Four oral PDE5 inhibitors are FDA-approved in the United States for treating erectile dysfunction. Sildenafil came first in 1998 and changed the conversation around male sexual health overnight. Three others followed. The choice between them is not arbitrary — they differ meaningfully in onset, duration, food interactions, and side effects, even though they all work through the same mechanism. The right ED medications for any given man depend on lifestyle, comorbidities, and personal preference more than on raw potency.
How PDE5 Inhibitors Work
All four drugs block phosphodiesterase type 5, the enzyme that breaks down cyclic GMP in penile smooth muscle. By inhibiting the breakdown, they amplify the natural nitric-oxide-driven erection signal triggered by sexual stimulation. They do not cause spontaneous erections — sexual arousal is required for them to work. The AUA 2018 ED Guideline identifies PDE5 inhibitors as the first-line therapy for nearly all men with ED who do not have a contraindication.
The primary contraindication across the class is concurrent nitrate use. The combination can cause profound, life-threatening hypotension. Men taking nitrates for angina cannot use any PDE5 inhibitor. Concurrent use with alpha-blockers requires caution and dose separation. Men with severe cardiovascular disease, recent myocardial infarction or stroke, or unstable arrhythmia should be cleared by their cardiologist before starting therapy.
Sildenafil (Viagra)
Sildenafil typically begins working in 30 to 60 minutes and lasts 4 to 6 hours. It is dosed at 25, 50, or 100 mg taken on demand. A high-fat meal substantially delays and reduces absorption — many urologists recommend taking it on an empty stomach or with a light meal. Generic sildenafil has been available in the US since 2017 and now costs roughly $10 to $30 per dose through GoodRx pricing, dramatically less than the brand name. The FDA label describes a response rate of roughly 70% across the studied populations.
Common side effects include headache (16%), facial flushing (10%), nasal congestion, dyspepsia, and visual changes (typically a bluish tint to vision because of cross-reactivity with PDE6 in the retina). The visual effect is generally mild and transient.
Tadalafil (Cialis)
Tadalafil is the long-acting agent of the class. It begins working in 30 minutes and lasts up to 36 hours, which is why it is sometimes called “the weekender.” It is available in two dosing strategies: on-demand (10 or 20 mg) and daily (2.5 or 5 mg). Daily dosing maintains steady-state PDE5 inhibition and allows for spontaneous, unscheduled sexual activity. Tadalafil is uniquely also FDA-approved for benign prostatic hyperplasia, making it a logical choice for men with both ED and lower urinary tract symptoms.
Food does not meaningfully affect tadalafil absorption. Generic tadalafil has been available since 2018 and costs roughly $10 to $40 per on-demand dose, with daily 5 mg available for around $30 to $100 per month. Side effect profile is similar to sildenafil but with more back pain and muscle aches (4 to 7%) and fewer visual side effects since tadalafil has weaker PDE6 cross-reactivity.
Vardenafil (Levitra, Staxyn)
Vardenafil works similarly to sildenafil — onset in about 30 minutes, duration of 4 to 6 hours. It is available as a film-coated tablet (Levitra) and as an orally disintegrating tablet (Staxyn) that does not require water. Pharmacologically, vardenafil is more selective for PDE5 over other isoforms, which some clinicians believe gives a slightly lower rate of visual side effects.
Vardenafil has fallen out of favor commercially in the US. Brand-name production has been discontinued, although generics remain available. Pricing is similar to sildenafil. Vardenafil has a known QT-prolongation effect at higher doses and should be used cautiously in men taking class IA or III antiarrhythmics.
Avanafil (Stendra)
Avanafil is the newest of the four, FDA-approved in 2012. Its main advantage is rapid onset — clinical trials showed effective erections as early as 15 minutes after dosing. Duration is shorter, around 4 to 6 hours. It is dosed at 50, 100, or 200 mg.
Avanafil’s selectivity profile is more favorable in some respects: lower PDE6 cross-reactivity (fewer visual effects) and less PDE11 inhibition (less muscle aching). Side effects in trials were generally milder than sildenafil. The downside is cost — avanafil remains brand-name only in the US, and out-of-pocket costs typically run $50 to $80 per dose. Insurance coverage varies considerably.
Side Effects Across the Class
All four drugs share a similar side effect profile: headache, flushing, nasal congestion, dyspepsia, and back pain. Rare but serious adverse events include sudden hearing loss, non-arteritic anterior ischemic optic neuropathy (NAION), and priapism. Anyone experiencing sudden vision or hearing loss after taking a PDE5 inhibitor should stop the drug and seek immediate evaluation. For more on emergency erectile complications, see our priapism guide.
Who Each Drug Is Right For
For most new patients without strong preferences, generic sildenafil or generic tadalafil are the rational starting points based on cost and effectiveness. Men who want spontaneity and have at least 2 to 3 sexual encounters per week often prefer daily tadalafil. Men whose schedule allows planned use favor on-demand sildenafil. Tadalafil is the natural choice when BPH coexists. Avanafil is reasonable when rapid onset is preferred and cost is not a barrier, or when other PDE5 inhibitors caused intolerable side effects. For men who do not respond to oral therapy, second-line options include intracavernosal injections or a penile implant; shockwave therapy remains investigational.
Cost and Insurance Reality
Most commercial insurance plans cover generic sildenafil and tadalafil with prior authorization, often with a quantity limit (typically 4 to 6 doses per month). Brand-name and avanafil coverage is patchier. Medicare Part D covers the generics in many plans. Without insurance, GoodRx and pharmacy discount programs commonly bring sildenafil and tadalafil to under $1 per dose at certain pharmacies. Telehealth platforms such as Hims, Roman, and BlueChew bundle prescription and shipping at $30 to $80 per month for typical doses; convenience comes at a premium versus a local pharmacy. For a broader view of healthcare costs, see our healthcare costs guide.
Frequently Asked Questions
Which ED drug has the fewest side effects?
In head-to-head meta-analyses, avanafil and tadalafil tend to show slightly lower rates of headache and visual disturbance than sildenafil. Vardenafil sits between them. Individual response varies widely; the drug with the best side effect profile is the one a given patient tolerates best.
Can I take ED medication every day?
Daily low-dose tadalafil (2.5 or 5 mg) is FDA-approved for daily use. Sildenafil, vardenafil, and avanafil are designed for on-demand use, although off-label daily dosing is sometimes used. Daily PDE5 inhibition has been studied in cardiovascular and pulmonary conditions and appears safe in healthy men.
Does alcohol interfere with ED medication?
Modest alcohol intake (one to two drinks) does not meaningfully affect PDE5 inhibitor performance. Heavy alcohol use lowers libido, blunts erection quality, and may worsen the headache and flushing side effects. Combining heavy drinking with these drugs is not recommended.
Are online ED prescriptions safe?
Telehealth platforms operating with US-licensed clinicians and US-licensed pharmacies are generally safe. Foreign websites selling unprescribed sildenafil or “herbal” products with no prescription have been repeatedly flagged by the FDA for adulteration with unlisted ingredients. The price difference does not justify the risk.
The Bottom Line
Four FDA-approved oral medications cover the spectrum of needs: rapid onset, long duration, daily flexibility, low cost. Most men respond to one of the generics — sildenafil or tadalafil — and most do well at moderate doses. Switching agents when one is poorly tolerated is reasonable; abandoning oral therapy after one failed trial is not. Conversation with a primary care physician or urologist matches the right molecule to the right patient.