A small, well-studied PDE5 inhibitor used as preventative cardiovascular, cognitive, urinary, and erectile-health medicine — not as an on-demand pill. The Limitless rationale, dosing, and monitoring plan.
A protocol from Joshua Hare, DO · Founder & Medical Director
The position
Why we recommend it for most adult men on the Limitless protocol.
Tadalafil is best known as the on-demand erectile medication marketed under the trade name Cialis. The standing daily 5 mg dose is a different drug in clinical practice — and a far more interesting one. At low daily doses, tadalafil enhances nitric oxide signaling continuously, working on the same endothelial pathway that sits underneath nearly every age-related vascular condition. It is FDA-approved for daily use in benign prostatic hyperplasia (BPH) and erectile dysfunction, but its useful biology runs well beyond either indication.
For men in their 40s, 50s, and 60s — the demographic that fills most Limitless visits — daily tadalafil is one of the highest-leverage prescription tools we have for protecting endothelial, urinary, sexual, and probably cognitive function. It is generic, inexpensive, and well-tolerated by the great majority of patients.
"I do not prescribe daily tadalafil because patients ask for it. I prescribe it because the mechanism is the cleanest preventative move I can make on the endothelium, and the safety profile is excellent in the right patient. The sexual-function benefit is downstream of the same biology."
— Joshua Hare, DO · Medical Director
A second opinion
What Stanford and Huberman are saying.
This isn't a fringe protocol. The same recommendation has been echoed publicly by two of the most credible voices in performance and longevity medicine:
"Most men over 40 should probably be taking Cialis every single day. The vasodilation from it that helps with erections is the same mechanism that lowers blood pressure, protects the brain, and prevents strokes."
— Andrew Huberman, PhD · Stanford School of Medicine
Huberman was citing Dr. Mike Eisenberg, head of male sexual health at Stanford, who has publicly recommended 2.5 to 5 milligrams of tadalafil daily for most men over 40. The Limitless protocol uses the same dosing, the same indication, and the same underlying logic — endothelial NO signaling as a unifying preventative pathway.
This is mainstream academic medicine, not biohacker fringe. The mechanism is well-established, the molecule has been on the market since 2003, the generic is inexpensive, and the FDA has already approved daily 5 mg dosing for two indications. We are simply applying the same biology to a longevity-focused frame.
Read the evidence
Our physician-authored research summary walks through the unified-mechanism case — endothelial nitric oxide signaling as the substrate underneath cardiovascular, cognitive, urinary, erectile, and exercise capacity benefits — with primary-source citations. Daily tadalafil — one molecule, five systems →
Mechanism
Why the dose is 5 mg every day, not 20 mg on a Friday.
Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor. PDE5 breaks down cyclic GMP — the second messenger that dilates blood vessels in response to nitric oxide. Inhibit PDE5, and you allow the body's own nitric oxide signal to last longer and reach further. The smooth muscle of the penis is one place that signal acts, but it's the same signal that protects endothelial function in the coronary arteries, cerebral vessels, lower urinary tract, and peripheral vasculature.
Tadalafil's pharmacokinetics are what make it suitable for daily use:
Half-life of approximately 17.5 hours — by far the longest of the PDE5 inhibitors.
Steady plasma levels mean continuous endothelial support, not pulsed support — the difference between maintenance therapy and rescue therapy.
No food restriction. Onset is not the relevant variable on a daily protocol.
The on-demand 20 mg dose treats a symptom. The daily 5 mg dose treats a pathway. Those are clinically different uses of the same molecule.
Why we recommend it
Five reasons it earns a standing place on the protocol.
01 · Endothelial Function
The unifying mechanism
Daily PDE5 inhibition improves flow-mediated dilation — the standard measure of endothelial health — in healthy adults and in adults with cardiovascular risk factors. The endothelium is the single tissue that links nearly every age-related vascular condition: coronary disease, stroke, dementia, kidney decline, and erectile dysfunction. A drug that supports it daily is the closest thing we have to a vascular multivitamin.
02 · Cardiovascular Protection
Lower mortality signal
Multiple large observational cohorts in men with cardiovascular disease, type 2 diabetes, and post-MI status have found PDE5 inhibitor users had roughly 17–25% lower all-cause mortality, fewer incident heart failure events, and lower MACE (major adverse cardiovascular events). Observational, yes — but consistent across populations and biologically plausible given the mechanism.
03 · Cognitive & Cerebrovascular
An emerging Alzheimer's signal
Two large database studies (one in Nature Aging, one in BMJ Mental Health) found PDE5 inhibitor use was associated with substantially lower incidence of Alzheimer's disease in middle-aged and older men. Mechanism likely involves cerebral perfusion, glymphatic flow, and amyloid clearance. Not a treatment — but a preventative signal worth respecting in a long-acting daily medication.
04 · Urinary (BPH/LUTS)
FDA-approved indication
Daily 5 mg is FDA-approved for benign prostatic hyperplasia. It improves urinary flow, reduces nocturia, and lowers AUA symptom scores in men with prostatic enlargement. For men with both moderate BPH and any sexual-function concern, daily tadalafil is the single most efficient prescription answer.
05 · Erectile & Sexual Health
Preservation, not rescue
Daily 5 mg improves IIEF-5 scores, preserves nocturnal erections, and supports cavernosal smooth muscle health. In men with cardiovascular risk factors, post-prostatectomy patients, and patients on TRT, the daily protocol is associated with better long-term erectile preservation than waiting for symptoms to appear and rescuing on demand.
06 · Exercise & Recovery
Modest perfusion benefit
Improved peripheral perfusion translates into modest gains in exercise tolerance and recovery in some patients. Anecdotally common; the literature is thinner. We do not prescribe tadalafil for athletic performance, but it is a frequently-noticed side-benefit of the protocol.
The protocol
How we actually prescribe it.
Standing Daily Dose
Tadalafil 5 mg PO once daily
One tablet, every day, taken at any consistent time. Morning is fine; evening is fine. Food does not matter. Steady-state by approximately day 5.
Dose Adjustments
2.5 mg daily for selected patients
Used in moderate renal impairment, mild hepatic impairment, age 70+ at first prescription, or when a patient is also on a strong CYP3A4 inhibitor or an alpha-blocker (e.g. tamsulosin, doxazosin). The lower dose is also a reasonable starting point for any patient with a low baseline blood pressure.
Best fit for daily 5 mg
Adult men 35–75 with vascular risk factors (T2DM, hypertension, dyslipidemia, smoking history).
Men with BPH or moderate lower urinary tract symptoms.
Men on TRT who want to preserve erectile function long-term.
Post-prostatectomy patients in penile-rehabilitation phase.
Longevity-focused patients without contraindication who want a continuous endothelial-support agent.
Timeline of effect
What patients usually notice, and when.
Day 1–5
Steady-state plasma levels reached. Most patients notice nothing yet.
Week 1–2
First sexual-function changes — improved spontaneous and nocturnal erections.
Week 2–6
Urinary symptoms (frequency, nocturia, flow) noticeably improved in BPH patients.
Month 3+
Endothelial / vascular benefits accrue. Effect is biological, not subjective.
Safety profile
What to watch on this medication.
Tadalafil 5 mg daily is well-tolerated by the great majority of patients. The side-effect profile is dominated by predictable, dose-related, and usually transient effects of vasodilation. The serious risks are real but rare and predictable from a careful medication review.
Common, usually mild
Mild headache (most common, often resolves within 1–2 weeks).
Facial flushing.
Dyspepsia or mild reflux.
Back pain or myalgia (often muted at the 5 mg dose).
Nasal congestion.
Absolute contraindications — do not use
Concurrent organic nitrates — nitroglycerin (any form), isosorbide mono- or dinitrate, amyl nitrite ("poppers"). The combination can cause life-threatening hypotension. This is a hard line.
Severe hypotension or recent acute coronary syndrome — within the past 90 days.
Sudden hearing loss — stop the medication and seek evaluation.
NAION — sudden vision changes; stop the medication and seek evaluation.
Priapism (erection > 4 hours) — extremely rare at the 5 mg daily dose. Emergency.
Monitoring
How we follow the protocol.
Baseline: resting blood pressure, comprehensive metabolic panel (renal/hepatic function), lipid panel, complete medication review with focus on nitrates and alpha-blockers, and an IIEF-5 sexual function score where relevant.
Week 4–6: brief portal check-in for tolerability — headache, GI symptoms, blood-pressure stability.
Annually: medication reconciliation, blood pressure review, repeat any relevant baseline labs as part of the annual Limitless panel.
Stop criteria: any new prescription for organic nitrates; new ophthalmologic diagnosis (retinal disorder, NAION); intolerable headache or BP drop that doesn't resolve; patient preference.
FAQ
What patients ask before starting.
Is this just Cialis?
Same molecule, different use. The on-demand 20 mg pill treats a symptom; the daily 5 mg dose treats a pathway. We almost never use the on-demand dose in our protocols — daily is more useful, more predictable, and has a broader benefit profile.
Is it safe to take every day, indefinitely?
For most appropriately-screened patients, yes. The medication has been on the market since 2003; the safety database is large. The risks are dominated by drug interactions (nitrates) and a small number of rare-but-serious events that we screen for at baseline. We re-evaluate annually.
Will it interact with my testosterone protocol?
No — they are complementary. Patients on TRT often see better erectile and urinary outcomes when daily tadalafil is added, particularly in men with vascular risk factors.
Can my partner notice it?
Tadalafil is not transferred through skin contact or seminal fluid in clinically meaningful amounts. There is no concern for partners.
What does it cost?
Generic tadalafil 5 mg daily is inexpensive — typically $15–30 per month at most pharmacies, less with discount programs. Many HSA/FSA plans cover it.
Is the cognitive / Alzheimer's data definitive?
No — it is observational and the effect size has varied across studies. We don't prescribe tadalafil to prevent Alzheimer's. We prescribe it for endothelial, cardiovascular, urinary, and sexual-health benefit, and we view the cognitive signal as a plausible bonus that should be replicated in randomized trials.
What if I forget a dose?
Take it when you remember the same day, then resume your normal schedule. Don't double up.
Want this on your protocol?
Daily tadalafil 5 mg is a standard part of the Limitless adult-male longevity protocol when no contraindication is present. We screen at intake, prescribe through a licensed pharmacy, and follow as outlined above.
This page is for educational purposes and does not constitute medical advice. Tadalafil is a prescription medication; treatment decisions are made on an individual basis after evaluation by Joshua Hare, DO. Daily tadalafil 5 mg is FDA-approved for the treatment of erectile dysfunction and benign prostatic hyperplasia; its use for endothelial, cardiovascular, and cognitive support reflects clinical extrapolation from mechanism and observational evidence and is not an FDA-approved indication. Last reviewed May 3, 2026.