint in their vision. Mild back pain and muscle aches are also possible, especially when taking higher doses.
Although rare, certain reactions require urgent medical attention. These include:
Sildenafil should never be combined with nitrate medications (used for chest pain or heart disease) because the combination can cause a dangerous drop in blood pressure. Caution is also needed with alpha-blockers and certain antifungal or antibiotic medications, as they can alter how sildenafil is processed in the body.
Many people use the names Sildenafil and Viagra interchangeably, but there are important distinctions to understand.
Sildenafil is the active pharmaceutical ingredient. It is the chemical compound responsible for the effects on blood flow and is available in both brand-name and generic forms. When prescribed as a generic, it is simply labeled “Sildenafil” on the packaging. Viagra is the brand name version of Sildenafil, first developed and marketed by Pfizer in 1998. As the original brand, Viagra is often more expensive because of its reputation and branding, although the active ingredient is the same.
Sildenafil and Tadalafil are both PDE5 inhibitors, but they differ in several important ways that affect how patients use them. Knowing the distinctions can help you and your healthcare provider decide which option better suits your lifestyle and medical needs.
Sildenafil (Viagra) usually takes 30 to 60 minutes to begin working. Its effectiveness can be delayed if taken with a high-fat meal. Tadalafil (Cialis) typically starts working within 30 minutes, and food has little effect on its absorption.
Sildenafil works for around 4 to 6 hours. Tadalafil lasts significantly longer, up to 36 hours, which is why it is often called “the weekend pill.”
Sildenafil is usually taken on demand before sexual activity. Tadalafil can be taken either as needed or in low daily doses, which allows for more spontaneity and also helps manage benign prostatic hyperplasia (BPH) symptoms.
Both medications can cause headaches, flushing, and nasal congestion. However:
Sildenafil is more likely to cause temporary vision changes, such as a bluish tint to vision. Tadalafil is more commonly associated with back and muscle pain due to its longer half-life.
No. Sildenafil is the active ingredient in Viagra, so they work the same way and have the same strength when taken in equal doses. The difference is that Viagra is the brand-name version, while sildenafil can also be prescribed as a more affordable generic. The effectiveness depends on dosage, not on whether it is brand-name or generic.
The maximum recommended dose of sildenafil for erectile dysfunction is 100 mg once per day. It should never be exceeded. For some men, smaller doses like 25 mg or 50 mg are effective and cause fewer side effects. Taking more than 100 mg does not improve results but increases the risk of side effects such as headaches, dizziness, or changes in vision. Always follow your doctor’s prescription and never self-adjust your dose.
Sildenafil should be taken 30 to 60 minutes before sexual activity. It can remain effective for up to 4 to 6 hours. For best results, avoid taking it with a heavy or high-fat meal, since this can delay absorption and reduce effectiveness. Light meals or taking it on an empty stomach often lead to a faster onset.
After taking sildenafil, blood vessels in the penis relax and allow more blood to flow when you are sexually aroused. This makes it easier to get and keep an erection. It does not cause an erection automatically; you still need sexual stimulation. Some men may notice side effects like flushing, nasal congestion, or mild headaches, but these are usually temporary and manageable.
Erectile dysfunction is common, but it does not need to control your life. With Remote Pharmacy, you can access safe, effective treatment in a simple and discreet way. Our licensed healthcare providers evaluate your health, discuss your goals, and prescribe medications like sildenafil when appropriate.
The entire process is handled online, saving you the stress of in-person visits or long wait times. Once approved, your medication is shipped directly to your door in discreet packaging, with ongoing support available whenever you need adjustments or have questions.
If you are ready to improve your sexual health and confidence, Remote Pharmacy makes the journey safe, private, and convenient.
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