Many men prescribed sildenafil (Viagra) wonder whether the medication works automatically or if sexual arousal is still required. Understanding how this phosphodiesterase type 5 (PDE5) inhibitor functions is essential for setting realistic expectations and ensuring effective use. Sildenafil facilitates erections by enhancing blood flow to the penis, but it does not bypass the body's natural requirement for sexual stimulation. This article explains the mechanism of action, clarifies common misconceptions, and provides guidance on when to seek medical advice for erectile dysfunction.

How Sildenafil Works in the Body

Sildenafil, commonly known by the brand name Viagra, belongs to a class of medications called phosphodiesterase type 5 (PDE5) inhibitors. Understanding its mechanism of action is essential to appreciating why sexual stimulation remains necessary for the medication to work effectively.

When sexual arousal occurs, the body releases nitric oxide in the erectile tissue of the penis. This chemical messenger triggers the production of cyclic guanosine monophosphate (cGMP), which relaxes the smooth muscle cells lining the blood vessels in the penis. This relaxation allows increased blood flow into the erectile tissue, resulting in an erection. However, an enzyme called PDE5 naturally breaks down cGMP, which can limit or end the erection.

Sildenafil works by selectively inhibiting the PDE5 enzyme , thereby preventing the breakdown of cGMP. This allows cGMP levels to remain elevated for longer, facilitating improved blood flow to the penis when sexual stimulation occurs. Importantly, sildenafil does not create cGMP itself—it simply prevents its degradation. The medication typically begins working within 30 to 60 minutes of ingestion and remains effective for approximately four to six hours.

The drug is absorbed through the gastrointestinal tract, with peak plasma concentrations reached within 30-120 minutes. High-fat meals can delay absorption and reduce peak concentrations, which may delay onset and lessen the effect. Sildenafil is metabolised primarily in the liver via CYP3A4 and CYP2C9 enzymes and excreted through faeces and urine. According to the SmPC and BNF, the standard starting dose is 50mg taken approximately one hour before sexual activity, which may be adjusted to 25mg or 100mg depending on efficacy and tolerability. The maximum dose is 100mg, and sildenafil should not be taken more than once daily. Lower starting doses (25mg) are recommended for older adults, those with hepatic or renal impairment, and patients taking CYP3A4 inhibitors.

Do You Still Need Stimulation If You Take Sildenafil?

Yes, sexual stimulation is absolutely necessary for sildenafil to produce an erection. This is perhaps the most important fact to understand about how this medication works. Sildenafil does not act as an aphrodisiac, nor does it automatically trigger an erection simply by being present in the bloodstream.

The medication functions as a facilitator rather than an initiator. It creates the physiological conditions that make achieving an erection easier when sexual arousal occurs, but it cannot bypass the natural requirement for sexual stimulation. Without arousal—whether physical, psychological, or both—the cascade of events leading to nitric oxide release and cGMP production does not begin. Since sildenafil's mechanism depends entirely on the presence of cGMP to inhibit its breakdown, no erection will occur without the initial sexual stimulus.

This requirement for stimulation means that erections occur only with sexual activity or arousal, which limits unintended erections at inappropriate times. The erection occurs only in response to sexual stimulation, making the medication's effects predictable.

Clinical studies referenced in the sildenafil SmPC show that the medication significantly improves erectile function compared to placebo, but only in the context of sexual stimulation. Response rates vary by the underlying cause of erectile dysfunction, with approximately 70-80% of men experiencing improved erections overall, though rates may be lower in certain groups such as those with diabetes or following prostate surgery. Understanding this fundamental principle helps set realistic expectations and ensures appropriate use of the medication.

What Happens Without Sexual Arousal

When sildenafil is taken without subsequent sexual arousal or stimulation, no erection will occur. The medication will be absorbed and circulate in the bloodstream, inhibiting PDE5 enzymes throughout its duration of action, but this biochemical effect alone is insufficient to produce an erection.

Without sexual stimulation, the initial trigger for the erectile process—nitric oxide release—does not happen. Consequently, cGMP is not produced in the erectile tissue, leaving sildenafil with nothing to act upon. The medication can only preserve cGMP that has already been created through natural arousal pathways; it cannot generate the molecule independently.

Some men may notice mild physiological effects even without arousal, such as facial flushing, headache, nasal congestion, dyspepsia (indigestion), dizziness, or visual changes (including colour tinge or blurred vision). These are common side effects resulting from PDE5 inhibition in blood vessels elsewhere in the body. However, these effects should not be confused with the medication "working" in terms of erectile function.

It is also worth noting that psychological factors play a significant role in sexual arousal. Anxiety, stress, relationship difficulties, or depression can all impair the arousal response, even when sildenafil is present. In such cases, the medication may appear ineffective, but the underlying issue is the absence of adequate sexual stimulation due to psychological barriers.

For optimal results, take sildenafil on an empty stomach where possible, avoid heavy or high-fat meals and excessive alcohol, allow 30-60 minutes before sexual activity, and try on several occasions before judging response. Remember not to take more than one dose in 24 hours. This highlights why comprehensive assessment of erectile dysfunction should address both physical and psychological factors, as recommended in NICE Clinical Knowledge Summaries.

Common Misconceptions About Sildenafil

Several widespread misconceptions about sildenafil can lead to unrealistic expectations or inappropriate use of the medication. Addressing these myths is essential for safe and effective treatment.

Misconception 1: Sildenafil is an aphrodisiac Many people mistakenly believe that sildenafil increases sexual desire or libido. In reality, the medication has no direct effect on sexual desire. It works purely on the mechanical process of achieving an erection. Men with low libido due to hormonal imbalances, psychological factors, or other causes may not benefit from sildenafil alone, as the fundamental issue of sexual interest remains unaddressed.

Misconception 2: Sildenafil causes automatic erections As discussed, sildenafil does not cause spontaneous erections. The medication requires sexual stimulation to be effective. This misunderstanding can lead to disappointment when men expect immediate results without engaging in sexual activity.

Misconception 3: Higher doses work better for everyone Whilst sildenafil is available in doses up to 100mg, higher doses do not necessarily produce better results and may increase the risk of adverse effects. According to the BNF and SmPC, the appropriate dose varies between individuals and should be determined through consultation with a healthcare professional. The recommended starting dose is 50mg, with adjustments based on response. Do not exceed 100mg and do not take more than once daily. Lower starting doses (25mg) should be considered for older adults, those with hepatic or renal impairment, and patients taking CYP3A4 inhibitors.

Misconception 4: Sildenafil works immediately The medication typically requires 30-60 minutes to take effect, and this timeframe can be extended if taken with food. Planning sexual activity accordingly is important for optimal results.

Misconception 5: Sildenafil is only for older men Erectile dysfunction can affect men of all ages due to various physical and psychological causes. Sildenafil may be appropriate for younger men when clinically indicated, though underlying causes should always be investigated.

When to Seek Medical Advice About Erectile Dysfunction

Erectile dysfunction can be an early warning sign of underlying health conditions, making medical assessment important. You should consult your GP if:

• Erectile difficulties persist for more than a few weeks or are worsening

• Erectile dysfunction is causing significant distress or affecting your relationship

• You experience erectile problems alongside other symptoms such as chest pain, shortness of breath, or extreme fatigue

• You have cardiovascular risk factors (high blood pressure, diabetes, high cholesterol, smoking) as erectile dysfunction may indicate vascular disease

• You are taking sildenafil but it is not effective despite adequate sexual stimulation

Seek urgent medical attention if:

• You develop an erection lasting more than four hours (priapism)—this is a medical emergency requiring immediate treatment to prevent permanent damage

• You experience chest pain during sexual activity

• You have sudden vision or hearing loss after taking sildenafil

NICE Clinical Knowledge Summaries recommend that assessment of erectile dysfunction should include evaluation of cardiovascular risk factors, hormonal status, psychological wellbeing, and relationship factors. Investigations often include morning total testosterone (repeated if low), HbA1c or fasting glucose, lipid profile, and blood pressure measurement. Your GP can determine whether sildenafil is appropriate or whether alternative treatments or specialist referral to urology, endocrinology or cardiology is needed.

It is important to note that Viagra Connect 50mg is available as a pharmacy medicine after assessment by a pharmacist. Other strengths and products remain prescription-only. Always obtain sildenafil through legitimate medical channels rather than unregulated online sources. Counterfeit medications may contain incorrect doses or harmful substances.

Sildenafil is contraindicated with nitrates or nitric oxide donors (including recreational 'poppers') and riociguat due to dangerous blood pressure drops. Caution is needed with alpha-blockers, and potent CYP3A4 inhibitors (e.g., ritonavir, ketoconazole). Avoid grapefruit juice and do not combine with other PDE5 inhibitors.

If you experience side effects, report them via the MHRA Yellow Card Scheme.

Frequently Asked Questions