Sildenafil Side Effects: What's Common, What's Not, When to Seek Help

Side effects are the part of a medicine conversation people most want straight information about, and the part most likely to be either glossed over by sellers or catastrophised online. This article sets out the recognised side-effect categories for sildenafil, explains why several of them occur, and identifies the warning signs that warrant urgent care.

It is general education. The authoritative source for any specific product is the consumer medicine information supplied with a lawfully dispensed medicine, and your prescriber or pharmacist.

First, the context

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor and a Schedule 4 prescription-only medicine in Australia. A prescription from a registered Australian prescriber is required. Part of what that prescriber is doing is weighing likely side effects against your circumstances — which is exactly why the assessment exists.

The TGA prohibits advertising prescription-only medicines directly to consumers, so this article describes rather than recommends.

Why several side effects happen at all

Understanding the mechanism makes the side-effect list far less mysterious.

PDE5 inhibitors act on an enzyme involved in relaxing the smooth muscle in blood vessel walls. That enzyme is not confined to one part of the body. When blood vessels relax more widely, the results are predictable: increased blood flow to the face and nasal passages, a change in blood pressure, and effects on the vessels supplying the head.

That is why headache, facial flushing and a blocked or runny nose top the recognised list. They are the same action showing up elsewhere, not a sign of something going wrong.

Commonly recognised effects

Effects widely recognised for sildenafil include:

• Headache, the most frequently reported.
• Facial flushing — warmth or redness in the face and neck.
• Nasal congestion or a runny nose.
• Indigestion or reflux.
• Dizziness, related to blood pressure changes.
• Back or muscle discomfort.
• Visual disturbance — a temporary blue tinge to vision, increased light sensitivity or slightly blurred vision. This reflects a small amount of activity at a related enzyme in the retina and is typically transient.

Most of these are described as mild and self-limiting. That does not make them inevitable, and it does not mean they should be dismissed if they are troubling you — a prescriber may be able to change something.

Less common effects worth knowing about

Less frequently reported effects include palpitations, nosebleeds, dry mouth or dry eyes, ringing in the ears, and rash. Fainting can occur, particularly where blood pressure falls more than expected, and this is more likely alongside alcohol, dehydration, or other blood-pressure-lowering medicines.

The red flags: stop and seek urgent care

These are uncommon, but they are the reason this class is prescription-controlled and monitored.

• Chest pain, pressure or tightness during or after sexual activity. Call emergency services. Tell the treating team you have taken a PDE5 inhibitor and when, because nitrate-based emergency treatments cannot safely be given.
• An erection lasting more than four hours (priapism), especially if painful. This is a medical emergency. Delay can lead to permanent tissue damage, so do not wait to see if it resolves.
• Sudden loss or reduction of vision in one or both eyes. This has been associated with a rare condition affecting the optic nerve. Stop and seek immediate assessment.
• Sudden hearing loss or ringing in the ears, with or without dizziness. Also requires immediate assessment.
• Signs of an allergic reaction — swelling of the face, lips or throat, difficulty breathing, widespread rash.
• Fainting or collapse.

What raises the likelihood of trouble

Side-effect risk is not fixed. It rises with:

• Interacting medicines. Certain antifungals, macrolide antibiotics and HIV protease inhibitors slow the clearance of sildenafil and raise circulating levels; grapefruit juice is commonly cited.
• Other blood-pressure-lowering medicines, including alpha-blockers, which need careful medical management.
• Alcohol, which lowers blood pressure in its own right and compounds dizziness.
• Dehydration, heat, and standing up quickly.
• Kidney or liver impairment, which affect how the body handles the medicine.
• Taking a product not prescribed to you, or one whose contents have never been verified.

The absolute contraindication

Nitrates must never be combined with a PDE5 inhibitor. That includes glyceryl trinitrate sprays, patches and tablets, isosorbide products, and the recreational inhalants known as poppers. The combination can produce a sudden, severe and potentially fatal fall in blood pressure. Riociguat is also contraindicated. This applies regardless of brand, strength or format, and there is no version of it that a website can advise you around.

Significant cardiovascular disease — recent heart attack or stroke, unstable angina, uncontrolled hypertension, severe heart failure, some arrhythmias — needs to be assessed before any PDE5 inhibitor is considered, because sexual activity itself places demand on the heart.

Counterfeits change the side-effect picture entirely

If a product has not been through regulatory assessment, its side-effect profile is unknown, because its contents are unknown. The TGA has warned repeatedly that products in this category sold through unregulated overseas channels have been found to contain undeclared pharmaceutical ingredients, the wrong amounts, or contaminants.

An unexpected or severe reaction to a product of unverified origin should be treated as a medical issue first and a purchasing lesson second. Tell the clinician exactly what you took and bring the packaging if you can.

What to do about side effects that are not emergencies

Do not simply stop, adjust or double up on your own. Tell your prescriber or pharmacist what you experienced, when it started, how long it lasted and how troubling it was. There are often options — a different ingredient in the class, a different approach, or addressing an interacting medicine. Adverse events can also be reported to the TGA, which is how safety signals are picked up over time.

the Australian Commission on Safety and Quality in Health Care publishes independent plain-English material on medicine side effects, and Healthdirect Australia is a good general starting point.

This article is general educational information about medicine side effects, not medical advice. If you experience chest pain, an erection lasting more than four hours, or sudden vision or hearing loss, seek urgent medical care. For anything else, speak with your doctor or pharmacist.