Why Cialis Original Lasts 36 Hours When Viagra Lasts 4–6
This is the most common question patients ask — and the pharmacological answer is specific to tadalafil's molecular structure. All three major ED medications (sildenafil/Viagra, tadalafil/Cialis, vardenafil/Levitra) block the PDE-5 enzyme, but they differ dramatically in how long they remain active in the body:
| Parameter | Cialis Original 20mg | Viagra 100mg | Levitra 20mg |
|---|---|---|---|
| Active ingredient | Tadalafil | Sildenafil citrate | Vardenafil |
| Elimination half-life | ~17.5 hours | 3–5 hours | 4–5 hours |
| Duration of action | Up to 36 hours | 4–6 hours | 4–6 hours |
| Onset of action | 30–45 minutes | 30–60 minutes | 15–30 minutes |
| Effect of fatty meals | None — take with or without food | Delays onset by ~60 min | High-fat meals delay onset |
| Available as daily dose | Yes — Cialis 5mg daily | No | No |
| Approved for BPH | Yes | No | No |
| Tadalafil-specific side effect | Back pain, muscle aches (PDE-11 inhibition) | Blue-tinted vision (PDE-6) | None specific beyond class effects |
The practical implication of 36 hours: with Cialis 20mg, you can take a single tablet on Friday evening and remain within the treatment window through Saturday and Sunday — with no need to re-dose, no timing pressure, and no adjusting your evening meal around a pill. For men with spontaneous sexual lifestyles or frequent activity, this represents a fundamentally different experience from Viagra's 4–6 hour on-demand window.
How Tadalafil Works — Mechanism of Action
Tadalafil belongs to the class of selective phosphodiesterase type 5 (PDE-5) inhibitors. The step-by-step mechanism:
- Sexual arousal triggers nitric oxide (NO) release from parasympathetic nerve endings and endothelial cells in the penis
- NO activates guanylate cyclase, which converts GTP to cGMP (cyclic guanosine monophosphate)
- cGMP relaxes smooth muscle cells in the corpora cavernosa, allowing blood to engorge the erectile tissue and produce a firm erection
- Without tadalafil: the PDE-5 enzyme rapidly degrades cGMP — the erection subsides
- With Cialis (tadalafil): PDE-5 is selectively blocked → cGMP remains elevated → enhanced, sustained blood flow → erection maintained throughout sexual activity
Why does tadalafil specifically last 36 hours? Unlike sildenafil and vardenafil, tadalafil has a unique bicyclic ring structure that gives it a much higher affinity for plasma protein binding (94%) and a much slower hepatic metabolism rate — resulting in its 17.5-hour half-life. After a 20mg dose, therapeutic plasma concentrations of tadalafil remain above the minimum effective threshold for approximately 36 hours in most patients. This is purely pharmacokinetic — not a stronger drug, just a longer-lasting one.
Tadalafil and PDE-11: Unlike sildenafil, which inhibits PDE-6 (causing transient blue-tinted vision), tadalafil inhibits PDE-11 — an enzyme found in skeletal muscle and the testes. This is why approximately 6% of men taking Cialis experience back pain or muscle aches, a side effect not seen with Viagra or Levitra. It is benign and resolves within 24–48 hours but is clinically important to know about before your first dose.
Important: Cialis does not produce spontaneous erections. Sexual arousal is essential for the mechanism to engage. Tadalafil amplifies the physiological erectile response — it does not initiate it.
Pharmacokinetics of Cialis Original 20mg
| Parameter | Value | Clinical significance |
|---|---|---|
| Oral bioavailability | ~15% (lower than sildenafil but longer acting) | Compensated by very slow elimination |
| Time to peak plasma (Tmax) | 2 hours (range 30 min – 6 hours) | Onset variable — take 1 hour before for reliability |
| Elimination half-life | 17.5 hours | Responsible for the 36-hour duration — unique to tadalafil |
| Food interaction | None | Take with or without food — no timing adjustment needed |
| Plasma protein binding | 94% | Key factor in slow elimination |
| Metabolism and elimination | Hepatic (CYP3A4), ~61% feces, ~36% urine | Caution with strong CYP3A4 inhibitors (ritonavir, ketoconazole) |
Dosage of Cialis Original — Complete Guide
Cialis Original is available in two distinct treatment approaches, each appropriate for different patient profiles:
| Dose | Approach | For whom | Notes |
|---|---|---|---|
| 10mg | On-demand (as needed) | Starting dose for most men — assess response before increasing | Taken 30–60 min before sexual activity |
| 20mg | On-demand (as needed) | Standard dose when 10mg is insufficient — maximum on-demand dose | Maximum once per 24 hours |
| 5mg | Daily (once every 24h) | Men with frequent sexual activity (≥2×/week) or who prefer continuous readiness; also for BPH | Taken at same time each day, with or without food, regardless of sexual activity |
Dose reduction may be required in: men over 75, severe renal impairment (creatinine clearance <30 mL/min), severe hepatic impairment (Child-Pugh C), and patients taking potent CYP3A4 inhibitors. In these cases, a physician should recommend a lower starting dose of 5mg on-demand.
How to take Cialis Original:
- Swallow the tablet whole with a glass of water
- Take 30–60 minutes before anticipated sexual activity (though it may be taken up to 4 hours before)
- Food does not affect absorption — take with or without a meal, unlike Viagra or Levitra
- Do not exceed 20mg in any 24-hour period
- Do not take grapefruit juice — inhibits CYP3A4 and raises tadalafil plasma levels unpredictably
Cialis for Benign Prostatic Hyperplasia (BPH) — A Unique Dual Indication
Cialis (tadalafil 5mg daily) is the only PDE-5 inhibitor approved by Health Canada for both erectile dysfunction and benign prostatic hyperplasia (enlarged prostate). This dual indication makes it particularly valuable for older men who commonly experience both conditions simultaneously.
How tadalafil treats BPH: the prostate and bladder smooth muscle contain PDE-5. Tadalafil relaxes this smooth muscle, reducing urinary resistance and improving urinary flow. Clinical trials demonstrated significant improvements in International Prostate Symptom Score (IPSS) with daily tadalafil 5mg.
Symptoms of BPH improved by Cialis 5mg daily:
- Weak or intermittent urinary stream
- Difficulty starting urination
- Frequent urination, especially at night (nocturia)
- Feeling of incomplete bladder emptying
- Urgency to urinate
For men with both ED and BPH, daily Cialis 5mg addresses both conditions with a single daily tablet — a clinically and practically significant advantage over alpha-blockers plus on-demand ED medication.
Side Effects of Cialis Original
The back pain associated with Cialis is predictable and manageable: it typically appears 12–24 hours after taking a 20mg dose (not immediately), and resolves within 24–48 hours without treatment. It is caused by tadalafil's inhibition of PDE-11 in skeletal muscle — not a sign of injury. Over-the-counter analgesics (acetaminophen, ibuprofen) are generally effective if it causes discomfort. Men who find it bothersome may prefer switching to 10mg on-demand or daily 5mg, where the back pain incidence is lower.
Why Cialis does not cause blue-tinted vision (unlike Viagra): Viagra causes transient visual colour disturbance because sildenafil inhibits PDE-6 in retinal photoreceptors. Tadalafil has far lower affinity for PDE-6 — this side effect is not clinically associated with Cialis. If you experience sudden or complete vision loss while taking Cialis, stop immediately and seek emergency care — this may indicate NAION (non-arteritic anterior ischaemic optic neuropathy), a rare but serious event.
Contraindications — Who Should Not Take Cialis
Absolute contraindications — do not take Cialis if you:
- Take any nitrate medications — nitroglycerin, isosorbide mononitrate, isosorbide dinitrate (prescribed for angina or heart disease). The combination with any PDE-5 inhibitor causes potentially fatal hypotension. This is an absolute, non-negotiable contraindication
- Use poppers (amyl nitrite or butyl nitrite) — same lethal interaction mechanism as prescription nitrates
- Take riociguat (Adempas) for pulmonary arterial hypertension
- Have had a myocardial infarction or stroke within the last 90 days
- Have unstable angina or angina occurring during sexual intercourse
- Have severe heart failure (NYHA Class II or worse) with recent hospitalisation
- Have severe uncontrolled hypertension (>170/100 mmHg) or severely low blood pressure (<90/50 mmHg)
- Have lost vision in one eye due to previous NAION
- Are allergic to tadalafil or any excipient in the Cialis tablet
Use with caution — consult your doctor if you:
- Take alpha-blockers (tamsulosin, doxazosin, alfuzosin) for BPH or hypertension — risk of symptomatic hypotension. A minimum 4-hour separation between the alpha-blocker and tadalafil is recommended, except for tamsulosin 0.4mg which may be combined with tadalafil
- Take potent CYP3A4 inhibitors (ritonavir, ketoconazole, itraconazole, clarithromycin) — these significantly increase plasma tadalafil levels. Maximum dose should be reduced to 10mg on-demand or 2.5mg daily
- Have severe renal impairment (creatinine clearance <30 mL/min) — dose capped at 5mg daily or 10mg on-demand every 48 hours
- Have severe hepatic impairment (Child-Pugh C) — tadalafil not recommended; if used, dose capped at 10mg
- Have anatomical deformation of the penis (Peyronie's disease) or conditions predisposing to priapism (sickle cell anaemia, multiple myeloma, leukaemia)
- Are over 75 — slower tadalafil clearance; physician should evaluate starting dose
- Are diabetic — ED and cardiovascular risk frequently coexist; cardiological assessment recommended before starting
Drug Interactions
| Drug / Substance | Interaction | Recommendation |
|---|---|---|
| Nitrates (nitroglycerin, isosorbide) | Severe, potentially fatal hypotension | Absolutely contraindicated |
| Poppers (amyl/butyl nitrite) | Same mechanism as nitrates — dangerous BP drop | Absolutely contraindicated |
| Alpha-blockers (tamsulosin, doxazosin) | Additive hypotension — particularly relevant for BPH patients | Minimum 4h gap; tamsulosin 0.4mg may be combined |
| CYP3A4 inhibitors (ritonavir, ketoconazole) | Significantly increases tadalafil plasma levels | Reduce max dose to 10mg on-demand every 72h |
| Other PDE-5 inhibitors (Viagra, Levitra) | Additive hypotension — never combine | Wait ≥36–48h after Cialis before taking another |
| Alcohol | Additive blood pressure lowering — more pronounced than with sildenafil | Maximum 1–2 standard drinks; avoid heavy drinking |
| Grapefruit / grapefruit juice | Inhibits CYP3A4 → unpredictable tadalafil level increases | Avoid completely while using Cialis |
Delivery to All Canadian Provinces and Territories
We ship Cialis Original 20mg with complete discretion to all provinces and territories across Canada in 4–9 business days. Every order is dispatched in plain, unmarked packaging with no indication of contents on the outside — your privacy is fully protected at every stage.
Ontario (Toronto, Ottawa, Mississauga, Brampton, Hamilton, London, Windsor) — Quebec (Montreal, Quebec City, Laval, Gatineau, Longueuil) — British Columbia (Vancouver, Surrey, Burnaby, Richmond, Kelowna, Victoria) — Alberta (Calgary, Edmonton, Red Deer, Lethbridge) — Manitoba (Winnipeg, Brandon) — Saskatchewan (Saskatoon, Regina) — Nova Scotia (Halifax, Dartmouth) — New Brunswick (Fredericton, Moncton, Saint John) — Newfoundland and Labrador (St. John's) — Prince Edward Island (Charlottetown) — Northwest Territories, Yukon, Nunavut — and all other cities and communities across Canada.
Frequently Asked Questions — Cialis Original Canada
How is Cialis Original different from generic tadalafil? Cialis Original contains tadalafil manufactured by Eli Lilly under their brand formulation, quality control and packaging. Generic tadalafil contains the same active ingredient at the same dose, manufactured by licensed generic pharmaceutical companies. Both are pharmacologically equivalent — same molecule, same dose, same bioavailability. The differences are manufacturer, brand recognition and price. Generic tadalafil is significantly less expensive; Cialis Original offers the assurance of Eli Lilly's manufacturing standards.
Can I buy Cialis without a prescription in Canada? Tadalafil is a Schedule F prescription medication in Canada when purchased from a licensed Canadian pharmacy. Drugs-Canada.com is an international online pharmacy operating in the grey market of personal importation. If you would like a legitimate Canadian prescription for tadalafil, telehealth services such as Maple, Tia Health or Felix offer physician consultations and electronic prescriptions within hours.
Does Cialis really work for 36 hours? Yes — this is pharmacologically established, not marketing. Tadalafil's 17.5-hour half-life means that after a 20mg dose, plasma concentrations remain above the minimum effective threshold for approximately 36 hours in most patients. Clinical trials published in the Journal of Urology and Urology confirmed the 36-hour window with statistically significant erectile function improvements compared to placebo throughout that period. Individual results vary based on age, kidney and liver function.
I have BPH as well as ED — is Cialis the right choice for me? Possibly, yes. Cialis (tadalafil 5mg daily) is the only ED medication clinically approved for both conditions simultaneously. Clinical trials showed significant improvements in International Prostate Symptom Score (IPSS) alongside erectile function improvements with daily tadalafil. Discuss with your urologist whether the combination indication applies to your specific case.
Why does Cialis cause back pain when Viagra doesn't? Tadalafil inhibits PDE-11 — an enzyme found in skeletal muscle — in addition to PDE-5. This causes mild myalgia (muscle aches) and back pain in approximately 6% of patients, typically appearing 12–24 hours after the dose. Sildenafil has much lower affinity for PDE-11, which is why this side effect is not associated with Viagra. The back pain is benign, resolves within 48 hours, and can be managed with OTC analgesics. If it is persistently bothersome, switching to 10mg doses or daily 5mg often reduces or eliminates it.
How long should I wait after taking Cialis before I can take Viagra or Levitra? Due to Cialis's 17.5-hour half-life, you should wait a minimum of 36–48 hours after a 20mg Cialis dose before taking any other PDE-5 inhibitor. Taking them closer together risks additive hypotension. Never take two ED medications simultaneously.
Is Cialis safe for older men (over 65)? Yes, with appropriate dose management. Tadalafil clearance decreases with age — men over 75 may have plasma levels up to 25% higher than younger men at the same dose. Starting with 10mg on-demand (rather than 20mg) is often recommended for men over 65. Over 75, physician evaluation before starting is advisable. Older men are also more likely to take alpha-blockers for BPH — ensure appropriate timing separation.
Can I take Cialis daily instead of on-demand? Yes — daily Cialis 5mg is a Health Canada-approved regimen for both ED and BPH. It provides a steady-state tadalafil blood level allowing spontaneous sexual activity without timing a dose. Clinical data shows comparable efficacy to on-demand 20mg for ED, with the additional benefit of eliminating the pre-sex planning requirement entirely. Daily dosing is generally preferred by men with frequent sexual activity (more than twice weekly) or those who value full spontaneity.
How quickly does Cialis take effect compared to Viagra? The onset of Cialis is typically 30–45 minutes, slightly faster than Viagra's 30–60 minutes on average. However, Cialis' Tmax (time to peak plasma concentration) is approximately 2 hours — later than sildenafil's 60 minutes — meaning peak effect may arrive later. The practical advantage is that Cialis can be taken up to 4 hours before sexual activity with maintained efficacy, offering significantly more flexibility than Viagra.
The information on this page is for educational purposes only and does not constitute medical advice. Tadalafil (Cialis) is a prescription medication requiring prior medical assessment, particularly in patients with cardiovascular disease or those taking other medications. Always consult a licensed healthcare provider before starting treatment. If you experience an erection lasting more than 4 hours, sudden vision or hearing loss, or chest pain during sexual activity, seek emergency medical care immediately — call 911.
