Tadalafil (Cialis)
Is It Right for You?
A complete guide to Tadalafil (Cialis) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Tadalafil (Cialis)?
Tadalafil, sold under the brand name Cialis and widely available as generic tadalafil, is a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction (ED), the symptoms of benign prostatic hyperplasia (BPH), and pulmonary arterial hypertension (under specialist supervision). It is one of the most widely prescribed and recognised medications for erectile dysfunction in the world.
Tadalafil is distinguished from other PDE5 inhibitors — such as sildenafil (Viagra) — primarily by its exceptionally long duration of action: up to 36 hours, earning it the informal nickname "the weekend pill." This pharmacokinetic advantage allows for greater spontaneity compared to shorter-acting alternatives, as it does not need to be taken close in time to sexual activity. Additionally, tadalafil is available in a once-daily low-dose formulation (2.5 mg or 5 mg) that provides continuous background coverage for men who prefer not to plan their medication around sexual activity or who also have BPH symptoms.
Tadalafil was approved by the European Medicines Agency and has been in widespread clinical use since the early 2000s. It has an extensive evidence base supporting its efficacy and safety in men across a broad range of age groups, cardiovascular risk profiles (with appropriate assessment), and underlying causes of erectile dysfunction.
Tadalafil is available both on prescription and — for the 10 mg dose — over the counter from UK pharmacies for men aged 18–64 after a pharmacist consultation. The 2.5 mg, 5 mg, and 20 mg doses remain prescription-only.
What Conditions Is Tadalafil Used For?
Tadalafil is indicated for:
inability to achieve or maintain an erection sufficient for satisfactory sexual performance; tadalafil is effective across all severity grades and underlying causes, including psychogenic, vasculogenic, and mixed aetiology.
tadalafil 5 mg once daily is licensed for the treatment of lower urinary tract symptoms (LUTS) associated with BPH, including urinary urgency, frequency, weak stream, and incomplete bladder emptying.
tadalafil 5 mg once daily effectively treats both conditions simultaneously, making it a convenient option for men experiencing both.
Tadalafil enhances the physiological erectile response to sexual stimulation but does not cause automatic erections. Sexual arousal is necessary for the medication to be effective.
How Does Tadalafil Work?
Tadalafil works by inhibiting phosphodiesterase type 5 (PDE5), an enzyme that degrades cyclic guanosine monophosphate (cGMP) in the smooth muscle cells of the penile arteries and corpus cavernosum.
The normal erectile mechanism proceeds as follows: sexual stimulation triggers the release of nitric oxide (NO) from nerve endings and endothelial cells in the penis. Nitric oxide activates guanylate cyclase, which increases levels of cGMP. Elevated cGMP causes smooth muscle relaxation in the penile arteries and sinusoids of the corpus cavernosum, allowing blood to flow in and the erectile tissue to expand and fill, producing an erection. PDE5 normally degrades cGMP, terminating the erection.
By inhibiting PDE5, tadalafil prevents cGMP breakdown, sustaining and potentiating the vasodilatory and erectile response to sexual stimulation. This requires baseline nitric oxide activity triggered by sexual arousal — it does not produce erections independently.
The same mechanism explains tadalafil's effect in BPH and LUTS — PDE5 is expressed in the smooth muscle of the prostate, bladder neck, and urethra, and its inhibition reduces muscle tone in these structures, improving urinary flow and reducing obstructive and irritative urinary symptoms.
Tadalafil's long duration of action (half-life approximately 17.5 hours; duration of effect up to 36 hours) distinguishes it from sildenafil and vardenafil, which have shorter half-lives of approximately 4–5 hours.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Tadalafil can be taken with or without food. Unlike sildenafil, a high-fat meal does not significantly delay absorption.
For as-needed use, take at least 30 minutes before anticipated sexual activity. Due to the long duration of action, the effect can last up to 36 hours — though sexual stimulation remains necessary throughout this period.
For once-daily dosing, take at the same time each day. There is no need to time the dose relative to sexual activity, and steady-state plasma levels are reached after approximately 5 days.
Do not take more than one dose in 24 hours for as-needed formulations.
Avoid drinking large quantities of alcohol before sexual activity when taking tadalafil — both lower blood pressure and the combination increases the risk of dizziness, light-headedness, and fainting.
Side Effects of Tadalafil
Tadalafil is generally well tolerated, with most side effects being mild and transient.
- Headache
- Flushing
- Indigestion
- Back pain
- Dizziness
- Severe hypotension — particularly dangerous if nitrates are taken concurrently.
- Priapism — painful erection lasting more than 4 hours; requires urgent care.
Tadalafil is contraindicated in patients taking nitrates due to the risk of severe hypotension. Always disclose all medications to your clinician.
Drug Interactions
Tadalafil may interact with other medications, including nitrates and alpha-blockers. Always inform your clinician about all medications you are taking.
Profound, potentially fatal hypotension. Never combine. This includes GTN spray, long-acting nitrates, and amyl nitrite ("poppers").
Significant additive hypotension, particularly on standing. If concurrent use is necessary (e.g. tamsulosin and tadalafil for BPH), initiate at the lowest tadalafil dose and titrate with care.
Contraindicated; combined use causes significant hypotension.
May significantly increase tadalafil plasma concentrations, enhancing side effects. Dose reduction may be required.
Important Warnings
Taking tadalafil with nitrates of any form (including GTN spray, nitrate patches, oral nitrates, or amyl nitrite/poppers) is absolutely contraindicated. The combination causes a severe, potentially fatal drop in blood pressure. If you take any form of nitrate, you must not use tadalafil. Always disclose all cardiac medications to your clinician before being prescribed tadalafil.
An erection lasting more than 4 hours (priapism) is a medical emergency. Without prompt treatment, permanent damage to the erectile tissue can cause irreversible erectile dysfunction. If an erection persists beyond 4 hours, go to an emergency department immediately.
Sexual activity places cardiovascular demands on the heart. Patients with significant cardiovascular disease (recent MI, unstable angina, severe heart failure, uncontrolled arrhythmias, or a resting BP below 90/50 or above 170/100) should be assessed by a clinician before tadalafil is prescribed. The safety of sexual activity itself — and of tadalafil — must be established.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Tadalafil FAQs
Yes. A licensed clinician can assess your suitability via a telehealth consultation, including screening for cardiovascular risk and confirming the absence of nitrate use or other contraindications. Prescriptions for 2.5 mg, 5 mg, and 20 mg doses are prescription-only and require a clinical assessment.
Tadalafil can remain active for up to 36 hours after a single dose. This does not mean a continuous erection — it means the ability to achieve an erection in response to sexual stimulation is enhanced for this duration.
The as-needed dose (10–20 mg) is taken approximately 30 minutes before anticipated sexual activity and is suitable for men who have planned sexual encounters. The once-daily dose (2.5–5 mg) maintains a steady background level of tadalafil in the body, allowing sexual activity at any time without planning, and is also effective for BPH symptoms.
Neither is objectively "better" — they are different with different characteristics. Tadalafil lasts much longer (36 hours vs 4–6 hours), is less affected by food, and offers a daily low-dose option. Sildenafil may act slightly faster. The best choice depends on lifestyle, frequency of sexual activity, and individual response. Both are similarly effective in clinical trials.
If tadalafil is ineffective, first ensure it has been tried on at least 4–8 occasions with adequate sexual stimulation. Response may improve with continued use. The dose may be increased (e.g. from 10 mg to 20 mg). If there is still no response, discuss alternative treatments with your clinician — including further investigation of underlying causes of ED.
Yes. Tadalafil 5 mg once daily is licensed for the treatment of lower urinary tract symptoms caused by benign prostatic hyperplasia, including poor urine flow, urgency, and frequency. It is particularly useful in men who have both ED and BPH, as a single daily tablet addresses both conditions.