Reference
FAQ and medical glossary
Short answers a pharmacist would rather you have before the visit. They are not personal advice. Where a label is specific, the medication pages cite it.
Questions
Do these pills cause an erection by themselves?
No. They prolong the chemical signal that sexual stimulation starts. Without stimulation, little happens.
Can I take one if I use nitroglycerin only rarely?
No. Intermittent nitrate use is still a contraindication. That includes a spray you have not touched in months and nitrite poppers.
I have chest pain after a tablet. Can I use my nitroglycerin if several hours have passed?
Do not decide that at home. Call emergency services and tell them the drug and the time. For sildenafil and vardenafil the safe interval is not established. Tadalafil’s 48-hour figure and avanafil’s 12-hour figure are for monitored emergency care.
Is a 36-hour Cialis erection a thing?
No. The 36 hours is how long the drug may still help you respond to stimulation. An erection that is still present at 4 hours is an emergency on every drug in this class.
Can I take the daily tadalafil and an extra tablet later?
No. As-needed and once-daily regimens are alternatives. Combining them stacks the dose.
Why did sildenafil fail after a burger and fries?
A high-fat meal delays the peak by about an hour and lowers it by about 29 percent. The dose may arrive late and feel weak. A second tablet the same day is not the labeled fix.
Is generic sildenafil actually Viagra?
It is the same active ingredient when the generic is FDA-approved. The tablet may look different. A supplement is not a generic, even if testing would find sildenafil inside it.
What is the usual starting dose?
Labels, for many adults: sildenafil 50 mg, tadalafil 10 mg as needed or 2.5 mg daily, vardenafil 10 mg, avanafil 100 mg. Age, kidney and liver disease, and other drugs change the start. Your prescriber’s number overrides this sentence.
Can I split a 100 mg tablet to make 50 mg?
Only if the prescriber and pharmacist say that specific tablet is meant to be split. Some tablets are not scored, and pulmonary-hypertension 20 mg tablets are a different product.
Do these protect me from sexually transmitted infections?
No. Nothing in this drug class reduces infection risk. The labels say so.
Can women take them?
These products are not approved for female sexual dysfunction. Some sildenafil products are prescribed for pulmonary hypertension in women under a different label. That is a specialist use, not an ED tablet borrowed from a partner.
What if I also take tamsulosin?
Tell the prescriber. Alpha-blockers plus a PDE5 inhibitor can drop blood pressure. Labels start at a low ED dose and only after the alpha-blocker is stable. Do not time this yourself.
Are gas-station pills safer because they are herbal?
No. FDA keeps finding undeclared PDE5 inhibitors and analogues in them. The nitrate risk is the same, and the dose is unknown.
How do I know an online pharmacy is legitimate?
It requires a real prescription, holds a license you can confirm on a state board site, and can be matched to NABP’s own lists if it claims accreditation. A copied seal is not a license. Details are on the verification page.
Does ED mean I have heart disease?
Not always. Performance anxiety, medicines, hormones, and neurologic injury all cause it. When the pattern is gradual and morning erections have faded, blood vessels are a leading suspect, and the visit should include cardiovascular risk, not only a refill.
What if the first prescription does nothing?
Review timing, food, alcohol, stimulation, and anxiety with the prescriber before you change drugs. Some men need several attempts at an adequate dose. Some need a different treatment entirely, such as a vacuum device or alprostadil, especially after pelvic surgery.
Can I drink grapefruit juice to make the pill stronger?
No. Grapefruit inhibits CYP3A4 unpredictably. Raising the level on purpose is how side effects and blood-pressure drops happen. Ask before you combine them.
Glossary
- Bioavailability
- The fraction of a swallowed dose that reaches the bloodstream. Oral sildenafil averages about 41 percent.
- Cyclic GMP (cGMP)
- The messenger that relaxes smooth muscle in the penis and in blood vessels. Nitrates raise it. PDE5 breaks it down.
- CYP3A4
- A liver and gut enzyme that clears all four ED drugs in this guide. Inhibitors such as ketoconazole, ritonavir, and grapefruit raise drug levels.
- Endothelium
- The cell lining of blood vessels. It produces nitric oxide. Smoking, diabetes, and high blood pressure damage it.
- Generic
- An FDA-approved copy of a brand drug with the same active ingredient, strength, and dosage form, and with demonstrated bioequivalence. Not a synonym for “compounded,” “herbal,” or “foreign.”
- NAION
- Non-arteritic anterior ischemic optic neuropathy. A sudden loss of vision from poor blood flow to the optic nerve. Stop the drug and get same-day care if vision drops suddenly.
- Nitrate
- A nitric oxide donor such as nitroglycerin or isosorbide, used for angina and for some other conditions. Contraindicated with every PDE5 inhibitor.
- Nitric oxide
- A short-lived gas released by nerves and endothelium. It starts the erection signal and also relaxes systemic blood vessels.
- PDE5 inhibitor
- A drug that blocks phosphodiesterase type 5. Sildenafil, tadalafil, vardenafil, and avanafil are the four used for ED in the United States.
- Priapism
- On these labels, a painful erection lasting more than 6 hours. Patients are told to seek care at 4 hours, before that definition is met.
- Pulmonary arterial hypertension
- High blood pressure in the arteries of the lungs. Sildenafil and tadalafil are also used for it, at different doses and schedules than for ED.
- Tmax
- The time after a dose when blood concentration peaks. For fasting sildenafil the median is about 60 minutes. A high-fat meal pushes it later.