Sildenafil, widely recognised under the brand name Viagra, is a prescription medication licensed in the UK for treating erectile dysfunction and pulmonary arterial hypertension. Some gym-goers and athletes have questioned whether sildenafil might enhance workout performance by improving blood flow to muscles. However, sildenafil is not approved for exercise enhancement, and evidence supporting such use is extremely limited. Using this medication outside its licensed indications carries significant safety risks, including cardiovascular effects, drug interactions, and side effects that may be dangerous during physical activity. This article examines what sildenafil does, the risks of using it for workouts, and evidence-based alternatives for improving athletic performance safely.

What Is Sildenafil and How Does It Work?

Sildenafil is a medication licensed in the UK for treating erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. The Medicines and Healthcare products Regulatory Agency (MHRA) has approved sildenafil under brand names such as Viagra for ED and Revatio for PAH, though the active ingredient remains the same.

The drug works by inhibiting the PDE5 enzyme, which normally breaks down cyclic guanosine monophosphate (cGMP) in smooth muscle cells. When PDE5 is blocked, cGMP levels increase, leading to relaxation of smooth muscle and dilation of blood vessels. In men with erectile dysfunction, this mechanism enhances blood flow to the penis during sexual stimulation. In pulmonary hypertension, it reduces pressure in the pulmonary arteries by dilating these vessels, thereby improving exercise capacity in affected patients.

Some athletes and fitness enthusiasts have speculated that sildenafil might enhance workout performance by improving blood flow to muscles. However, evidence for this is limited and mainly restricted to high-altitude or hypoxic conditions. Sildenafil is not licensed for exercise enhancement, and its use outside approved indications carries potential risks. It is not prohibited by UK Anti-Doping (UKAD) or the World Anti-Doping Agency (WADA).

Sildenafil typically begins working within 30–60 minutes of oral administration, with effects lasting approximately four to six hours. For ED, the usual starting dose is 50 mg taken as needed (maximum once daily), though this may be adjusted between 25–100 mg based on response. High-fat meals may delay its absorption. The medication requires sexual stimulation to work for erectile dysfunction and does not cause automatic erections.

In the UK, sildenafil 50 mg (Viagra Connect) is available as a pharmacy medicine after assessment by a pharmacist. Other strengths and formulations remain prescription-only. Using sildenafil without appropriate medical guidance or for unapproved purposes is not recommended.

Potential Risks of Using Sildenafil for Workouts

Using sildenafil for exercise enhancement in healthy individuals carries several important safety concerns that must be carefully considered. The medication can cause significant adverse effects, particularly when used inappropriately or without medical supervision.

Common side effects of sildenafil include:

• Headaches – very common

• Facial flushing – due to peripheral vasodilation

• Indigestion and gastrointestinal discomfort

• Nasal congestion

• Visual disturbances – including blue-tinted vision or increased light sensitivity

• Dizziness – which could be particularly dangerous during physical activity

More seriously, sildenafil can cause cardiovascular effects that may be hazardous during intense exercise. The medication lowers blood pressure through its vasodilatory action, and when combined with the cardiovascular demands of strenuous physical activity, this could lead to symptomatic hypotension (dangerously low blood pressure), fainting, or falls. Individuals with underlying heart conditions face elevated risks of serious cardiac events.

Drug interactions present another significant concern. Sildenafil is absolutely contraindicated with:

• Nitrate medications (such as glyceryl trinitrate used for angina)

• Recreational nitrites ('poppers')

• Riociguat (used for pulmonary hypertension)

These combinations can cause life-threatening drops in blood pressure. Sildenafil also interacts with alpha-blockers (patients should be stable on alpha-blocker therapy before starting sildenafil, usually at a lower dose), potent CYP3A4 inhibitors (such as ketoconazole, itraconazole, ritonavir, and clarithromycin), and grapefruit juice, which can increase sildenafil levels in the blood.

Seek immediate medical attention if you experience chest pain, an erection lasting more than 4 hours (priapism), sudden vision or hearing loss, or severe dizziness/fainting while taking sildenafil.

The lack of evidence supporting sildenafil's efficacy for athletic performance at normal altitude means users expose themselves to these risks without proven benefit. Furthermore, obtaining sildenafil without proper medical assessment bypasses important screening for contraindications and underlying health conditions that might make its use dangerous.

If you experience any suspected side effects from sildenafil, report them through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Safe and Evidence-Based Ways to Enhance Athletic Performance

Rather than turning to prescription medications intended for other purposes, individuals seeking to improve their workout performance should focus on evidence-based strategies that are both safe and effective.

Structured training programmes form the foundation of performance enhancement. Progressive overload – gradually increasing the intensity, duration, or frequency of exercise – allows the body to adapt and improve over time. The UK Chief Medical Officers recommend at least 150 minutes of moderate-intensity aerobic activity or 75 minutes of vigorous-intensity activity weekly for adults, alongside muscle-strengthening activities on two or more days per week.

Nutrition and hydration play crucial roles in athletic performance:

• Adequate protein intake (1.2–2.0g per kilogram of body weight for active individuals, according to the British Dietetic Association) supports muscle repair and growth

• Complex carbohydrates provide sustained energy for endurance activities

• Proper hydration before, during, and after exercise maintains performance and prevents heat-related illness

• Balanced micronutrient intake through a varied diet supports overall health and recovery

Sleep and recovery are often underestimated but essential components of performance improvement. Adults should aim for seven to nine hours of quality sleep nightly, as this is when the body repairs tissues and consolidates training adaptations.

Legal sports supplements with evidence supporting their use include:

• Caffeine – shown to enhance endurance and reduce perceived exertion

• Creatine monohydrate – improves high-intensity, short-duration performance

• Beta-alanine – may benefit repeated high-intensity efforts

Before using any supplement, consider the risk of contamination with prohibited substances. UK Anti-Doping (UKAD) recommends choosing products that have been batch-tested through programmes like Informed-Sport. The NHS advises that most people can meet their nutritional needs through diet alone, and supplements should not replace a balanced eating pattern.

If you have specific performance goals, consider working with qualified professionals such as CIMSPA-registered exercise professionals or HCPC-registered dietitians and SENr-registered sports nutritionists who can provide personalised, evidence-based guidance.

When to Speak with Your GP About Exercise and Medications

Consulting your GP is essential in several circumstances related to exercise and medication use. Open communication with healthcare professionals ensures your safety and helps optimise both your health management and fitness goals.

You should contact your GP if:

• You are considering using any prescription medication for purposes other than its licensed indication

• You experience erectile dysfunction and are considering sildenafil – proper assessment can identify underlying cardiovascular or metabolic conditions requiring treatment, as ED can be an early indicator of cardiovascular disease or diabetes

• You have cardiovascular symptoms during exercise, such as chest pain, excessive breathlessness, palpitations, or dizziness

• You are taking medications and want to start a new exercise programme, particularly if you have chronic conditions like diabetes, hypertension, or heart disease

• You experience persistent fatigue or declining performance despite adequate training and recovery

Call 999 immediately if you experience chest pain, severe breathlessness, fainting, or sudden vision loss during exercise or after taking any medication. For urgent but non-emergency concerns, contact NHS 111 for advice.

Your GP can perform appropriate investigations to rule out underlying medical conditions that might affect exercise capacity. These may include blood tests to check for anaemia, thyroid dysfunction, or vitamin deficiencies, as well as cardiovascular assessments if indicated.

If you have been using sildenafil or other medications inappropriately, do not feel embarrassed to discuss this with your doctor. Healthcare professionals are there to help, not judge, and honest disclosure allows them to assess for any adverse effects and provide appropriate guidance. The NHS emphasises patient safety above all else.

For those with legitimate erectile dysfunction, your GP can assess whether sildenafil is appropriate and safe for you, considering your medical history, current medications, and cardiovascular risk factors. They can also investigate underlying causes and discuss lifestyle modifications that may help. Alternatively, pharmacists can supply Viagra Connect (sildenafil 50 mg) after a consultation to determine if it's suitable for you.

Remember that pharmacists are also accessible healthcare professionals who can provide advice about medications, potential interactions, and when GP consultation is necessary. If you have concerns about exercise, performance, or medication use, seeking professional medical advice is always the safest approach and may identify health issues requiring attention.

Frequently Asked Questions