This page describes pharmacological agents that may have legal restrictions, side effects, and drug interactions in your jurisdiction. Information is for educational research only — consult a clinician before considering any compound.

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Tadalafil

Well Researched

Long-half-life PDE5 inhibitor (17.5 hr) that turns into a smooth daily background vasodilator at 2.5-5 mg — the only PDE5i where "low-dose…

Aliases (16)

Cialis · Adcirca · Tadacip · Tadarise · Megalis · Tadora · (6R,12aR)-6-(1,3-benzodioxol-5-yl)-2-methyl-2 · 3 · 6 · 7 · 12 · 12a-hexahydropyrazino[1 · 2':1 · 6]pyrido[3 · 4-b]indole-1 · 4-dione

TYPICAL DOSE

2.5-5 mg

Daily

ROUTE

Oral (tablet)

Oral

CYCLE

None required. Daily indefinite use is FDA-appr…

As prescribed

STORAGE

Room temp; original container

Room temp

Overview

What is Tadalafil?

Tadalafil is a long-acting PDE5 inhibitor approved by the FDA for erectile dysfunction, benign prostatic hyperplasia, and pulmonary arterial hypertension. Its long half-life (~17.5 hours) allows once-daily dosing and earned it the "weekend pill" nickname versus sildenafil.

Key Benefits

Treats erectile dysfunction with up to 36-hour duration, improves urinary symptoms in BPH, supports endothelial function and blood flow, and used off-label to enhance exercise performance and recovery via improved circulation.

Mechanism of Action

Inhibits phosphodiesterase type 5 (PDE5), preventing the breakdown of cyclic guanosine monophosphate (cGMP). Elevated cGMP causes smooth muscle relaxation in penile and pulmonary vasculature, leading to enhanced blood flow following sexual stimulation or pulmonary vasodilation in PAH.

▸Brand options6 known

CialisAdcircaTadacipTadariseMegalisTadora

StatusRx (US), POM (UK), Rx most jurisdictions; not scheduled

Research Indications

Most Effective

Pulmonary vasculature

basis for Adcirca/PAH approval at 40 mg daily.

Effective

Prostatic and bladder smooth muscle

basis for BPH approval (Cialis 5mg daily).

Investigational

Systemic peripheral vasculature

modest BP drop (~5 mmHg systolic).

Investigational

Cerebral vasculature

present, mechanism for the cognitive blood-flow hypothesis.

Investigational

Skeletal muscle and mitochondria

emerging area; PDE5 inhibition appears to support mitochondrial biogenesis and endothelial function in trained muscle.

Peptide Interactions

citicoline:

Synergistic

Theoretical complement — citicoline supports endothelial function and ACh-driven NO release; tadalafil amplifies the resulting vasodilation. No RCT but mecha…

methylene-blue:

Synergistic

Both touch NO/cGMP signaling but at *different* nodes — MB at low dose is a soluble guanylate cyclase modulator with mitochondrial effects; tadalafil downstr…

l-citrulline / l-arginine:

Synergistic

Direct NO precursors. Stack adds substrate to the NO arm of the same pathway tadalafil amplifies. Generally safe, mild additive BP effect.

agmatine:

Synergistic

NO modulator + nNOS inhibitor balance — theoretical complement for vascular cognitive flow.

beta-alanine, taurine, creatine:

Synergistic

Neutral; tadalafil doesn't interfere with any of these.

Nitrates (any form — nitroglycerin, isosorbide, "poppers"/amyl nitrite):

Avoid

ABSOLUTE CONTRAINDICATION. Severe, potentially fatal hypotension. No exceptions. Includes recreational poppers.

Alpha-blockers (tamsulosin, doxazosin, terazosin):

Avoid

Caution — additive hypotension. Spaced dosing and lower starting dose required if combined. Not relevant for users in this archetype.

Riociguat (Adempas) and other sGC stimulators:

Avoid

Contraindicated; redundant pathway hit.

Strong CYP3A4 inhibitors (ketoconazole, ritonavir, clarithromycin):

Avoid

Reduce tadalafil dose by 50-75% or avoid; AUC can rise 3-5×.

Strong CYP3A4 inducers (rifampin, carbamazepine, St. John's Wort):

Avoid

Significantly reduce exposure; clinical efficacy compromised.

Heavy alcohol (>5 drinks):

Avoid

Additive vasodilation/orthostasis; mild-moderate intake is fine.

Quality Indicators

✓

Pharmacy-dispensed, intact packaging

Prescription tablets in original sealed packaging from a licensed pharmacy.

Generic vs branded

Generics are usually fine but bioavailability can vary slightly; track if you switch.

✗

Unbranded blister or counterfeit risk

Counterfeit pharmaceuticals are a known issue; verify pharmacy and lot if buying internationally.

What to Expect

Day 1
PK-driven acute peak per administration. Verify dose tolerated.
Week 1
Steady-state reached for most daily-dosed pharma.
Week 2-4
Therapeutic effect established; titration window if needed.
Long-term
Periodic monitoring per drug class (labs, BP, ECG as applicable).

Side Effects & Safety 8

Side Effects

1Headache (10-15% at 5 mg daily, higher at PRN doses) — usually first 1-2 weeks then attenuates
2Back pain / myalgia (5-12%) — PDE11 cross-reactivity; often dose-dependent
3Dyspepsia / reflux (5-10%)
4Nasal congestion (3-7%)
5Flushing (2-5%)
6Limb pain
7Mild visual disturbance (less common with tadalafil than sildenafil due to lower PDE6 affinity)
8Dizziness, especially on standing (orthostatic)

When to Stop

NAION (non-arteritic anterior ischemic optic neuropathy) — sudden vision loss in one or both eyes. Rare but irreversible. Stop immediately and seek ophthalmology if any sudden visual changes. Risk factors: small optic disc cup, age >50, diabetes, smoking, prior NAION. the user's risk is essentially baseline-low.
Sudden sensorineural hearing loss — very rare; same protocol (stop and seek ENT).
Priapism (erection >4 hours) — extremely rare with tadalafil specifically (more common with intracavernosal therapies). ER if it occurs.
Severe hypotension — only relevant with nitrates, alpha-blockers, or volume depletion.
First 2 weeks: headache and back pain often appear and then attenuate. If they don't attenuate by week 4, drop to 2.5 mg or stop.
First 8 weeks: any vision change → stop immediately and consult ophthalmology.
Ongoing: monitor resting BP; tadalafil can drop systolic ~5 mmHg.