Pharmaceuticals/Chemicals Human RCT evidence

Tadalafil

Cialis

17.0 hours

Half-life

2.5–20 mg

Typical dose

Long-acting PDE5 inhibitor; also used off-cycle for BPH/endothelial support.

Key takeaways

PDE5 inhibitor approved for ED, BPH, and pulmonary hypertension; ~17-hour half-life.
Peaks ~2.5 hours post-dose; daily dosing reaches steady state in about 5 days.
Dataset bioavailability (~80%) is an estimate; the absolute value is unestablished in humans.
Absolute contraindication with nitrates; caution with alpha-blockers and stimulants.

Overview

What it is

Tadalafil (Cialis) is a phosphodiesterase-5 inhibitor approved for erectile dysfunction, benign prostatic hyperplasia, and pulmonary hypertension. It blocks the enzyme that degrades cGMP in smooth muscle, sustaining nitric-oxide-mediated vasodilation. The 17-hour half-life is what separates it from sildenafil.

Pharmacokinetics

Plasma peaks about 2.5 hours after a dose, the ~17-hour half-life covers a full day per dose, and steady state arrives within about 5 days on daily dosing. The dataset models ~80% bioavailability as an estimate; absolute oral bioavailability hasn't been formally established in humans.

What the evidence says

Approval rests on extensive randomized trials for ED and BPH, with the daily 5 mg dose backed for both. Low-dose daily use for endothelial or blood-pressure support in anabolic contexts is community practice, not an indication. The hard rule is pharmacological: never combine with nitrates, because the interaction can crash blood pressure.

Reported dosing protocols

Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.

Use case	Dose	Route	Frequency	Duration
Erectile dysfunction, on-demand (label)	10–20 mg	Oral	As needed, max 1×/day
ED / BPH, daily (label)	2.5–5 mg	Oral	Once daily	Chronic

Pharmacokinetic summary

Model tier: Advanced (t½ + Cmax + Tmax + F)
Half-life: 17.0 hours
Cmax: 1725 ng/mL
Tmax: 0.1 days
Bioavailability: 80%
Typical dose: 2.5–20 mg

Harm reduction

⚠ Tadalafil + clenbuterol or trenbolone compounds cardiovascular risk (tachycardia, BP). Monitor closely.

Frequently asked questions

Tadalafil vs sildenafil — what actually differs?

Duration. Sildenafil works for about 4–6 hours, tadalafil up to 36, which allows on-demand dosing without clock-watching or a low once-daily dose. Side-effect profiles overlap; back pain and muscle aches are more characteristic of tadalafil.

Is daily low-dose tadalafil for blood pressure or endothelial health legitimate?

It's approved for pulmonary hypertension at higher doses, and small studies show modest vascular effects, but prophylactic use in anabolic contexts is community practice without outcomes data. It also interacts with nitrates and stimulants, which matters in that setting.

Why is combining tadalafil with nitrates dangerous?

Both raise cGMP-mediated vasodilation, and together they can drop blood pressure precipitously, causing syncope or worse. The combination is an absolute contraindication on the label, and the long half-life extends the risky window after the last dose.

References

PMC tadalafil PK
Tadalafil pharmacokinetics in healthy subjects (Br J Clin Pharmacol 2006) — Human PK: 17.5-hour half-life, ~2.5-hour Tmax; absolute bioavailability not established.

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