Many men wonder whether sildenafil, commonly known as Viagra, provides an energy boost alongside its primary use for erectile dysfunction. Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor that works by increasing blood flow to the penis during sexual stimulation. However, it is not a stimulant and does not directly increase physical or mental energy levels. Any perceived boost in energy is likely psychological, related to improved confidence or reduced performance anxiety, rather than a pharmacological effect. Understanding how sildenafil actually works—and what it does not do—is essential for safe and appropriate use.

What Is Sildenafil and How Does It Work?

Sildenafil is a medicine primarily used to treat erectile dysfunction (ED) in men and, in some cases, pulmonary arterial hypertension. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. Sildenafil works by relaxing the smooth muscle in blood vessels, which increases blood flow to specific areas of the body—most notably the penis during sexual stimulation.

The mechanism of action involves blocking the enzyme PDE5, which normally breaks down cyclic guanosine monophosphate (cGMP). By inhibiting this enzyme, sildenafil allows cGMP levels to remain elevated, promoting vasodilation and improved blood flow. This effect is localised and requires sexual arousal to be effective; sildenafil does not cause spontaneous erections or increase sexual desire.

It is important to understand that sildenafil is not a stimulant and does not provide a general energy boost. The medication does not affect the central nervous system in the way that caffeine or amphetamines might. There is no official link between sildenafil use and increased physical or mental energy levels. Any perceived increase in energy is likely psychological, related to improved confidence or reduced anxiety about sexual performance, rather than a direct pharmacological effect of the drug.

Sildenafil is available in various strengths (25mg, 50mg, and 100mg tablets). In the UK, sildenafil 50mg (Viagra Connect) can be supplied by a pharmacist after a suitability assessment, while other strengths and uses require a prescription. It is typically taken approximately one hour before sexual activity. The effects can last for up to four hours, though this varies between individuals.

Common Effects and Side Effects of Sildenafil

When taken as directed, sildenafil is generally well-tolerated, but like all medicines, it can cause side effects in some people. Understanding both the intended effects and potential adverse reactions is essential for safe use.

Common side effects reported by patients include:

• Headaches – very common, affecting more than 1 in 10 users

• Facial flushing – a sensation of warmth and redness in the face and neck

• Indigestion or dyspepsia – stomach discomfort or heartburn

• Nasal congestion – a blocked or stuffy nose

• Dizziness – particularly when standing up quickly

• Visual disturbances – temporary changes in colour vision (often a blue tinge) or increased sensitivity to light, partly due to sildenafil's minor effect on PDE6 in the retina

These effects are usually mild to moderate and tend to resolve within a few hours as the medication is metabolised. They occur because sildenafil can affect blood vessels throughout the body, not just in the genital area.

More serious but rare side effects require immediate medical attention and include:

• Sudden vision loss in one or both eyes (which may be non-arteritic anterior ischaemic optic neuropathy, NAION)

• Sudden hearing loss or ringing in the ears

• Chest pain or irregular heartbeat

• Priapism (an erection lasting more than four hours)

• Severe allergic reactions with breathing difficulties or swelling

Some men report feeling more alert or energised after taking sildenafil, but this is not a recognised pharmacological effect. Any such sensation is more likely attributable to improved mood, reduced performance anxiety, or the psychological impact of successful treatment rather than a direct stimulant action. Sildenafil does not directly increase testosterone levels, metabolic rate, or physical stamina beyond its specific vascular effects.

If you experience any side effects, talk to your doctor or pharmacist. You can also report side effects directly via the Yellow Card Scheme at yellowcard.mhra.gov.uk.

When to Speak to Your GP About Sildenafil

If you are considering sildenafil for erectile dysfunction or have concerns about your current prescription, it is important to have an open conversation with your GP. Erectile dysfunction can be an early indicator of underlying health conditions, including cardiovascular disease, diabetes, or hormonal imbalances, so proper medical assessment is essential.

You should speak to your GP if:

• You are experiencing persistent erectile dysfunction and have not yet been assessed

• You have tried sildenafil and it is not working effectively

• You are experiencing bothersome side effects that affect your quality of life

• You have any cardiovascular conditions, including angina, heart failure, or a history of heart attack or stroke

• You are taking nitrate medications (such as glyceryl trinitrate for angina) or nicorandil, as the combination can cause dangerous drops in blood pressure

• You have severe liver or kidney disease

• You have been advised to avoid sexual activity due to health reasons

Seek urgent medical attention (call 999 or go to A&E) if you experience:

• Chest pain during or after sexual activity

• An erection lasting longer than four hours (priapism)

• Sudden loss of vision or hearing

• Signs of a severe allergic reaction (difficulty breathing, swelling of face or throat)

Your GP can conduct appropriate investigations to identify any underlying causes of erectile dysfunction, which may include blood pressure measurement, cardiovascular risk assessment, blood tests to check early-morning testosterone (which may need repeating if borderline), glucose, HbA1c, lipids, and kidney and liver function. According to NICE guidance, management should address both the physical and psychological aspects of ED, and may include lifestyle modifications, treatment of underlying conditions, and psychological support where appropriate.

Your doctor may refer you to a specialist (urologist, endocrinologist, or psychosexual therapist) if there are concerns about an underlying condition, if ED is severe or not responding to treatment, or if there are other complications such as Peyronie's disease.

Safe Use of Sildenafil: NHS Guidance

To use sildenafil safely and effectively, it is essential to follow NHS and MHRA guidance, as well as your doctor's specific instructions. In the UK, sildenafil 50mg (Viagra Connect) is available from pharmacies following assessment by a pharmacist, while other strengths and uses require a prescription.

Key safety considerations include:

Dosage and timing: Take sildenafil approximately 30-60 minutes before sexual activity. The usual starting dose is 50mg, which may be adjusted by your doctor to 25mg or 100mg depending on effectiveness and tolerability. Do not take more than one dose in 24 hours. Sildenafil can be taken with or without food, though high-fat meals may delay its absorption. For adults aged 65 years or over and those with liver or kidney impairment, a lower starting dose of 25mg may be recommended.

Drug interactions: Sildenafil can interact dangerously with several medications:

• Never take sildenafil if you are using nitrates (for chest pain), nicorandil, or riociguat (for pulmonary hypertension), as this combination can cause life-threatening drops in blood pressure.

• Use with caution with alpha-blockers (used for prostate problems or high blood pressure). Only start sildenafil if you are stable on alpha-blocker therapy, consider a lower 25mg dose, and separate dosing times to minimise hypotension risk.

• Strong CYP3A4 inhibitors (such as ritonavir, ketoconazole, itraconazole, erythromycin) may increase sildenafil levels. With ritonavir, limit sildenafil to 25mg not more often than every 48 hours.

• CYP3A4 inducers (such as rifampicin) may reduce sildenafil effectiveness.

• Avoid grapefruit juice as it may increase sildenafil blood levels.

• Do not use with other PDE5 inhibitors or erectile dysfunction treatments.

Alcohol and recreational drugs: Limit alcohol consumption when taking sildenafil, as excessive drinking can reduce its effectiveness and increase the risk of side effects such as dizziness and low blood pressure. Avoid recreational drugs, particularly 'poppers' (amyl nitrite), which contain nitrates and can cause dangerous interactions.

Purchasing safely: Only obtain sildenafil through legitimate sources—your GP, NHS services, or registered UK pharmacies. The MHRA warns that counterfeit erectile dysfunction medicines purchased online may contain harmful ingredients or incorrect doses. Unregulated products pose serious health risks.

Lifestyle factors: The NHS recommends addressing modifiable risk factors for erectile dysfunction, including smoking cessation, maintaining a healthy weight, regular physical activity, and moderating alcohol intake. These lifestyle changes can improve both erectile function and overall cardiovascular health, potentially reducing the need for medication or improving its effectiveness.

Frequently Asked Questions