What it is
Tadalafil is a long-acting PDE5 inhibitor, the same drug class as sildenafil but with a roughly 17.5-hour half-life, which is why it is the one used for daily low-dose protocols. The framing I was responding to is well-known: Bryan Johnson has said he takes 2.5 mg daily for longevity rather than erections, and on Andrew Huberman's show a low daily dose is discussed as something most men over 40 might consider for blood flow. Both are clear that this is personal practice, not a doctor prescribing for me.
Why I tried it
Two goals. First, general longevity and better blood flow, to see whether I could feel anything. Second, blood flow during weight training, which is why I timed the dose about two hours before lifting, trying to land near peak absorption.
The pre-workout timing, examined
For a single dose the timing is reasonable: peak plasma is around two hours, and unlike sildenafil, food does not blunt it. Two things undercut it for me. First, on a daily dose the drug accumulates to a flat steady state within about five days, so the previous days' doses are still working, and timing today's tablet two hours before the gym is essentially cosmetic once you are dosing every day. Second, the training benefit I was timing for is not well supported: the most on-point human trial gave healthy athletes tadalafil at 20 mg, eight times my dose, and found no change in VO2max or aerobic and anaerobic thresholds. The cleaner "restores muscle blood flow" data come from boys with Duchenne muscular dystrophy, where the nitric-oxide signaling pathway is broken; relieving that is a disease-model rescue, not evidence that healthy muscle gets extra flow. The popular "tadalafil pre-workout for pumps" idea is an extrapolation from that mechanism, carried mostly by telehealth marketing rather than any trial showing it works.
The side effect
The ache I felt is a recognized, dose-related effect, not a fluke. The prescribing information describes "diffuse bilateral lower lumbar, gluteal, thigh, or thoracolumbar muscular discomfort," typically starting 12 to 24 hours after a dose, and on a daily dose it builds with accumulation, which fits why it showed up on day three or four rather than day one. Here is the part that stopped me: the single most specific thing I felt, that the ache was worst lying down, is not a quirk of mine. It is written into the official prescribing information, which says the discomfort is "exacerbated by recumbency." The pain eased when I moved, returned when I sat, and was worst in bed, exactly as described. Patients in a Mayo Clinic forum thread describe the same signature, worst at rest and easing within a day or two of stopping.
Mechanism, still unsettled
The popular explanation is off-target inhibition of PDE11: tadalafil is only about 40-fold selective for its target over PDE11, versus roughly 1,000-fold for sildenafil and 9,300-fold for vardenafil, which fits why this ache tracks with tadalafil specifically. But that story has a real hole, because one tissue study found PDE11 protein is not detectable in human skeletal muscle. The more mundane alternative is plain vasodilation, more blood flow and mild fluid shift in muscle and paraspinal tissue, which would also explain why it is worse lying still. Diagnostic workups in the original trials found no actual muscle damage. The honest summary is a recognized effect with a genuinely unsettled mechanism.
Does the body adapt?
A common piece of advice is to push through for a week or two until it fades. It often does fade in reports, but no study proves the side effect actually desensitizes. And adapting to a side effect is not the same as the underlying perturbation stopping; it mostly means I stop noticing something that is still happening to my muscles. That is not the same as the cause going away, and it is not a trade I wanted to make for an optional compound.
Every other day
The other suggestion is intermittent dosing. The math is not simply half the benefit: about 38 percent of a dose remains at 24 hours and 15 percent at 48 hours, so levels swing more but never fully clear. The vascular benefit also splits in two, an acute part, blood flow while the drug is present, which off-days sacrifice, and a slower endothelial part. There is one small study where alternate-day tadalafil improved and sustained endothelial function, but it used 20 mg in higher-risk men and a surrogate marker, and nothing tests intermittent 2.5 mg. For my training goal specifically, the off-day is exactly when the acute effect is gone.
The longevity premise
The harder question is whether the benefit is even worth chasing. The mortality and longevity signals for tadalafil are all observational and heavily confounded, because men who fill and refill these prescriptions tend to be healthier and more active to begin with, and the large drug-repurposing screens are explicitly correlative. The one rigorous randomized trial on a tissue-protection endpoint, in Duchenne muscular dystrophy, was negative. So the longevity case is a plausible hypothesis, not an established benefit, which sets a low ceiling on how much side-effect cost it justifies.
Safety boundary
Tadalafil is a prescription medication with real interactions, most importantly with nitrates and alpha-blockers, and it is not a supplement. This page documents one person's short experiment and decision. It is not a protocol, a dose to copy, or sourcing guidance.
Sources
- Bryan Johnson (X) — the "2.5 mg daily for longevity, not erections" framing that prompted this.
- Andrew Huberman (YouTube) — low-dose daily tadalafil discussed for men over 40.
- Mayo Clinic Connect — patient thread on tadalafil muscle ache, including the worse-lying-down pattern.
- Cialis (tadalafil) prescribing information, DailyMed — pharmacokinetics and the "exacerbated by recumbency" muscle-pain description.
- Tadalafil, StatPearls — peak around two hours, roughly 17.5-hour half-life, food has no meaningful effect.
- Di Luigi et al., Int J Sports Med 2008 — tadalafil 20 mg did not change VO2max or thresholds in healthy athletes.
- Nelson et al., Neurology 2014 — PDE5 inhibition restores exercise muscle blood flow in Duchenne muscular dystrophy, a disease model.
- Weeks et al., Int J Impot Res 2005 — PDE5-over-PDE11 selectivity: about 40-fold tadalafil, 1,000-fold sildenafil, 9,300-fold vardenafil.
- Loughney et al., Int J Impot Res 2005 — PDE11 protein not detected in human skeletal muscle.
- Rosano et al., European Urology 2005 — alternate-day tadalafil improved and sustained endothelial function in higher-risk men (small, 20 mg).
- Tadalafil exposure and cardiovascular outcomes (PMC) — observational association with lower mortality and events, with the authors' confounding caveats.
- Victor et al., Neurology 2017 — phase 3 tadalafil trial in Duchenne muscular dystrophy was negative.