How these medications work
Sildenafil (Viagra) and tadalafil (Cialis) are phosphodiesterase-5 (5-PDE) inhibitors. They sustain levels of cyclic GMP in the penile corpora cavernosum, which helps men with erectile dysfunction achieve an erection in response to sexual stimulation. They do not work without arousal.
Sildenafil directions
- Starting dose is usually 50 mg, taken as needed before sexual activity.
- Can be taken with or without food — but it is most effective on an empty stomach.
- Fast-acting; typically taken about an hour before activity.
Tadalafil directions
- Longer duration of action than sildenafil.
- Starting dose is 2.5 mg daily, or 10 mg daily as needed.
- Can be taken with or without food; most effective on an empty stomach.
- May be used indefinitely. Daily use can be more effective than as-needed for improving erectile and endothelial function, and removes concerns about timing and onset.
Do not use if…
Serious interaction — nitrates Never combine 5-PDE inhibitors with nitrates in any form (e.g. nitroglycerin, isosorbide mononitrate or dinitrate), whether taken regularly or occasionally. This combination can cause severe, dangerous drops in blood pressure.
- You take riociguat (Adempas), a soluble guanylate cyclase stimulator.
- You have heart or vascular conditions that make sexual activity unsafe — these must be evaluated and treated by your personal physician first.
- You had a stroke or heart attack within the last 6 months — see your personal physician first.
Use caution with…
Tell your provider in the questionnaire if any of these apply. A lower starting dose may be appropriate, or treatment may not be recommended:
- CYP3A4 inhibitors (e.g. ketoconazole, erythromycin, ritonavir) — can increase side effects.
- CYP3A4 inducers (e.g. rifampin, carbamazepine, St. John’s wort) — can reduce effectiveness.
- Alpha blockers for blood pressure or enlarged prostate (e.g. tamsulosin, doxazosin) — risk of low blood pressure; a lower starting dose is used.
- Chronic kidney disease or dialysis — dosing is adjusted; tadalafil is avoided in CKD stage 4–5.
- Regular grapefruit juice — start at a lower dose.
Possible side effects
Most side effects are mild and temporary. They may include:
- Headache, flushing, indigestion or stomach burning
- Nasal congestion, runny nose, or nosebleeds
- Diarrhea, back or muscle aches
- A temporary bluish tinge to vision (more associated with sildenafil), usually resolving in 2–3 hours
- Sudden, usually one-sided hearing loss within 24 hours of use (often temporary)
Stop and get care for vision or hearing changes In men over 50 with high blood pressure or high cholesterol, there is a very rare risk of NAION (a serious eye condition), retinal detachment, or retinal vein occlusion. If you develop sudden vision or hearing symptoms, stop the medication and be evaluated promptly by a specialist.
What you agree to
- You will not combine sildenafil or tadalafil with dietary supplements that claim to boost sexual stamina, confidence, or performance, or that claim to contain prescription-strength sildenafil or tadalafil.
- If any concerning side effects develop, you will stop the medication and consult your physician.
Full manufacturer information
The complete manufacturer directions and warnings are available below. Read them in full before taking this medication.
View full manufacturer label (DailyMed)
A provider reviews every order This information does not replace medical advice. A licensed Louisiana provider reviews your questionnaire and confirms what’s safe and appropriate for you.