What the PDE5 inhibitor trials actually show
Sildenafil, tadalafil, vardenafil, and avanafil, synthesized in one place: the cleanest evidence base of any category CitedRx covers, with no compounding ambiguity and nearly three decades of post-marketing safety data.
The trial landscape
| Drug | Approved | Key finding | Source |
|---|---|---|---|
| Sildenafil (Viagra) | 1998 | Pivotal trials (21 placebo-controlled studies, 3,000+ patients): 69% of intercourse attempts successful on sildenafil vs. 22% on placebo; mean IIEF erectile-function score rose from 15 to 22.4-25.0 depending on dose, vs. 16.6 for placebo. | PMC review |
| Tadalafil (Cialis) | 2003 | Integrative analysis of 5 RCTs; 81% of patients on 20mg reported improved erections at 12 weeks. Half-life ~17.5 hours (vs. sildenafil's ~4), giving an effective window of up to 36 hours. Once-daily low-dose (2.5mg/5mg) approved 2008. | FDA label |
| Vardenafil (Levitra) | 2003 | Same drug class and mechanism; less commonly prescribed today but remains FDA-listed as not withdrawn for safety or effectiveness reasons. | Federal Register |
| Avanafil (Stendra) | 2012 | The first new ED drug approved in nearly a decade at the time; positioned as faster-onset. Least commonly prescribed of the four today. | FDA approval letter |
| Class-wide safety | 2024 meta-analysis | 16 studies, >1.2 million subjects, median follow-up 4.3 years: PDE5 inhibitor use associated with lower risk of major adverse cardiovascular events and all-cause mortality, not merely neutral. Nitrate co-use remains contraindicated. | PMC / Eur Heart J |
The 69%/22% sildenafil figure is drawn from a secondary review citing the original pivotal trial data; we recommend treating it as high-confidence but secondary-sourced pending direct access to the original 1998 publication.
Sildenafil vs. placebo, visualized
What this means in plain language
Both drugs work: duration is the real choice
Sildenafil and tadalafil show similar efficacy in trials. The practical decision isn't "which works better," it's "which duration fits your life": sildenafil's shorter window suits planned use, tadalafil's much longer window (and daily option) suits spontaneity.
Generic isn't a downgrade
Unlike compounded GLP-1s, FDA-approved generic sildenafil and tadalafil are the exact same drug tested in the pivotal trials, made by a different (FDA-regulated) manufacturer. Compounded ED products (custom doses, combination pills, flavored chewables) are a genuinely different category, not individually FDA-reviewed.
The cardiovascular fear is largely outdated
Early PDE5 inhibitor safety data was mixed and fueled lingering hesitancy. The 2024 meta-analysis of over a million men found the opposite of a risk signal: lower cardiovascular events and mortality in PDE5 inhibitor users. The one real, unchanged contraindication is concurrent nitrate use.
Decision framework
| Your priority | What the evidence supports |
|---|---|
| Spontaneity, not planning around a dose | Tadalafil: its ~36-hour window is the trial-supported differentiator. |
| Lowest cost / most generic history | Sildenafil has the longest generic track record, typically the cheapest option. |
| Daily, low-dose option instead of as-needed | Tadalafil has an FDA-approved once-daily 2.5mg/5mg regimen. |
| Cardiovascular safety concerns | The 2024 meta-analysis (>1.2M subjects) is reassuring for the class: still avoid if taking nitrates. |
How this should shape which provider you choose
Every provider on our rankings page offering FDA-approved sildenafil or tadalafil (brand or generic) is dispensing the exact product tested in the trials above. Compounded products (custom combination doses, flavored chewables) are not individually FDA-reviewed, even when built on the same active ingredients. In September 2025, the FDA issued a warning letter to BlueChew's parent company specifically over claims that its compounded products contain the "same active ingredients" as brand drugs, finding that framing misleading.
Sources
- Sildenafil: from angina to erectile dysfunction to pulmonary hypertension (PMC review)
- FDA: Cialis (tadalafil) prescribing information
- Eli Lilly: FDA Approves Cialis for Once-Daily Use (2008)
- Long-term effects of PDE5 inhibitors on cardiovascular outcomes and death (PMC, 2024)
- Princeton IV Consensus Conference summary
- Federal Register: Levitra (vardenafil) determination
- FDA approval letter: Stendra (avanafil), 2012
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