Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CIALIS vs FINASTERIDE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Phosphodiesterase-5 (PDE5) inhibitor; increases c GMP levels, causing smooth muscle relaxation and vasodilation in the corpus cavernosum, enhancing erectile function.
Finasteride is a competitive 5-alpha-reductase inhibitor that prevents conversion of testosterone to dihydrotestosterone (DHT), thereby reducing DHT levels in serum and prostate tissue.
Treatment of erectile dysfunction,Treatment of benign prostatic hyperplasia,Treatment of pulmonary arterial hypertension (as Adcirca)
Benign prostatic hyperplasia (BPH),Male pattern baldness (androgenetic alopecia)
Tadalafil 10 mg or 20 mg orally as needed at least 30 minutes before sexual activity; maximum dosing frequency once daily. Alternative: 2.5 mg or 5 mg once daily for daily use.
1 mg orally once daily for androgenetic alopecia; 5 mg orally once daily for benign prostatic hyperplasia.
The terminal elimination half-life of tadalafil is approximately 17.5 hours in healthy subjects, which supports once-daily dosing for erectile dysfunction and once-daily use for benign prostatic hyperplasia. This long half-life distinguishes it from other PDE5 inhibitors.
Terminal elimination half-life is approximately 6-8 hours (range 4-12 hours) in young adults; prolonged to ~8 hours in elderly due to reduced clearance; clinical effect on DHT suppression persists for 24 hours post-dose.
Primarily hepatic via CYP3A4; minor pathways include CYP2C9 and glucuronidation.
Metabolized primarily via CYP3A4 in the liver; two inactive metabolites (t-butyl side chain oxidation and glucuronide conjugate).
Following oral administration, tadalafil is predominantly eliminated by hepatic metabolism. The metabolites are excreted mainly in feces (approximately 61% of the dose) and to a lesser extent in urine (approximately 36% of the dose). No unchanged parent drug is detected in urine.
Renal (39% as metabolites, <0.1% as unchanged drug); fecal (57% as metabolites); biliary elimination contributes to fecal route.
Tadalafil is 94% bound to plasma proteins, primarily to albumin. The protein binding is independent of drug concentration over a wide range.
Approximately 93% bound to plasma proteins (primarily albumin and to a lesser extent alpha-1-acid glycoprotein).
The apparent volume of distribution (Vd/F) is approximately 63 L (or roughly 0.9 L/kg for a 70 kg individual), indicating distribution into tissues beyond the vascular space, including the penis and other target organs.
Volume of distribution = 76 L (approximately 1.0-1.1 L/kg), indicating extensive tissue distribution; crosses blood-brain barrier and partitions into seminal fluid.
Absolute oral bioavailability of tadalafil has not been formally determined; however, the drug is well absorbed after oral administration, with peak plasma concentrations reached in 0.5 to 6 hours (median 2 hours). Food does not affect the extent of absorption (AUC), though it may delay the rate (Tmax) by about 1–2 hours.
Oral bioavailability is approximately 63% (range 50-80%) due to incomplete absorption and first-pass metabolism; food does not significantly affect bioavailability.
Cr Cl 30-50 m L/min: 5 mg once daily (max) for daily use; as-needed dosing: 10 mg not to exceed once every 48 hours. Cr Cl <30 m L/min: not recommended. Hemodialysis: not studied.
No dose adjustment required for any level of renal impairment including end-stage renal disease.
Child-Pugh A and B: no dose adjustment necessary for as-needed dosing; daily use: caution, start at 5 mg once daily. Child-Pugh C: not recommended.
No formal studies in hepatic impairment. Caution advised; use not recommended in severe hepatic impairment due to potential accumulation. No specific Child-Pugh based dose recommendations.
Not indicated for pediatric patients under 18 years.
Not indicated in pediatric patients. Safety and efficacy not established. Avoid use in children.
No dose adjustment required solely based on age; consider renal function and concomitant medications.
No age-related dose adjustment necessary. Monitor for adverse effects (e.g., sexual dysfunction, mood changes) due to potential increased sensitivity.
None
No FDA black box warning.
Risk of hypotension with vasodilators or alpha-blockers,Contraindicated with nitrates due to severe hypotension risk,Patients with left ventricular outflow obstruction (e.g., aortic stenosis) should avoid use,Caution in patients with hypotension, severe hepatic impairment, or end-stage renal disease,Risk of priapism: advise immediate medical attention for erections lasting >4 hours,Decreased visual or hearing ability requiring discontinuation
Risk of high-grade prostate cancer (decreased PSA levels may mask detection),Sexual adverse effects (e.g., decreased libido, erectile dysfunction, ejaculatory disorder) may persist after discontinuation,Increased risk of mood disturbances including depression and suicidal ideation,Not indicated for use in women or children; avoid handling crushed tablets during pregnancy due to risk to male fetus
Concomitant use of nitrates (any form) or riociguat,Hypersensitivity to tadalafil,Concomitant use with alpha-blockers (except for BPH with appropriate dosing)
Pregnancy (category X; risk of hypospadias in male fetuses),Known hypersensitivity to finasteride or any component of the formulation
Avoid high-fat meals prior to dosing as they may delay absorption and reduce peak plasma concentration. Avoid large quantities of grapefruit juice (more than 1 liter per day) as it may increase tadalafil exposure via CYP3A4 inhibition.
No significant food interactions reported; finasteride may be taken with or without food. Avoid excessive alcohol consumption as it may worsen BPH symptoms or liver function.
FDA Pregnancy Category B. Animal studies show no evidence of teratogenicity or embryotoxicity. No adequate, well-controlled studies in pregnant women. Risk cannot be ruled out; use only if clearly needed.
Contraindicated in pregnancy. Finasteride inhibits conversion of testosterone to dihydrotestosterone, which is critical for male fetal external genitalia development. Risk of hypospadias and other urogenital malformations if exposed in utero, particularly during first trimester. Pregnancy category X.
Excretion in human milk unknown. Not recommended for use in nursing mothers. M/P ratio not determined.
Not recommended. Finasteride is excreted in human milk; M/P ratio not reported. Risk to nursing infant unknown, but potential for adverse effects on male infant genitalia. Use contraindicated during breastfeeding.
No specific dose adjustments studied in pregnancy. Use lowest effective dose if necessary, with caution for increased plasma volume and renal clearance potentially altering pharmacokinetics.
No dose adjustments applicable as finasteride is contraindicated in pregnancy. No pharmacokinetic studies in pregnant women due to ethical concerns.
Tadalafil (Cialis) has a 17.5-hour half-life allowing once-daily dosing for ED or daily for BPH/LUTS. Avoid use with nitrates; may cause prolonged erection. Onset of action is 30-60 minutes, and effect may last up to 36 hours. Use with caution in patients with left ventricular outflow obstruction or severe hepatic impairment.
Finasteride inhibits 5α-reductase type II, reducing conversion of testosterone to DHT. Onset of effect in benign prostatic hyperplasia (BPH) requires 6-12 months; for androgenetic alopecia, 3-6 months. Serum PSA levels decrease by approximately 50% after 6 months; multiply PSA by 2 when interpreting. Avoid handling crushed or broken tablets if pregnant or planning to become pregnant due to risk of fetal genital abnormalities. Use with caution in hepatic impairment; contraindicated in women of childbearing potential, children, and patients with hypersensitivity to 5α-reductase inhibitors.
Do not take tadalafil if you take any form of nitrate medication (e.g., nitroglycerin) for chest pain.,Seek immediate medical help if you have an erection lasting more than 4 hours.,Avoid alcohol consumption as it may increase the risk of dizziness and low blood pressure.,Take tadalafil at least 30 minutes before sexual activity; effect can last up to 36 hours.,For daily use, take at the same time each day without regard to timing of sexual activity.,Grapefruit and grapefruit juice may increase tadalafil levels; avoid large amounts.,Inform your doctor of all medications you take, especially alpha-blockers, antihypertensives, and antifungal or antibiotic drugs.
Take finasteride exactly as prescribed, once daily with or without food.,It may take 3-6 months for hair regrowth or improvement in urinary symptoms; continue therapy as directed even if no immediate benefit is noted.,Report any breast tenderness, enlargement, or lumps; also report any new onset of sexual dysfunction (e.g., decreased libido, erectile dysfunction, ejaculation disorder).,Do not donate blood while taking finasteride and for at least 1 month after stopping, to prevent exposure to a pregnant female.,Women who are pregnant or may become pregnant should not handle crushed or broken tablets due to risk of harm to male fetus.,Serum PSA levels will decrease; inform your healthcare provider that you take finasteride before any PSA test.,Store at room temperature (20-25°C) in a dry place, away from light and moisture.
No interactions on record
"Finasteride, a 5α-reductase inhibitor used for benign prostatic hyperplasia, may inhibit cytochrome P450 3A4 (CYP3A4) isoenzymes. Cyclosporine is primarily metabolized by CYP3A4. Coadministration can lead to reduced cyclosporine clearance, elevated blood concentrations, and increased risk of nephrotoxicity, hypertension, and neurotoxicity."
"Finasteride, a 5α-reductase inhibitor used for benign prostatic hyperplasia, may weakly inhibit CYP3A4, the primary enzyme responsible for sildenafil metabolism. This can lead to a modest reduction in sildenafil clearance, increasing systemic exposure and potentially enhancing both therapeutic effects and adverse events such as headache, flushing, dyspepsia, and hypotension. Clinically, this interaction is generally mild but may require dose adjustment in patients predisposed to sildenafil side effects."
"Finasteride, a 5α-reductase inhibitor, may inhibit CYP3A4-mediated metabolism of netupitant, a neurokinin-1 receptor antagonist primarily metabolized by CYP3A4. This can lead to increased netupitant plasma concentrations, potentially enhancing its adverse effects such as headache, fatigue, or dizziness. Clinically, the combination may require dose adjustment or close monitoring for netupitant toxicity."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about CIALIS vs FINASTERIDE, answered by our medical review team.
CIALIS is a PDE5 Inhibitor that works by Phosphodiesterase-5 (PDE5) inhibitor; increases c GMP levels, causing smooth muscle relaxation and vasodilation in the corpus cavernosum, enhancing erectile function.. FINASTERIDE is a 5-alpha Reductase Inhibitor that works by Finasteride is a competitive 5-alpha-reductase inhibitor that prevents conversion of testosterone to dihydrotestosterone (DHT), thereby reducing DHT levels in serum and prostate tissue.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CIALIS and FINASTERIDE depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of CIALIS is: Tadalafil 10 mg or 20 mg orally as needed at least 30 minutes before sexual activity; maximum dosing frequency once daily. Alternative: 2.5 mg or 5 mg once daily for daily use.. The standard adult dose of FINASTERIDE is: 1 mg orally once daily for androgenetic alopecia; 5 mg orally once daily for benign prostatic hyperplasia.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between CIALIS and FINASTERIDE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. CIALIS is classified as Category C. FDA Pregnancy Category B. Animal studies show no evidence of teratogenicity or embryotoxicity. No adequate, well-controlled studies in pregnant women. Risk cannot be ruled out; use. FINASTERIDE is classified as Category D/X. Contraindicated in pregnancy. Finasteride inhibits conversion of testosterone to dihydrotestosterone, which is critical for male fetal external genitalia development. Risk of hypos. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.