Sildenafil is a prescription medicine used to treat erectile dysfunction (ED), the persistent difficulty in getting or keeping an erection firm enough for sexual activity. It is widely known by the original brand name Viagra, but generic sildenafil contains the same active medicine.
Sildenafil can improve erections when sexual stimulation occurs. It does not automatically produce an erection, increase sexual desire, or cure the underlying cause of ED. Persistent ED deserves a medical assessment because it may be associated with diabetes, high blood pressure, high cholesterol, obesity, smoking, medication effects, hormone problems, psychological stress, or cardiovascular disease.
How Does Sildenafil Work?
Sildenafil belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors. During sexual stimulation, nitric oxide is released in the penis. Sildenafil supports this natural pathway, helping the penile blood vessels relax and allowing more blood to enter.
How and When Is Sildenafil Taken?
Sildenafil for ED is available in 25 mg, 50 mg, and 100 mg doses. A common starting dose is 50 mg, but the prescriber may choose a lower or higher dose based on age, response, side effects, medical conditions, and other medicines.
- It is generally taken around one hour before expected sexual activity. Some men notice an effect within 30–60 minutes.
- Its useful effect usually lasts for several hours, although response and timing vary between individuals.
- Do not take more than one prescribed dose in 24 hours.
- Sexual stimulation is still required for the medicine to work.
Sildenafil can be taken with or without food, but a large or high-fat meal may delay its absorption and make it take longer to work. Heavy alcohol intake can worsen erections and increase dizziness or low blood pressure.
What If Sildenafil Does Not Work the First Time?
A first attempt may fail because the timing was wrong, the meal was too heavy, there was insufficient sexual stimulation, anxiety interfered, or the dose was unsuitable. Do not increase the dose yourself or combine sildenafil with another ED medicine. A clinician can review how it was used, check for underlying causes, and decide whether the dose or treatment should change.
Common Side Effects
Most side effects are mild and short-lived. They can include:
- Headache
- Facial flushing or a feeling of warmth
- Indigestion or nausea
- Blocked or stuffy nose
- Dizziness
- Temporary visual symptoms, such as blurred vision, light sensitivity, or a blue colour tinge
Avoid driving or operating machinery if dizziness or visual disturbance occurs. Contact the prescribing clinician if side effects are persistent or troublesome.
Who Should Not Take Sildenafil?
Never take sildenafil with nitrate medicines used for chest pain, such as nitroglycerin or isosorbide, or with recreational “poppers”. The combination can cause a dangerous fall in blood pressure. Sildenafil must also not be combined with riociguat, a medicine used for certain forms of pulmonary hypertension.
Tell the prescriber if you have unstable heart disease, a recent heart attack or stroke, low or uncontrolled blood pressure, severe kidney or liver disease, previous sudden vision loss, bleeding problems, penile curvature, sickle cell disease, leukaemia, or multiple myeloma. ED medicines are not appropriate when sexual activity itself is medically inadvisable.
Alpha-blockers and blood-pressure medicines can add to sildenafil’s blood-pressure-lowering effect. Some antibiotics, antifungals, HIV medicines, seizure medicines, and other drugs can alter sildenafil levels. Always provide the clinician with a complete list of medicines, supplements, and recreational substances.
When Is Urgent Medical Care Needed?
Seek urgent medical help for chest pain, fainting, severe breathlessness, an erection lasting longer than four hours, sudden loss or marked reduction of vision or hearing, or signs of a severe allergic reaction. If chest pain occurs after sildenafil, do not take a nitrate; tell the emergency team what you took and when.
Sildenafil and Male Fertility
Sildenafil may help couples when ED makes timed intercourse difficult, but it does not treat a low sperm count or poor sperm quality. Men who are trying to conceive and have persistent ED should be assessed for both sexual health and fertility factors.
Sildenafil or Tadalafil?
Both medicines are PDE5 inhibitors and are effective for many men. Sildenafil is generally used when needed and has a shorter window of action. Tadalafil has a longer window and also has a daily option. The best choice depends on medical history, other medicines, side effects, cost, frequency of sexual activity, and personal preference.
The Bottom Line
Sildenafil is an effective first-line treatment for many men with ED when prescribed after an appropriate health assessment. Correct timing, adequate sexual stimulation, and attention to food and alcohol can improve results. Nitrate interactions must always be ruled out.
This article provides general information and is not a prescription. Consult a qualified clinician for diagnosis and treatment suited to your health and current medicines.