Viagra (Sildenafil) Effects and Side Effects | Duration, Dosage, and Precautions

Sildenafil, the active ingredient in Viagra^®, belongs to a class of drugs known as PDE5 (phosphodiesterase type 5) inhibitors. By selectively inhibiting PDE5 enzymes in the corpus cavernosum of the penis, sildenafil prevents the breakdown of cGMP (cyclic guanosine monophosphate), a vasodilating substance, thereby increasing blood flow to the penis.

Because sildenafil has a high selectivity for PDE5 in the penile corpus cavernosum, it is unlikely to significantly affect blood vessels elsewhere in the body. However, since it can cause a slight decrease in blood pressure, concurrent use with nitrates (such as nitroglycerin) is contraindicated. If you are considering sildenafil, always inform your physician of all medications you are currently taking.

The development of Viagra^® dates back to the 1980s when Pfizer began researching sildenafil as a potential new drug for angina pectoris. Although its efficacy for angina fell short of expectations, trial participants reported improvements in erectile function, prompting a shift in development toward ED treatment.

• March 1998: The U.S. FDA (Food and Drug Administration) approved sildenafil as the world’s first ED medication
• January 1999: Japan’s Ministry of Health (now MHLW) granted approval for manufacture and sale — a remarkably fast approval process taking only six months from application
• 2014: Pfizer’s patent partially expired, enabling domestic production of generic sildenafil in Japan

The rapid approval in Japan was driven by growing public health concerns over health damage caused by personal imports of unregulated products. There was an urgent need to establish a safe, legitimate prescribing environment. Today, patients can safely receive prescriptions at specialized clinics such as Men’s Care Clinic after a proper physician consultation.

Currently, Viagra^®-related products available in Japan fall into three main categories:

• Brand-name Viagra (Pfizer): Available in 25 mg and 50 mg tablets. Characterized by its iconic blue diamond-shaped pill. The marketing authorization holder Viatris discontinued supply in 2021, and only remaining stock is in circulation
• Viagra OD Film: An orally disintegrating film (25 mg and 50 mg) that dissolves in the mouth without water, offering excellent portability and rapid dissolution
• Sildenafil Tablets (Generic): Manufactured by multiple companies including Towa Pharmaceutical, Kissei Pharmaceutical, and Fuji Chemical Industries. These contain the same active ingredient and provide equivalent efficacy at a significantly lower cost

Men’s Care Clinic offers both brand-name and generic options, with prescriptions starting at 880 yen per tablet on a pay-per-visit basis. If you are unsure which type is right for you, our physicians will recommend the best option during your free initial consultation. Feel free to reach out.

The mechanism of erection can be summarized in the following steps:

• Step 1 (Sexual Stimulation): When the brain receives sexual stimuli, nitric oxide (NO) is released to the penis via nerve signals
• Step 2 (Vasodilation): NO triggers the production of cGMP, which relaxes the smooth muscle in the corpus cavernosum. Blood vessels dilate, allowing a large volume of blood to flow in
• Step 3 (Erection): The corpus cavernosum fills with blood, and the resulting pressure produces an erection
• Step 4 (Resolution): PDE5 enzymes break down cGMP, blood flow decreases, and the erection subsides

In men with ED, PDE5 enzymes work excessively at Step 4, preventing adequate cGMP levels from being maintained and making it difficult to sustain an erection. Sildenafil inhibits PDE5, thereby slowing the breakdown of cGMP and supporting the maintenance of an erection.

Viagra^® is perceived as highly effective because this inhibitory action works clearly and rapidly. Patients can feel the effects within 30 minutes to 1 hour after administration, providing a noticeable sense of improvement. If you are experiencing symptoms, we recommend consulting a physician.

A common misconception about Viagra^® is that it automatically causes an erection. This is not accurate. Sildenafil is a medication that assists the body’s response to sexual stimulation; without sexual arousal, no erection will occur.

In other words, even while taking sildenafil, an erection will not happen spontaneously during a meeting or a meal. This should be reassuring for those concerned about embarrassment or the medication being noticeable to others.

Additionally, sildenafil is effective for psychogenic ED (ED caused by stress or anxiety). Psychogenic factors are particularly common in ED among men in their 20s. A successful experience aided by medication can help rebuild confidence, and in some cases, patients find improvement even without continued medication use. This is one of the reasons many patients choose sildenafil as their first ED treatment.

Patients who have been prescribed sildenafil (Viagra^®) at our clinic have shared feedback such as the following (these are individual experiences and do not guarantee results):

• Male, 40s: “I had been struggling with ED for about six months, but I noticed improvement from the very first dose of sildenafil 50 mg. I wish I had consulted a doctor sooner.”
• Male, 30s: “Work stress was causing me to lose my erection midway through. Using sildenafil helped me build positive experiences, and after three months, I was fine without medication.”
• Male, 50s: “Age-related ED had progressed to the point where I had nearly given up, but even 25 mg provided remarkable results. The only side effect was mild flushing, which was not a problem.”

Domestic clinical trial data also confirms that approximately 74% of patients taking sildenafil 50 mg reported improvement in erectile function. Individual responses may vary, so please consult your physician about optimal dosage and administration tips.

When taken on an empty stomach, sildenafil’s plasma concentration rises within approximately 30 minutes to 1 hour, and effects become noticeable. The time to maximum plasma concentration (Tmax) is approximately 1 hour, making it ideal to take the medication 1 hour before sexual activity.

However, when taken after a meal, Tmax is delayed, and it may take more than 2 hours for effects to appear. Many people who feel that sildenafil “isn’t working” are likely experiencing reduced absorption due to food. Taking the medication on an empty stomach ensures the most reliable onset of action.

The plasma half-life of sildenafil is approximately 3 to 5 hours. This allows effective plasma concentrations to be maintained for 4 to 6 hours after administration. Effects peak at 1 to 2 hours post-dose and then gradually diminish.

• 30 min to 1 hour post-dose: Effects begin to appear
• 1 to 2 hours post-dose: Peak effect. The most stable period of efficacy
• 3 to 4 hours post-dose: Effects persist but begin to diminish slightly
• 5 to 6 hours post-dose: Effects gradually subside

The “4 to 6 hours” range is an approximation and may vary depending on individual metabolism. Elderly patients and those with reduced hepatic or renal function may experience prolonged effects. Please consult your physician about the optimal timing for your situation.

Many people search for information about sildenafil’s plasma concentration curve, so here is an accessible explanation. The sildenafil plasma concentration profile has the following characteristics:

• Rapid onset: When taken on an empty stomach, plasma concentration rises sharply within 15 to 30 minutes. Absorption is faster compared to other ED medications
• Distinct peak: Maximum plasma concentration (Cmax) is reached at approximately 1 hour (Tmax). This pronounced peak is what contributes to the perception of strong effectiveness
• Relatively rapid clearance: With a half-life of 3 to 5 hours, levels gradually decline and fall below the effective concentration around 6 hours

This rapid onset and distinct peak contribute to sildenafil’s reputation for “noticeable results.” In contrast, tadalafil (Cialis^®) features a gradual rise with sustained action over a longer period, producing a “gentle curve.” Generally, sildenafil is recommended for those who want to clearly feel the peak effect, while tadalafil (Cialis^®) is suited for those who prefer natural, extended coverage. Please consult your physician for personalized guidance.

The table below compares sildenafil (Viagra^®) 25 mg and 50 mg:

There is no significant difference in duration of action or time to onset between the two dosages; both take effect within 30 minutes to 1 hour and last 4 to 6 hours. The main differences are in “strength of effect” and “likelihood of side effects.”

For first-time sildenafil users, starting with 25 mg is recommended for the following three reasons:

• Lower side effect risk: Side effects such as headache, flushing, and nasal congestion are less likely, reducing anxiety for first-time users
• Establishes a baseline: If 25 mg provides sufficient effect, you can continue ED treatment with minimal side effects
• Room for dose escalation: If 25 mg is insufficient, you can step up to 50 mg. Starting at 50 mg, however, leaves dose reduction as the only option

However, for patients aged 65 and older or those with impaired hepatic or renal function, metabolism may be slower and plasma concentrations may remain elevated, so 25 mg may be set as the maximum dose. Never increase your dose on your own — always follow your physician’s instructions.

If you feel that sildenafil is not working effectively, there are several possible explanations:

• Taking it after a meal: Sildenafil is highly susceptible to the effects of food, especially high-fat meals, which significantly reduce absorption. Taking it on an empty stomach is most effective
• Insufficient sexual stimulation: Sildenafil requires sexual arousal to work; taking the medication alone will not produce an erection
• Insufficient dosage: If 25 mg is not effective, consult your physician about increasing to 50 mg
• Strong psychological tension: Anxiety about whether the medication will work, especially on the first attempt, can paradoxically worsen ED. Try 2 to 3 times before making a judgment
• Underlying medical conditions: Conditions such as diabetes, hypertension, or dyslipidemia that affect the vascular system may reduce the efficacy of ED medications

Even if sildenafil proves insufficient, switching to tadalafil (Cialis^®) or vardenafil (Levitra^®) may lead to improvement. Do not give up after one medication fails — speak openly with your physician.

Among the three ED medications available, sildenafil (Viagra^®) is the most susceptible to the effects of food. In particular, consuming high-fat meals (such as barbecue, ramen, or fast food) before taking the medication can significantly reduce intestinal absorption, delaying onset or weakening the effect.

• Ideal timing: 1 hour before a meal, or at least 2 hours after eating. Take approximately 1 hour before sexual activity
• Light meals have minimal impact: A small amount of food like a rice ball or salad is generally fine (but avoid fatty foods)
• If taken after eating: It may take more than 2 hours for effects to appear. Be patient and do not rush

For situations like a dinner date before going to a hotel, consider taking sildenafil before the meal, or keeping the meal low in fat. If you are unsure about timing, consult your physician.

“Can I take Viagra with alcohol?” is a very common question. The answer is that a small amount of alcohol is generally acceptable, but heavy drinking should be avoided.

A modest amount of alcohol (1 to 2 beers or 1 to 2 glasses of wine) may actually help with psychogenic ED through its relaxation effects. However, both sildenafil and alcohol have vasodilatory and blood pressure-lowering effects, so combining them with large amounts of alcohol increases the risk of excessive blood pressure drop, dizziness, and lightheadedness.

• Small amount (1–2 beers): Minimal impact. May even have a positive relaxation effect
• Moderate amount (3–4 beers): Effect may be diminished; side effects (headache, flushing) are more likely
• Large amount (intoxication level): Effect is largely lost. Risk of dizziness and hypotension

If you frequently find yourself in social drinking situations, consider keeping your alcohol intake moderate, or switching to tadalafil (Cialis^®), which is less affected by alcohol. Please consult your physician first.

There are currently three ED medications approved in Japan: sildenafil (Viagra^®), tadalafil (Cialis^®), and vardenafil (Levitra^®). Each has unique characteristics, and the best choice depends on your lifestyle and the severity of your ED.

Sildenafil (Viagra^®) is suited for: First-time ED medication users, those who want to clearly feel peak effects, and those who prefer the medication to clear the body quickly

Tadalafil (Cialis^®) is suited for: Those who do not want to worry about timing, those who want extended weekend coverage, and those who want to eat freely

Vardenafil (Levitra^®) is suited for: Those who prioritize rapid onset, and those who want flexibility around mealtimes

Men’s Care Clinic carries all three medications, so you can choose the best option with your physician during your initial consultation. For more information, please also see our ED treatment page.

The following are the most common side effects of sildenafil (Viagra^®). All are related to its vasodilatory action and typically resolve on their own within 4 to 6 hours as the medication wears off.

• Headache (approx. 10–15%): The most common side effect. A temporary headache caused by vasodilation that can be managed with over-the-counter pain relievers (such as ibuprofen). Many patients find this side effect diminishes with repeated use
• Facial flushing (approx. 10%): Redness or warmth in the face. A vasodilatory response similar to what occurs when drinking alcohol, with no health concerns
• Nasal congestion (approx. 5%): Caused by dilation of blood vessels in the nasal mucosa. Unlike congestion from a cold, it resolves as the medication wears off
• Indigestion/stomach discomfort (approx. 3%): Related to effects on gastric acid secretion. Often mitigated by taking the medication on an empty stomach
• Visual changes (approx. 2%): Temporary visual disturbances such as a blue tinge or increased light sensitivity. These typically resolve within a few hours

Side effect intensity tends to correlate with dosage. If side effects are a concern, we recommend starting with 25 mg to gauge your response. Please do not hesitate to inform your physician of any symptoms you experience.

Many people search for information about whether Viagra^® causes hair loss or thinning. The definitive answer is: there is no scientific evidence that sildenafil, the active ingredient in Viagra, causes androgenetic alopecia (AGA).

The primary cause of AGA is the conversion of testosterone to DHT (dihydrotestosterone) by the enzyme 5-alpha reductase, which then acts on androgen receptors in hair follicle cells to shorten the hair growth cycle. Sildenafil’s mechanism of action involves PDE5 inhibition and vasodilation, and it has no direct effect on the hormonal system.

In fact, recent research has suggested that the improved scalp blood flow from PDE5 inhibitors may potentially promote hair growth. A study published in the Journal of Dermatological Treatment in 2019 reported that topical sildenafil may promote hair growth. The claim that “Viagra causes hair loss” is a misconception with no medical basis; current evidence actually suggests the opposite effect may be possible.

If you have noticed thinning hair since starting sildenafil, it is most likely that AGA is progressing independently of the medication. AGA can begin in the late 20s for many men, and its onset may simply coincide with the start of ED treatment. If hair loss is a concern, we recommend seeking a separate AGA-specific consultation.

While sildenafil (Viagra^®) has an established safety profile, the following individuals must not take this medication (contraindicated):

• Patients currently taking nitrates: Including nitroglycerin and isosorbide dinitrate. Concurrent use can cause a dangerous, life-threatening drop in blood pressure. This is the most critical contraindication
• Patients with severe cardiovascular disease: Including unstable angina, or those who have had a myocardial infarction or stroke within the past 6 months
• Patients with severe hepatic impairment: Drug metabolism may be significantly delayed, leading to unpredictable increases in plasma concentration
• Patients with hypotension (systolic BP below 90 mmHg): Risk of excessive blood pressure reduction
• Patients with retinitis pigmentosa: This retinal condition involves PDE6, and sildenafil has mild activity on PDE6, requiring caution

Additionally, the following serious adverse reactions have been reported in rare cases:

• Priapism: If an erection persists for more than 4 hours, there is a risk of penile tissue necrosis, and immediate emergency medical care is required
• Sudden sensorineural hearing loss: Extremely rare, but sudden hearing reduction has been reported. Seek immediate medical attention if you experience auditory abnormalities after taking the medication
• Non-arteritic anterior ischemic optic neuropathy (NAION): Extremely rare. Seek immediate medical attention if you experience sudden vision loss or visual field defects

While these serious side effects are extremely rare, it is important to be aware of them. At Men’s Care Clinic, we carefully review medical history and current medications during the initial consultation to ensure safe prescribing. If you have any concerns about whether sildenafil is safe for you, that is all the more reason to consult a physician first.

All generic sildenafil products approved in Japan have passed bioequivalence testing conducted under the oversight of the Ministry of Health, Labour and Welfare. This testing scientifically confirms that the generic produces “plasma concentration profiles equivalent to the brand-name drug, meaning equivalent efficacy.”

• Towa Pharmaceutical “Sildenafil OD Tablets VI ‘TOWA'”: Orally disintegrating tablet format. Can be taken without water
• Kissei Pharmaceutical “Sildenafil Tablets VI ‘KISSEI'”: Standard tablet format. Known for consistent quality and highly trusted by medical institutions
• Fuji Chemical Industries “Sildenafil Tablets VI ‘FCI'”: Available in multiple strengths. Excellent cost-performance ratio

Some people hold the misconception that “generics don’t work,” but this has no medical basis. The sildenafil content is identical to the brand-name product, and there is no difference in efficacy. However, due to differences in inactive ingredients, a small number of patients may notice a “slightly different dissolution rate.” If this is a concern, please consult your physician.

Men’s Care Clinic prescribes both brand-name Viagra^® and domestically approved generic sildenafil starting at 880 yen per tablet. Since ED treatment is not covered by national health insurance (it is a self-pay treatment), the full cost is borne by the patient; however, we strive to keep our pricing as affordable as possible.

• Initial consultation and counseling fee: Free
• Prescription fee: Included in the medication price (no separate charge)
• Pay-per-visit: No subscription plans or bulk-purchase requirements. Prescriptions available from as little as one tablet
• Payment methods: Cash and all major credit cards accepted

While many people assume ED treatment is expensive, generic sildenafil starts at just 880 yen per dose. We never pressure patients into subscription plans. You are welcome to start with just one tablet. If cost is a concern, please feel free to discuss it with us.

Here is why so many patients choose Men’s Care Clinic for ED treatment:

• Transparent pricing from 880 yen per tablet: Sildenafil (Viagra^®) prescribed from 880 yen per tablet with no hidden fees
• Pay-per-visit, one tablet at a time: No subscription plans or bulk-purchase pressure. Purchase only what you need
• Free initial consultation and counseling: You pay only for the medication, keeping the barrier to your first visit low
• Fully appointment-based: No long waits in the waiting room. Minimal chance of encountering other patients
• 3 convenient locations: Consistent, high-quality treatment at Shimbashi, Akihabara, and Omotesando
• All 3 ED medications available: Brand-name and generic sildenafil (Viagra^®), tadalafil (Cialis^®), and vardenafil (Levitra^®). Our physicians recommend the best match for your symptoms and lifestyle
• Toyosu Hospital (Showa University affiliated) partnership: Comprehensive medical backup system in place

While many perceive ED treatment as expensive or intimidating, our clinic operates on the philosophy of “accessible, safe, and fairly priced” care. For more details, please visit our ED treatment page.

For patients who cannot visit our clinics in person or prefer not to consult face-to-face, Men’s Care Clinic also offers online consultations.

• Consult from home: Receive a physician consultation via video call on your smartphone or computer
• Medication delivered to your door: Prescribed medications are shipped in discreet packaging with no indication of the contents
• Available nationwide: Patients who cannot travel to Shimbashi, Akihabara, or Omotesando can still receive treatment
• First-time offer: Online consultation exclusive — first-time tadalafil (Cialis^®) generic 10 tablets for 5,000 yen (less than half the regular price)

Counseling is free for online consultations as well. The same medical interview process applies: we confirm your medical history, current medications, and ED symptoms to ensure safe prescribing. Even if you just want to learn more before committing, you are welcome to book an appointment. Feel free to schedule a consultation.

In both domestic and international clinical trials, approximately 70 to 80% of patients taking sildenafil (Viagra^®) 50 mg reported improvement in erectile function. As the world’s first ED medication with over 25 years of prescribing history, its efficacy and safety have been the most extensively validated. Individual responses may vary, so please consult a physician for personalized advice.

The duration of action of sildenafil (Viagra^®) is approximately 4 to 6 hours. Effects peak at 1 to 2 hours post-dose and then gradually diminish. With a half-life of 3 to 5 hours, the effect is largely gone after 6 hours. If you prefer longer-lasting coverage, tadalafil (Cialis^®), which lasts 24 to 36 hours, is also an option.

When taken on an empty stomach, effects typically begin within 30 minutes to 1 hour. Taking it 1 hour before sexual activity provides the best results. If taken after a meal, onset may be delayed by more than 2 hours, so we recommend taking it on an empty stomach. Please consult your physician if you need guidance on timing.

There is no scientific evidence that sildenafil, the active ingredient in Viagra, causes androgenetic alopecia (AGA). AGA is caused by DHT (a male hormone derivative), while sildenafil is a PDE5 inhibitor that does not directly affect the hormonal system. In fact, research has explored the possibility that improved scalp blood flow from PDE5 inhibition may promote hair growth. If hair loss is a concern, we recommend seeking a separate AGA-specific consultation.

For first-time users, starting with 25 mg is recommended. This minimizes side effect risk and allows for dose escalation to 50 mg if needed. The 50 mg dose is typically prescribed for moderate to severe ED. The appropriate dosage varies based on age, weight, and underlying conditions, so please consult your physician.

Approximately 20 to 30% of patients do not experience adequate results. Common reasons include taking it after a meal, insufficient sexual stimulation, inadequate dosage, or strong psychological tension. We recommend reviewing your administration method and trying 2 to 3 times before making a judgment. If sildenafil remains ineffective, switching to tadalafil (Cialis^®) or vardenafil (Levitra^®) often yields better results.

Yes, the active ingredient, efficacy, and safety are identical to the brand-name product. Generic medications are approved by the Ministry of Health, Labour and Welfare only after passing bioequivalence testing that confirms they match the brand-name product. The only differences are in tablet appearance, inactive ingredients, and price. Our clinic prescribes generics starting at 880 yen per tablet.

Taking sildenafil after a meal can significantly reduce its effectiveness. This is especially true after high-fat meals, which markedly decrease absorption. Ideally, take it before a meal or at least 2 hours after eating. A light snack (such as a rice ball or salad) has minimal impact, but for maximum efficacy, taking it on an empty stomach is best.

A small amount of alcohol (1 to 2 beers) is generally fine. However, heavy drinking can diminish sildenafil’s effects and increase the risk of dizziness and hypotension. Both sildenafil and alcohol have vasodilatory effects, so excessive combination should be avoided. If you frequently drink heavily in social settings, please discuss this with your physician.

Common side effects such as headache, flushing, and nasal congestion typically resolve on their own within 4 to 6 hours as the medication wears off. It is rare for side effects to persist into the next day. If symptoms continue beyond the following day, please consult your physician, as a dosage adjustment or medication change may be needed.

Sildenafil (Viagra^®) should be taken no more than once within a 24-hour period, limited to one tablet per day. Daily use is not recommended. The standard approach is to use it as needed (on an as-needed basis) timed to sexual activity. If daily use is preferred, tadalafil (Cialis^®) 2.5 mg or 5 mg, which is designed for daily administration, is an alternative worth discussing with your physician.

Sildenafil (Viagra^®) is a prescription medication and cannot be purchased without a physician’s prescription in Japan. Personal import services and online purchases occupy a legal gray area and carry an extremely high risk of counterfeit products (those lacking the active ingredient or containing impurities). According to WHO (World Health Organization) surveys, approximately 50% of ED medications sold on the internet are counterfeit. For your safety, always obtain a legitimate prescription from a medical institution. Our clinic also offers online consultations for your convenience.