Cialis tablets are a widely prescribed treatment for erectile dysfunction (ED). If you're looking to buy Cialis online, start with our short online consultation. You can buy Cialis once our UK-registered clinical team has personally reviewed your answers.
What is Cialis?
Cialis is a treatment for ED. It can help you get and keep an erection when you're sexually stimulated. It belongs to a group of medicines called phosphodiesterase-5 (PDE5) inhibitors and is available in 4 doses: 2.5mg, 5mg, 10mg and 20mg.
Cialis Tadalafil 2.5mg and 5mg are approved for daily use to treat ED. The 10mg and 20mg doses are generally taken when needed, before sexual activity. A consultation with a doctor is recommended to find a suitable dose for you.
How does Cialis work?
To understand how Cialis treats erectile dysfunction, it helps to first understand how erections work. When you're sexually aroused (for example through touch, thoughts or scents), your body releases nitric oxide. This increases a chemical called cyclic guanosine monophosphate (cGMP), which relaxes the corpora cavernosa muscles on the sides of the penis, allowing blood to flow into the penis.
At the same time, the veins that drain blood from the penis narrow. This traps more blood in the penis, which leads to an erection. An enzyme called PDE5 breaks down cGMP, which makes the penis go soft again. PDE5 inhibitors, such as Cialis or Viagra, block this enzyme. This keeps cGMP levels higher, making it easier to get and keep an erection.
You still need sexual stimulation for Cialis to work. It doesn't cause an erection on its own.
Who is Cialis suitable for?
Cialis may be suitable for adult men, or people assigned male at birth, who have erectile dysfunction and are medically suitable for Tadalafil. It may be an option if you'd like a longer-acting ED treatment that you can take before planned sexual activity.
Cialis isn't suitable for everyone, including people who take nitrate medicines. Your prescriber will review your health, your current medicines and your consultation answers. They'll check whether Cialis, and the dose you've chosen, are right for you.
Cialis directions
Cialis should be taken at least 30 minutes before sexual activity. Cialis is a long-acting medicine. It can stay active in your body for up to 36 hours.
Some people find it works better when they take it at least 2 hours before sex. Food doesn't affect how Cialis is absorbed, so you can take it with or without food.
Start your consultation
Once you've started your consultation, a UK-registered prescriber reviews your answers individually to check whether Cialis is right for you. If it's approved, your prescription is dispensed by our pharmacy, which is regulated by the General Pharmaceutical Council (GPhC). We send it out in discreet, unbranded packaging, and our UK-based clinical team is on hand, free of charge, if you have any questions along the way.
Side effects of Cialis
Common side effects of Cialis include:
Back pain
Muscle aches
Pain in the arms and legs
Facial flushing
Blocked or stuffy nose (nasal congestion)
Indigestion
Headache
If any of these side effects last or get worse, see a doctor.
In rare cases, Cialis can cause serious side effects. These include:
A sudden drop in hearing, which may come with tinnitus (ringing in the ears), dizziness or both
Sudden loss of vision in one or both eyes. One example is non-arteritic anterior ischaemic optic neuropathy (NAION), an eye condition that causes sudden vision loss
An erection that lasts much longer than normal (priapism), possibly for several hours
If you experience hearing or vision loss, or if your erection lasts for 4 hours or more, stop taking Cialis and get medical help straight away.
Cialis warnings
Don't take Cialis if you:
Take nitrate medicines, which are used to treat angina (chest pain)
Are allergic to Cialis or any of its ingredients
Take guanylate cyclase stimulators, such as Riociguat (Adempas)
Have had a heart attack within the last 90 days
Have had a stroke within the last 6 months
Have uncontrolled high blood pressure or low blood pressure
Have previously lost vision because of NAION
To check Cialis is suitable for you, share your full medical history with the doctor. This includes telling them if you:
Have had a heart attack, or have an irregular heartbeat, angina, chest pain, aortic valve narrowing or heart failure
Have pulmonary hypertension (high blood pressure in the lungs)
Have had an erection that lasted longer than 4 hours
Have uncontrolled high or low blood pressure
Have liver problems
Have a blood cell disorder, such as sickle cell anaemia, multiple myeloma or leukaemia
Have a deformity of the penis
Have recently had a stroke
Have stomach or intestinal ulcers
Have any other medical condition
Also tell your doctor about all the medicines you take. This includes prescription and over-the-counter medicines, vitamins and herbal supplements.
Cialis may affect how other medicines work and may cause unwanted effects.
How long does Cialis take to begin working?
Depending on your dose and how it's prescribed, Cialis can take between 30 minutes and 2 hours to start working. The effects of Cialis can last for up to 36 hours.
Is Cialis safe to use for erectile dysfunction?
Cialis is an established treatment for erectile dysfunction. Like all medicines, it can cause side effects and isn't suitable for everyone. Your prescriber will check whether it's right for you, based on your health and any other medicines you take.
What dosage of Cialis should you take?
Your doctor will help you find the right dose. This depends on whether you've taken Cialis before and, if so, how well that dose worked for you.
How often should Cialis be taken to combat erectile dysfunction?
Only take Cialis once in a 24-hour period. Cialis can stay active in your body for up to 36 hours.
What is a standard dose of Cialis?
If your doctor prescribes Cialis to take when needed for ED, the usual starting dose is 10mg before sexual activity. If 10mg of Cialis doesn't work well enough, your doctor may increase the dose to 20mg.
The maximum dose of Cialis is 20mg a day.
Is it possible for Cialis to cause stomach pain?
Yes, Cialis can cause stomach ache in some people. You can find more information in the patient information leaflet that comes with your Cialis.
Is it safe to use Cialis with other medications?
Talk to your doctor to check whether any of your other medicines could interact with Cialis. They'll also consider your medical history, including any treatments you've had before.
Is there a generic, lower-cost version of Tadalafil/Cialis?
Yes. Tadalafil, the generic version of the medicine, is now available. It contains the same active ingredient as Cialis, so it should work in a similar way. Tadalafil can be made by companies other than Lilly (the company that makes Cialis).
What if the Cialis dose purchased is ineffective in treating erectile dysfunction?
If your prescribed dose isn't working, talk to your doctor. They may suggest a different dose or another treatment.
Is it okay to eat or drink alcohol whilst using Cialis?
Food doesn't usually change how well Tadalafil works, unlike some other erectile dysfunction medicines. Drinking a lot of alcohol while taking Cialis can increase the risk of side effects, such as dizziness, headache, a faster heart rate and low blood pressure.
Can Cialis be used with other treatments for ED?
The safety and effectiveness of using Cialis with other ED medicines hasn't been studied. Taking them together could lower your blood pressure to dangerously low levels or cause other serious health problems. For this reason, we don't advise taking other ED medicines with Cialis.
Our Clinical Authors
This page has been written by a registered UK pharmacist and reviewed by our clinical team to ensure it is accurate, clear and reflects current clinical guidance.
Last medically reviewed: 05 November 2026
Last updated: 05 November 2026