How does Cialis work? A complete guide for UK patients
- What Cialis is and how it works at a biological level
- How long Cialis takes to work and how long it lasts
- How Cialis compares to Viagra on efficacy, duration, and side effects
- How to get the maximum effect from Cialis
- Who should not take Cialis and how to access it in the UK
- What is Cialis?
- How does Cialis work?
- How long does Cialis take to work?
- How long does Cialis last?
- Cialis 5mg daily: How long before it works consistently?
- Is Cialis better than Viagra?
- Is 20mg Cialis equal to 100mg Viagra?
- How to get maximum effect from Cialis
- Does Cialis lower blood pressure?
- What are the benefits of Cialis?
- Who should not take Cialis?
- How to get Cialis in the UK
- Final thoughts
What is Cialis?
Cialis is the brand name for generic tadalafil, a prescription medicine manufactured by Eli Lilly and licensed by the MHRA for erectile dysfunction and benign prostatic hyperplasia (BPH). It belongs to a class of medicines called PDE5 inhibitors, which also includes sildenafil (Viagra) and vardenafil (Levitra).
Cialis is available in four doses: 2.5 mg and 5 mg for daily use, and 10 mg and 20 mg for on-demand use. Generic tadalafil, containing the same active ingredient at the same doses, is also widely available at lower cost. For full details on available doses, see our Cialis dosage guide.
How does Cialis work?
Cialis works by inhibiting PDE5, an enzyme that limits blood flow to the penis. By blocking this enzyme, it allows the blood vessels in the penis to relax and fill, producing an erection in the presence of sexual stimulation.
When a man is sexually aroused, the body releases nitric oxide in the penile tissue, triggering production of cyclic GMP (cGMP), a chemical messenger that relaxes smooth muscle in the penile arteries and allows blood to flow in. PDE5 breaks down cGMP, ending the erection. Cialis inhibits PDE5, allowing cGMP to remain active for longer and making it easier to achieve and maintain an erection during arousal.
Cialis does not produce an erection independently. Sexual stimulation is always required.
Good to know
Tadalafil also partially inhibits PDE11, an enzyme in skeletal muscle tissue. This is thought to explain why back pain and muscle aches are more commonly reported with Cialis than with sildenafil.
How long does Cialis take to work?
Cialis typically takes effect within 30-60 minutes of taking a dose. Unlike Viagra, it is not significantly affected by food and can be taken with or without a meal. Some prescribers advise taking it up to two hours before anticipated activity to allow for fuller absorption if 30 minutes proves insufficient.
How long does Cialis last?
Cialis remains active for up to 36 hours after a single on-demand dose, significantly longer than Viagra's 4-6 hours. This extended duration is why Cialis is often called "the weekend pill." A single dose taken on a Friday evening can remain effective through the weekend without a further dose.
For men taking 5 mg daily, a continuous therapeutic level is maintained, removing the need to time doses around sexual activity altogether.
Cialis 5mg daily: How long before it works consistently?
The full effect of daily 5 mg Cialis is typically established within 5-7 days of consistent dosing, once stable blood levels are reached. Treatment usually begins at 2.5 mg for two weeks to assess tolerability before increasing to 5 mg if needed.
Is Cialis better than Viagra?
Neither is clinically superior. Both produce comparable rates of successful erections in clinical trials. The choice depends on lifestyle and individual tolerability.
| Cialis (tadalafil) | Viagra (sildenafil) | |
|---|---|---|
| Onset | 30–60 minutes | 30–60 minutes |
| Duration | Up to 36 hours | 4–6 hours |
| Food interaction | Minimal | Avoid high-fat meals |
| Daily use option | Yes (2.5 mg, 5 mg) | No |
| Back pain and muscle aches | More common | Not typically reported |
| Visual disturbances | Less common | More common |
Cialis suits men who value spontaneity or have sex frequently. Viagra suits men who prefer a shorter treatment window or are primarily motivated by cost.
Is 20mg Cialis equal to 100mg Viagra?
No. A direct milligram comparison is not clinically meaningful. Tadalafil and sildenafil have different molecular structures and dose-response curves. Both produce comparable outcomes at their respective recommended doses, reflecting differences in molecular potency rather than strength. If switching between the two, your prescriber will determine the appropriate starting dose.
How to get maximum effect from Cialis
- Allow sufficient time: Take on-demand Cialis at least 30 minutes before sexual activity
- Sexual stimulation is required: Cialis does not work without arousal
- Moderate alcohol: Alcohol compounds Cialis's blood pressure-lowering effect and worsens side effects. Keep intake moderate
- Avoid nitrate-containing recreational drugs: Amyl nitrite (poppers) is absolutely contraindicated with Cialis
- Be consistent with daily dosing: Take 5 mg daily at the same time each day for the most stable blood levels
Does Cialis lower blood pressure?
Yes, modestly. For most healthy men this is not significant, but it can be more pronounced in men taking antihypertensives or alpha-blockers. The most serious concern is the absolute contraindication with nitrates: combining tadalafil and nitrates can produce a severe and potentially life-threatening drop in blood pressure.
Warning!
Never take Cialis if you are taking any form of nitrate medication, including glyceryl trinitrate for chest pain or amyl nitrite (poppers). Always disclose all current medications to your prescriber before starting. For a full safety overview, see our Cialis side effects guide.
What are the benefits of Cialis?
- Up to 36 hours of efficacy from a single on-demand dose
- Daily dosing option removes the need to time doses around sexual activity
- Minimal food interaction compared to Viagra
- Licensed for both ED and BPH
- Well-studied safety profile with over two decades of clinical data
Who should not take Cialis?
Cialis must not be used by men who take nitrate medications in any form, have been advised to avoid sexual activity due to cardiovascular risk, have had a recent stroke or heart attack, have severe liver impairment, have low or uncontrolled blood pressure, or have a known hypersensitivity to tadalafil.
How to get Cialis in the UK
Cialis is prescription-only and requires a clinical assessment by a UK-registered prescriber. Legitimate routes include a GP (NHS or private) or a regulated online clinic. DoktorABC connects UK patients with licensed prescribers who can assess suitability and issue private prescriptions where clinically appropriate. For a full overview of purchasing options, see our guide to where to buy Cialis.
Final thoughts
Cialis is a well-evidenced treatment for ED with a longer duration than most alternatives. The choice between Cialis and other ED treatment options comes down to individual lifestyle, tolerability, and cost rather than one being objectively superior. A clinical assessment before starting is essential, and all dosing decisions should be made with a registered prescriber.
DoktorABC connects UK patients with licensed prescribers who can assess suitability for Cialis and issue private prescriptions where clinically appropriate.
FAQ
What is Cialis?
The brand name for tadalafil, a PDE5 inhibitor licensed for ED and BPH in the UK.
How does Cialis work?
By inhibiting PDE5, allowing cGMP to accumulate in penile blood vessels, which relaxes smooth muscle and increases blood flow in the presence of sexual stimulation.
How long does Cialis last?
Up to 36 hours from a single on-demand dose. Daily 5 mg Cialis maintains a continuous therapeutic level.
How long does Cialis take to work?
Typically 30 to 60 minutes. It is not significantly affected by food.
Is Cialis better than Viagra?
Neither is clinically superior. Cialis offers a longer duration and daily dose option; Viagra offers a shorter window and lower cost via generic sildenafil.
Is 20mg Cialis equal to 100mg Viagra?
No. A direct milligram comparison is not meaningful. Both produce comparable outcomes at their respective recommended doses.
How long before Cialis 5mg daily works consistently?
Typically five to seven days of consistent daily dosing.
Does Cialis lower blood pressure?
Yes, modestly. It must never be taken with nitrates.
How do I get Cialis in the UK?
Via a GP prescription or a regulated online clinic. Always verify GPhC and CQC registration before using any online service.
The DoktorABC medical advisory board
Dr. Roland Ruiken
Medical advisor, Norway
Dr. Viktor Simunovic
Medical advisor, Croatia