Both tadalafil and sildenafil block PDE5 and improve endothelial function. But their pharmacokinetics, cardiovascular evidence base, and practical utility for longevity are meaningfully different. Here is how to think about the choice.
PDE5 inhibitors as a class have a strong cardiovascular and longevity rationale. The mechanism — blocking the enzyme that degrades cGMP and thereby sustaining nitric oxide signaling throughout the vascular system — applies equally to tadalafil and sildenafil.
But tadalafil and sildenafil are not interchangeable for longevity purposes. Their pharmacokinetics are fundamentally different, and that difference has direct implications for which compound makes more sense as a daily cardiovascular maintenance protocol.
This is the comparison that matters.
Sildenafil
Tadalafil
For endothelial function and cardiovascular protection, the mechanism requires continuous PDE5 inhibition — not an acute 4-hour window. Tadalafil's pharmacokinetics fit continuous endothelial maintenance; sildenafil's do not without multiple daily doses.
This is not a pharmacological opinion. It is reflected directly in how the drugs are licensed: tadalafil has a once-daily indication; sildenafil does not. The daily-dose tadalafil protocol studied in the clinical trials is a product of this pharmacological property.
Both tadalafil and sildenafil inhibit PDE5 with high selectivity — they share the same receptor target. Both increase cGMP, both sustain nitric oxide signaling, both produce vasodilation.
The key difference in selectivity: sildenafil has slightly higher inhibitory activity against PDE6 (expressed in retinal photoreceptors) and PDE1. This is why sildenafil can occasionally cause mild visual disturbances (blue-tinged vision, increased light sensitivity) at higher doses — an effect rarely if ever reported with tadalafil at longevity doses.
Tadalafil has slightly higher affinity for PDE11, expressed in skeletal muscle and testicular tissue. At 5 mg daily, PDE11 inhibition is modest and the clinical significance is considered low — some users report increased muscle fullness or subtle changes in exercise recovery that may relate to skeletal muscle vasodilation.
For cardiovascular longevity purposes, these selectivity differences are minor. The dominant clinical distinction is pharmacokinetic.
Both tadalafil and sildenafil appear in the major 2024 outcome studies:
TriNetX 2024 (Am J Med): 50 million US patients. Studied both tadalafil and sildenafil — and found benefit for both compounds on mortality, cardiovascular disease, and dementia. This confirms the class effect: PDE5 inhibition as a mechanism benefits the cardiovascular system regardless of which compound.
Kloner et al. 2024 (Clinical Cardiology): Tadalafil-specific. Found dose-dependent MACE and mortality reduction with hazard ratios as low as 0.40 for highest cumulative tadalafil exposure.
Soulaidopoulos et al. 2024 (Eur Heart J Cardiovasc Pharmacother): Meta-analysis of PDE5 inhibitors as a class. 22% MACE reduction, 30% all-cause mortality reduction.
The endothelial RCT data (FMD improvement, NO/endothelin-1 changes) is more extensive for tadalafil, largely because the once-daily dosing makes study design cleaner — you know exactly what plasma levels subjects are maintaining throughout the study period.
Sildenafil went generic in 2017. It is now one of the cheapest medications in any pharmacy. A 20 mg sildenafil tablet (the lowest commercially available dose, used for PAH) can cost under $0.50. Splitting a 100 mg tablet (which is how most people get cheap generic sildenafil) brings the per-dose cost very low.
However: using sildenafil as a longevity tool requires multiple daily doses (typically 25–50 mg two to three times daily) to approximate the continuous plasma levels tadalafil achieves with a single 5 mg dose. The side-effect profile (headache, flushing, potential visual effects) at the cumulative daily dose required is meaningfully worse than tadalafil's at 5 mg once-daily.
Compounded generic tadalafil has significantly closed the cost gap. At legitimate compounding pharmacies, 5 mg daily tadalafil is available for $30–60 per month — or $1–2 per day. This makes cost less of a differentiating factor than it was 5 years ago.
The direct comparison most relevant to longevity is the Aversa et al. 2021 trial (PMID 33818935): daily tadalafil 5 mg versus sildenafil 20 mg on-demand in men with ED and cardiovascular comorbidity. The outcome was endothelial biomarkers — NO, endothelin-1, vascular stiffness, flow-mediated dilation.
Daily tadalafil 5 mg was superior to sildenafil 20 mg on-demand on every endothelial measure. This is a pharmacokinetic effect, not a molecular one: continuous PDE5 inhibition from daily tadalafil produced better endothelial outcomes than the peak-and-trough profile of on-demand sildenafil.
A properly designed head-to-head trial of daily tadalafil 5 mg versus daily sildenafil 25 mg (a dosing schedule that would be closer to pharmacokinetically equivalent) does not exist in published form. The comparison above is the best available data.
For longevity and cardiovascular maintenance, tadalafil 5 mg once daily is the standard protocol for a reason:
1. Pharmacokinetics support continuous vascular benefit: Once daily produces stable plasma levels. Sildenafil would require multiple daily doses for the same effect.
2. Better-established daily-dose evidence base: The endothelial RCTs and the daily-dose FDA approval (for BPH) are specific to tadalafil.
3. Milder side-effect profile at the effective daily dose: 5 mg tadalafil once daily is better tolerated than the sildenafil dosing required for equivalent coverage.
4. Compounded generic makes cost comparable: The sildenafil cost advantage has significantly narrowed with compounded generic tadalafil availability.
Sildenafil has a role — in PAH (FDA-approved), as on-demand therapy for sexual function, and potentially in populations where the specific sildenafil data is most relevant. As a daily cardiovascular longevity tool, tadalafil is the better-supported choice.
Tadalafil daily protocol:
Sildenafil if you choose it:
PDE5 inhibitors as a class reduce cardiovascular events and all-cause mortality in the available data. That class benefit applies to both tadalafil and sildenafil.
For a daily continuous vascular maintenance protocol — which is the longevity application — tadalafil at 5 mg once daily is better matched to the mechanism and better supported by the clinical evidence. Its pharmacokinetics were designed for daily dosing. Sildenafil's were not.
If you are using either compound for longevity purposes, do so under physician supervision, respect the nitrate contraindication absolutely, and track your resting blood pressure to monitor your vascular response.
Can I switch from sildenafil to tadalafil?
Yes — they are in the same drug class and there is no washout period needed. Switching from as-needed sildenafil to daily tadalafil is a common change made in longevity practice. Start tadalafil at 2.5 mg for the first 2 weeks before moving to 5 mg.
Does tadalafil lose effectiveness over time?
There is no evidence of pharmacological tolerance to tadalafil at the 5 mg daily dose from the clinical literature. Some long-term users report consistent effects over years. If efficacy appears to diminish, consider whether blood pressure has changed, weight has changed, or other cardiovascular risk factors have worsened — these would affect the baseline from which tadalafil works.
What if I want sildenafil for on-demand use and tadalafil daily?
Do not combine two PDE5 inhibitors. If you are on daily tadalafil, you already have continuous PDE5 inhibition. Adding on-demand sildenafil is redundant pharmacologically and increases the risk of additive hypotension.
Is vardenafil a viable alternative?
Vardenafil (Levitra) is a third PDE5 inhibitor with a half-life of ~4–5 hours — similar to sildenafil. The same pharmacokinetic argument applies: it is not well-suited to once-daily dosing for continuous endothelial benefit. The longevity literature is focused on tadalafil for this reason.