Who Should Not Take Viagra? Contraindications, Drug Interactions, and Alternatives

In ED medication prescribing, “contraindication” and “cautious administration” are clearly distinguished.

• Contraindication: A condition where the medication must absolutely not be taken. Due to life-threatening risks, it will never be prescribed under any circumstances.
• Cautious administration: A condition where use is possible under certain conditions. A physician may prescribe it with dose adjustments and monitoring.

If you fall under “cautious administration,” you may still be able to take sildenafil. If a physician determines it is safe after a comprehensive evaluation, a prescription may be possible. If unsure which category applies, consult an ED specialist clinic.

Use the following checklist to assess whether sildenafil may be safe for you. If you answer “yes” to even one item, please consult a physician.

This checklist is for reference only. Final determination is always made by a physician. Feel free to consult via online consultation.

The vasodilatory effect of sildenafil produces the following systemic effects:

• Blood pressure reduction: Systemic vasodilation causes blood pressure to drop by approximately 5–10 mmHg on average
• Headache and flushing: Common side effects of sildenafil caused by vasodilation in the head and face
• Changes in cardiac load: Reduced vascular resistance alters the heart’s workload balance

For healthy individuals, these effects are minor. However, for patients with cardiovascular disease, they can be potentially fatal. The combination with nitrates is particularly dangerous as it causes a precipitous drop in blood pressure.

There are multiple PDE (phosphodiesterase) subtypes (PDE1 through PDE11). Sildenafil primarily inhibits PDE5 but also has weaker inhibitory effects on PDE6 and PDE11.

The reason retinitis pigmentosa is contraindicated is that PDE6 inhibition may further worsen visual function. Additionally, since PDE5 is also present in pulmonary vessels, interactions with pulmonary vascular medications require caution.

The following symptoms may occur when sildenafil and nitrates are used concurrently:

• Severe hypotension (systolic blood pressure dropping below 80 mmHg)
• Dizziness and lightheadedness (worsening of orthostatic hypotension)
• Syncope and loss of consciousness
• Rapid heart rate changes (reflex tachycardia or bradycardia)
• Myocardial ischemia and cardiac arrest (worst case scenario)

These symptoms can occur regardless of dosage. Never assume that “a small amount will be safe.”

All of the following medications are absolutely contraindicated with sildenafil. This includes not only prescription medications but also emergency-use sprays.

Recreational amyl nitrite (“poppers”) are also NO donors and are absolutely contraindicated. If you are taking angina medications, please inform your doctor via online consultation.

Patients who have had a myocardial infarction within the past 6 months are contraindicated. During the recovery period, the heart is vulnerable and blood pressure fluctuations may trigger re-infarction.

Patients more than 6 months post-MI with a clear exercise stress test may be prescribed at the physician’s discretion. Patients using nitrates for angina are contraindicated regardless.

• Stable angina (not using nitrates): May be prescribed at physician’s discretion
• Unstable angina: Contraindicated
• Within 6 months of MI: Contraindicated

Patients who have had a stroke or cerebral hemorrhage within the past 6 months are also contraindicated. After cerebrovascular events, blood vessels are more fragile and sudden blood pressure changes may trigger recurrence.

For patients more than 6 months post-event, prescribing may be considered if:

• Neurological sequelae are stable
• Blood pressure is adequately controlled
• Interactions with anticoagulant medications have been confirmed

Sildenafil is contraindicated when blood pressure is either too low or too high.

If taking antihypertensives, some combinations require caution. Always inform your physician of all current medications. See: detailed sildenafil information.

Sildenafil is metabolized by hepatic enzymes CYP3A4 and CYP2C9. Severe hepatic impairment (Child-Pugh Class C) is a contraindication.

In hepatic impairment, the drug’s half-life is prolonged, meaning the medication remains in the bloodstream longer, potentially causing prolonged side effects.

About 80% of sildenafil metabolites are excreted in feces and about 13% in urine. Severe renal impairment (CrCl below 30 mL/min) requires starting at 25 mg.

• Mild to moderate renal impairment: Standard dose generally acceptable
• Severe renal impairment: Start at 25 mg, adjust based on response
• Patients on dialysis: Close physician consultation required

If you have kidney concerns, bring blood test results when visiting an ED specialist clinic.

Patients taking antihypertensives face risk of excessive blood pressure reduction. Particular caution is needed with:

• Alpha-blockers (doxazosin, prazosin): Similar vasodilatory effect increases orthostatic hypotension risk. Start with sildenafil 25 mg and allow 4+ hours between doses.
• Calcium channel blockers (amlodipine): May enhance hypotensive effect, but clinically significant impact is generally low.
• ACE inhibitors/ARBs: Relatively safe for concurrent use, but physician disclosure is mandatory.

Taking antihypertensives does not automatically disqualify you from using sildenafil. In most cases, dose adjustment or timing modification allows safe use.

Not just prescription drugs — some OTC medications and supplements can also interact with sildenafil.

In particular, overseas male enhancement products have been found to contain undeclared PDE5 inhibitor ingredients, creating overdose risk when combined with sildenafil.

Patients aged 65 and older have been reported to have approximately 40% higher sildenafil blood levels compared to younger patients due to age-related physiological decline.

• Starting dose of 25 mg is recommended
• Dose adjustment needed considering hepatic/renal function decline
• Higher polypharmacy risk requires comprehensive medication review
• Cardiovascular comorbidities are common; exercise tolerance assessment is important

Many elderly patients safely use ED medications under proper medical evaluation. Age alone is not a reason to give up.

Diabetes is a major risk factor for ED, with approximately 50% of diabetic patients experiencing ED. Sildenafil is not contraindicated for diabetic patients and can generally be used safely.

However, note the following:

• Advanced diabetic neuropathy may reduce sildenafil’s effectiveness
• Advanced atherosclerosis requires cardiovascular risk assessment
• Diabetic nephropathy may require dose adjustment
• If efficacy is insufficient, switching to tadalafil (Cialis®) or vardenafil (Levitra®) may be considered

For diabetic patients, pursuing ED treatment alongside diabetes management is key. Our clinic proposes optimal ED medication considering your diabetic condition.

There are 3 PDE5 inhibitors, each with different characteristics. If side effects from sildenafil are problematic, switching may help.

Tadalafil (Cialis®) has a longer duration, allowing natural timing for sexual activity. See: tadalafil details.

Even if all PDE5 inhibitors are contraindicated, the following alternative treatments exist:

• ICI therapy (intracavernosal injection): Prostaglandin E1 injected directly into the penis. Different mechanism from PDE5 inhibitors, so it may be used under physician supervision even with nitrate use.
• Vacuum constriction device (VCD): Non-drug therapy using negative pressure to draw blood. No drug interaction risk.
• Testosterone replacement therapy: Effective for ED caused by low testosterone. May enhance PDE5 inhibitor effectiveness when combined.
• Psychological counseling: Effective for psychogenic ED cases.

The appropriate treatment depends on the cause of ED and comorbidities. Men’s Care Clinic ED specialists create personalized treatment plans for each patient.

When visiting an ED clinic, accurately providing the following information is key to safe prescribing:

• All current medications (including prescriptions, OTC drugs, and supplements)
• Past medical history (heart disease, cerebrovascular disease, liver/kidney disease, diabetes)
• Allergy history (prior drug hypersensitivity reactions)
• Previous ED treatment (history with other ED drugs, effects, side effects)
• Lifestyle habits (drinking frequency, smoking status)
• Recent health check results (blood pressure, blood test values)

By disclosing this information fully, your physician can accurately determine the optimal medication and dosage.

Men’s Care Clinic maintains a patient safety-first prescribing system.

ED medications available online carry serious risks:

• Counterfeit products: WHO surveys report approximately 50% of ED drugs sold by online pharmacies are counterfeit
• Harmful contaminants: Counterfeits have been found to contain methamphetamine, pesticides, and ink
• Inaccurate dosing: Actual active ingredient content may differ significantly from labels
• No physician safety check: Taking medication without contraindication screening can cause serious health consequences
• No adverse event compensation: Unlike properly prescribed medications, personal imports are not covered by pharmaceutical adverse reaction relief systems

For safe ED treatment, always obtain prescriptions from a medical facility. Online consultations allow you to see a doctor from home.

In most cases, well-controlled hypertension does not prevent sildenafil prescribing. However, dose adjustment may be needed with certain antihypertensives (especially alpha-blockers). Uncontrolled hypertension above 170/100 mmHg is contraindicated. Always inform your doctor of your specific antihypertensive medications.

If recovery is progressing well and you are not using nitrate medications, prescribing may be possible at your physician’s discretion. However, evaluation of the coronary artery disease that necessitated the stent and current exercise tolerance is required. If you carry nitroglycerin for emergency use, concurrent use is contraindicated.

Alcohol is not contraindicated, but heavy drinking can reduce sildenafil’s effectiveness and intensify side effects (headache, dizziness, hypotension). Generally, one medium beer (500 mL) is acceptable, but individual tolerance varies. We recommend starting with small amounts.

Sildenafil is not contraindicated for diabetic patients and can be prescribed. However, advanced diabetic neuropathy or vascular damage may reduce efficacy. In such cases, switching to tadalafil (Cialis®) or dose adjustment may be considered. Combining ED treatment with blood sugar management is most effective.

When properly evaluated and prescribed, the risk of cardiac arrest from sildenafil alone is extremely low. Reported cases of cardiac arrest were primarily associated with concurrent nitrate use or use despite meeting contraindication criteria. Following physician guidance and confirming no contraindications apply ensures safe use.

Among BPH medications, alpha-blockers (tamsulosin, silodosin) require caution when combined. This is not a contraindication, but sildenafil should start at 25 mg with 4+ hours between doses. 5-alpha-reductase inhibitors (dutasteride) are generally safe to combine.

Yes, they do. Generic sildenafil tablets contain the same active ingredient, so all contraindications, drug interactions, and side effect risks are identical to the brand-name product. Being generic does not change the safety profile. Always obtain genuine generics from a medical facility.

Contraindication criteria apply regardless of age. Even younger patients with congenital heart disease, retinitis pigmentosa, or severe hepatic impairment are contraindicated. Recreational use of amyl nitrite (“poppers”) is also a contraindication. Being young does not guarantee safety — always consult a physician.

It depends on the reason. The nitrate contraindication applies to ALL PDE5 inhibitors, so tadalafil and vardenafil cannot be used either. However, if the issue is sildenafil-specific side effects (visual disturbances), switching to tadalafil or vardenafil may help. Consult your physician.

If you experience chest pain, difficulty breathing, fainting, or an erection lasting more than 4 hours, seek emergency medical care immediately. Always inform medical staff that you have taken sildenafil. Mild headache and flushing are usually temporary, but consult your prescribing physician if symptoms persist.

1. Viagra (sildenafil) Prescribing Information — Pfizer / Viatris
2. Japanese Urological Association. ED Clinical Practice Guidelines, 3rd Edition (2018).
3. Kloner RA, et al. “Cardiovascular safety of phosphodiesterase type 5 inhibitors after nearly 2 decades on the market.” Sex Med Rev. 2018;6(4):583-594.
4. Schwartz BG, Kloner RA. “Drug interactions with phosphodiesterase-5 inhibitors used for the treatment of erectile dysfunction or pulmonary hypertension.” Circulation. 2010;122(1):88-95.
5. WHO — Substandard and falsified medical products fact sheet.