Among the four FDA-approved oral medications for erectile dysfunction, avanafil (Stendra) has the lowest rates of common side effects based on clinical trial data. That said, all four drugs in this class work through the same mechanism and share a strong overall safety record. The “safest” choice depends on your specific health profile, other medications you take, and how you plan to use treatment.
How These Drugs Work
All four oral ED medications belong to a class called PDE5 inhibitors. They work by relaxing blood vessels in the penis, allowing more blood flow during arousal. The four options are sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra), and avanafil (Stendra). They differ in how long they last, how quickly they kick in, and how precisely they target the enzyme involved in erections versus similar enzymes elsewhere in the body. Those differences in precision are what create the gap in side effect rates.
Why Avanafil Has the Fewest Side Effects
Every PDE5 inhibitor is designed to block a specific enzyme called PDE5, but they also accidentally affect related enzymes in other tissues. When a drug blocks PDE6 in the retina, you get visual disturbances like blue-tinted vision. When it blocks PDE1 in blood vessels, you get headaches and facial flushing. When it blocks PDE11 in muscle tissue, you get back pain and muscle aches.
Avanafil is far more selective than the older drugs. It’s 120 times more selective against the retinal enzyme compared to sildenafil’s 16-fold selectivity. It’s over 10,000 times more selective against the blood vessel enzyme compared to sildenafil’s 380-fold selectivity. And it’s over 19,000 times more selective against the muscle enzyme compared to tadalafil’s 25-fold selectivity. In plain terms, avanafil mostly hits its intended target and leaves other tissues alone.
The clinical numbers reflect this. At its highest dose (200 mg), avanafil causes headache in 9.3% of users, compared to 12.8% for sildenafil, 14.5% for tadalafil, and 16% for vardenafil. Flushing occurs in just 3.7% of avanafil users versus 10.4% for sildenafil and 12% for vardenafil. Visual disturbances are essentially absent with avanafil, while sildenafil and vardenafil both cause them in roughly 2% of users. Back pain and muscle aches occur in under 2% of avanafil users, compared to over 6% for tadalafil.
Tadalafil’s Strong Long-Term Safety Record
Tadalafil is the only ED drug approved for daily low-dose use (5 mg), which makes it popular for men who want spontaneity rather than planning around a pill. Its long-term safety has been studied more thoroughly than the others because of this daily dosing pattern.
In open-label extension studies lasting one and two years, daily tadalafil at 5 mg produced no serious adverse events that investigators attributed to the drug. No deaths or serious cardiovascular events were linked to the medication. The most common side effects at the 5% threshold were indigestion, headache, and back pain, all of which are considered mild. No meaningful changes showed up on heart monitoring or blood work over the full study period, representing over 350 patient-years of cumulative exposure.
Over 94% of participants in these studies remained compliant with their daily dose, which suggests the side effects were tolerable enough that nearly everyone stuck with treatment. For men who prefer daily dosing, tadalafil has the most reassuring long-term data available.
Risks That Apply to All PDE5 Inhibitors
Regardless of which drug you take, certain safety rules apply across the board.
The most critical is the interaction with nitrate medications, commonly prescribed for chest pain (nitroglycerin, isosorbide). Combining any PDE5 inhibitor with nitrates can cause a dangerous drop in blood pressure. This is an absolute rule, not a precaution. If you use nitrates in any form, including recreational poppers (amyl nitrite), PDE5 inhibitors are off the table.
Rare but serious events include a type of sudden vision loss called non-arteritic anterior ischemic optic neuropathy (NAION) and sudden hearing loss. These are noted across all four drugs. Men with a specific eye anatomy sometimes described as a “crowded disc” may face higher risk of the vision issue, and anyone with a prior episode should use extra caution.
Priapism, an erection lasting four or more hours that requires emergency treatment, is often cited as a risk but is extremely uncommon with oral medications. Since 1998, only 411 cases of priapism linked to Viagra, Cialis, or Levitra have been reported to the FDA, accounting for just 0.7% of all adverse drug reactions for these medications. Oral PDE5 inhibitors were responsible for only 2.9% of all drug-induced priapism cases, with injectable ED treatments carrying a far higher risk.
How Your Health Profile Affects the Choice
The safest drug for you personally depends on what else is going on in your body. Men with kidney problems, even severe impairment, generally don’t need dose adjustments for sildenafil. Mild to moderate liver disease also doesn’t require changes, though severe liver disease hasn’t been well studied with most of these drugs.
If you take alpha-blockers for an enlarged prostate, your doctor will likely start you on a lower dose of whichever PDE5 inhibitor you choose, since both drug types lower blood pressure. Tadalafil’s long duration (up to 36 hours) can be an advantage or a drawback depending on your other medications, because any side effects will last longer too. Avanafil’s shorter duration means side effects clear your system faster.
Men with cardiovascular disease aren’t automatically excluded from using these drugs. In fact, PDE5 inhibitors don’t increase heart attack risk in most men with stable heart conditions. The concern is about exercise tolerance: if you’re healthy enough for sexual activity, you’re generally healthy enough for the medication.
Choosing Between Safety and Convenience
The American Urological Association doesn’t rank one PDE5 inhibitor above another as a universal first choice. Their guidelines emphasize shared decision-making, where you and your doctor weigh the tradeoffs together. All four drugs are considered valid starting points.
In practice, the decision often comes down to balancing side effect profile against lifestyle preferences. Avanafil has the cleanest side effect numbers but works for a shorter window. Tadalafil has more side effects per dose but offers the longest duration and the strongest long-term data for daily use. Sildenafil has been on the market since 1998, giving it the deepest real-world safety track record, and it’s now available as an inexpensive generic. Vardenafil falls in the middle on most measures.
If minimizing side effects is your top priority, avanafil is the strongest option by the numbers. If you want a daily pill with proven long-term safety and the flexibility of not timing doses around sex, tadalafil at 5 mg daily is well supported by the evidence. If cost matters most, generic sildenafil is the practical winner and remains safe and effective for the vast majority of men.