Cialis — the brand name for tadalafil — is the other widely used PDE5 inhibitor in the UK, alongside sildenafil. Patients often ask how it compares on timing, and the honest answer is that the pharmacology is meaningfully different. Tadalafil reaches peak levels at roughly the same point as sildenafil, but its half-life is much longer, which is what gives it the "weekend pill" reputation. This piece walks through what that actually means in practice — onset, peak, duration, the on-demand versus daily dosing decision, and the safety points your prescriber will go through before treatment.
Tadalafil's pharmacokinetics — in plain English
After a tablet is swallowed, tadalafil is absorbed from the gut and starts to appear in the bloodstream relatively quickly. The medicine reaches its peak plasma concentration around two hours after the dose. The onset of effect — the point at which the medicine is already in the system in useful amounts — is usually a little earlier than that, often within 30 to 60 minutes for many men, particularly with regular use.
The standout feature of tadalafil is what happens after the peak. Its half-life is around 17.5 hours, much longer than the four-to-five-hour half-life of sildenafil. A half-life is the time it takes for plasma levels to fall by half, so even after a single dose, useful amounts of the medicine remain in circulation for a long stretch. Functionally, this means the active window — when tadalafil can amplify the body's natural erectile signal during sexual arousal — extends for up to 36 hours after the tablet.
Like all PDE5 inhibitors, tadalafil itself does not produce an erection. It blocks PDE5, the enzyme that breaks down cGMP — the second messenger released during sexual arousal that relaxes the smooth muscle in the small arteries of the penis. The mechanism is the same one that Viagra and other PDE5 inhibitors use. Sexual stimulation is still required for that pathway to be activated. Without arousal, the tablet simply sits in the system, doing nothing visible.
On-demand versus daily dosing — different timelines
In the UK, tadalafil is licensed for two distinct dosing strategies, and they have different timelines worth understanding.
On-demand tadalafil is taken at 10 mg or 20 mg before anticipated sexual activity, usually at least 30 minutes ahead. The patient is using the up-to-36-hour active window, picking a single dose to cover a longer time frame. This is the regimen most people picture when they think of Cialis.
Daily tadalafil 5 mg is a different regimen entirely. The tablet is taken at the same time every day, regardless of whether sexual activity is planned. After about five days of consistent dosing, plasma levels reach a steady state — meaning the medicine sits at a stable, low level in the system continuously. The pharmacology of an erection then runs against that steady background, without the user needing to plan a dose around any particular occasion.
The daily regimen also has a separate licensed use: benign prostatic enlargement (BPE), where it can improve lower-urinary-tract symptoms in some men. For a patient who has both erectile dysfunction and BPE, daily tadalafil is sometimes the more useful choice. Your clinician will advise based on your individual circumstances — frequency of sexual activity, lifestyle pattern, other conditions, and any interacting medications.
Why food affects timing less than with sildenafil
Sildenafil absorption can be slowed by a heavy meal — particularly one high in fat — pushing the onset back by 30 to 60 minutes. Tadalafil is far less sensitive to this. Studies in the licensing programme found no clinically meaningful effect of food on either the peak plasma level or the total exposure to the drug. From a patient's perspective, that means a tadalafil tablet taken with dinner is not significantly different from one taken on an empty stomach.
This is a real practical advantage for men who would otherwise need to plan a dose around food. The same is not true of alcohol. Although tadalafil's absorption is not affected by alcohol pharmacokinetically, heavier alcohol intake blunts arousal and impairs the erectile response independently of medicine. The result of taking tadalafil after several drinks is often disappointing, and that is a behavioural rather than pharmacological issue.
For more on the underlying biology of why arousal is essential, our piece on how Viagra works covers the same nitric-oxide pathway in more detail.
What "lasts 36 hours" really means
The "36 hours" figure is one of the most commonly quoted facts about Cialis, and it is also one of the most commonly misunderstood. It does not mean a continuous 36-hour erection. It does not mean a sustained sexual response. It means that for up to 36 hours after the dose, enough tadalafil remains in the system to amplify the natural cGMP signal whenever sexual arousal occurs in that window.
For some men, that long window is the most useful feature of the medicine — it removes the need to time a tablet to a specific moment, which can take pressure off the situation. For others, particularly those who want sexual activity once and then stop thinking about it, sildenafil's shorter four-to-five-hour window is a better fit. Neither is "better" in the abstract; the right choice is the one that fits the man's life, the partner's preferences and the medical picture.
It is also worth noting that the active window does not mean side effects last the same length of time. Most common side effects of tadalafil — headache, indigestion, muscle aches, back pain, flushing and nasal congestion — appear within the first few hours and largely settle long before the medicine is cleared. Persistent side effects should always be reviewed.
Adjusting timing with clinical advice
The right dose and the right regimen of tadalafil are not the same for every man, and either can be adjusted after seeing how the first prescription performs. A clinician will typically start with on-demand 10 mg for a patient new to PDE5 inhibitors, and adjust up to 20 mg or across to the 5 mg daily regimen depending on response and tolerability. Patients on certain other medications — alpha-blockers for the prostate or for blood pressure, some antifungals, some HIV treatments — need a lower starting dose or careful monitoring, because plasma levels of tadalafil can climb higher than expected.
Repeat use, side-effect patterns and any changes in cardiovascular health all feed into the dose conversation at review. Tadalafil is reviewed periodically rather than prescribed and forgotten. For patients also considering the OTC pathway for sildenafil, our piece on buying Viagra over the counter in the UK explains the pharmacy-only Viagra Connect route and how it differs from a prescription consultation. The Men's Health hub on the blog collects related topics.
How a Farmeci consultation works
An online consultation with a Farmeci-registered prescriber for tadalafil follows the same regulatory standards as a high-street pharmacy. The clinician reviews your medical history, current medications and lifestyle factors, and discusses whether on-demand or daily tadalafil — or a different PDE5 inhibitor — is the better fit. If treatment is appropriate, it is dispensed by our GPhC-registered pharmacy. If not, the clinician will explain why and outline the next sensible step, which may be further investigation rather than a prescription.