Cialis side effects: A complete guide for UK patients
- The most common Cialis side effects and how frequently they occur
- How Cialis side effects compare to Viagra
- Specific questions answered: joint pain, blood pressure, blood in stool, and blood clots
- Serious side effects requiring urgent attention
- When to stop Cialis and seek medical help
- Why does Cialis cause side effects?
- Most common Cialis side effects
- Cialis side effects vs Viagra: How do they compare?
- Cialis and joint pain: Why does it happen?
- Can Cialis cause blood in stool?
- Can Cialis cause blood clots?
- Cialis and blood pressure
- Rare but serious side effects
- How to manage common side effects
- Final thoughts
Why does Cialis cause side effects?
Cialis works by inhibiting PDE5, an enzyme that regulates blood flow in the smooth muscle of blood vessel walls. This produces vasodilation not only in the intended area but to a lesser degree throughout the body. Most of Cialis's common side effects are a direct consequence of this systemic vasodilatory effect. The additional GI effects (indigestion, back pain, muscle aches) reflect tadalafil's partial inhibition of other PDE enzymes, particularly PDE11, which is found in muscle tissue.
Most common Cialis side effects
Frequency data below is drawn from the Cialis Summary of Product Characteristics at medicines.org.uk.
Very common (affecting more than 1 in 10 people)
- Headache: Caused by vasodilation in cranial blood vessels
- Dyspepsia (indigestion): Caused by smooth muscle relaxation in the gastrointestinal tract
- Back pain: Related to PDE11 inhibition in muscle tissue; more specific to tadalafil than other PDE5 inhibitors
- Myalgia (muscle aches): Also linked to PDE11 activity; typically affects the lower back and limbs
- Flushing: Redness and warmth in the face caused by increased peripheral blood flow
- Nasal congestion: Vasodilation in nasal mucosa
Common (affecting 1-10 in 100 people)
- Dizziness, visual disturbances, hypotension, nausea, abdominal pain, and rash
Most effects are mild to moderate, temporary, and more common at the 20 mg dose and in the early weeks of treatment.
Cialis side effects vs Viagra: How do they compare?
| Side effect | Viagra (sildenafil) | Cialis (tadalafil) | Notes |
|---|---|---|---|
| Headache | Very common | Very common | Similar in both |
| Flushing | Very common | Common | More frequent with sildenafil |
| Indigestion | Common | Very common | More frequent with tadalafil |
| Back pain and muscle aches | Not typically reported | Very common | Most distinctive difference |
| Visual disturbances | Common | Less common | More associated with sildenafil |
| Dizziness | Common | Common | Similar in both |
The most clinically meaningful difference is that back pain and muscle aches are significantly more common with tadalafil. Men who experience visual disturbances with sildenafil often find tadalafil better tolerated in this respect.
Cialis and joint pain: Why does it happen?
Joint pain and muscle aches are among the more commonly reported complaints with Cialis, particularly at the 20 mg dose. The mechanism is tadalafil's partial inhibition of PDE11 in skeletal muscle, producing low-level effects typically felt in the lower back, legs, and occasionally joints. These usually appear within 12-24 hours of a dose and resolve within 48 hours.
Good to know
If joint or muscle pain is significantly affecting quality of life, speak to your prescriber about a dose reduction to 10 mg, switching to daily tadalafil at 5 mg, or trying an alternative PDE5 inhibitor.For a full breakdown of available doses and titration guidance, see our Cialis dose guide
Can Cialis cause blood in stool?
Gastrointestinal bleeding is listed as a rare adverse event in the Cialis Summary of Product Characteristics. If you notice blood in your stool while taking Cialis, seek medical assessment rather than attributing it to the medication without investigation. Contact your GP, call NHS 111, or attend your nearest urgent treatment centre if you notice rectal bleeding, black or tarry stools, or blood in vomit.
Warning!
Do not assume GI bleeding is a medication side effect without seeking medical assessment. Blood in stool can indicate conditions unrelated to Cialis that require prompt investigation.
Can Cialis cause blood clots?
No. Blood clots are not listed as a known side effect of Cialis in the MHRA-approved Summary of Product Characteristics, and there is no established clinical evidence linking tadalafil to an increased risk of thrombosis. Tadalafil's mechanism produces vasodilation, the opposite effect to that which produces clot formation.
If you develop symptoms suggestive of a blood clot (sudden leg swelling, redness, warmth, or difficulty breathing), seek urgent medical attention regardless of any medication you are taking.
Cialis and blood pressure
Tadalafil causes a modest reduction in blood pressure as a direct consequence of its vasodilatory mechanism. For most healthy men this is well tolerated, but it can be more pronounced in men taking antihypertensives or alpha-blockers. The absolute contraindication with nitrates is the most serious concern: tadalafil and nitrates both lower blood pressure through different mechanisms, and their combination can produce a severe and potentially life-threatening drop.
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 Cialis.
Rare but serious side effects
The following Cialis (tadalafil) side effects require immediate medical attention:
- Priapism: An erection lasting more than four hours. Go to A&E immediately.
- Sudden vision loss: Attend eye casualty or A&E immediately.
- Sudden hearing loss: Stop taking Cialis and seek prompt medical attention.
- Severe allergic reaction: Swelling of the face, lips, tongue, or throat; difficulty breathing. Call 999 immediately.
Report any suspected serious side effects via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.
How to manage common side effects
- Headache: Stay well hydrated. Paracetamol is generally effective.
- Back pain and muscle aches: Usually resolve within 48 hours. Discuss a dose reduction with your prescriber if persistent.
- Indigestion: Take with water rather than on a full stomach. Stay upright for 30 minutes after taking the tablet.
- Flushing and nasal congestion: Usually mild and self-limiting. Reducing alcohol intake helps, as alcohol compounds vasodilation.
- Dizziness: Stand up slowly from sitting or lying positions.
Final thoughts
Cialis is well tolerated by most men who are appropriately assessed before starting. Back pain and muscle aches are its most distinctive side effects compared to other PDE5 inhibitors, but for most men these are mild and short-lived. The key safety principles are straightforward: disclose all medications to your prescriber, never take Cialis with nitrates, and seek urgent medical attention if any serious warning signs occur.
DoktorABC connects UK patients with licensed prescribers who can assess suitability for Cialis and provide ongoing clinical guidance.
FAQ
What are the most common Cialis side effects?
Headache, indigestion, back pain, muscle aches, facial flushing, and nasal congestion. Most are mild and temporary.
How do Cialis side effects compare to Viagra?
Back pain and muscle aches are significantly more common with Cialis. Visual disturbances are more associated with Viagra. Neither is clearly better tolerated across all measures.
Why does Cialis cause back pain and joint pain?
Tadalafil partially inhibits PDE11 in skeletal muscle tissue, producing low-level effects typically felt in the lower back and legs. These usually resolve within 48 hours.
Can Cialis cause blood in stool?
Gastrointestinal bleeding is a rare adverse event. If you notice blood in your stool, seek medical assessment promptly rather than attributing it to the medication without investigation.
Can Cialis cause blood clots?
No. Blood clots are not a known side effect of tadalafil, and there is no established clinical evidence linking Cialis to increased thrombosis risk.
Does Cialis lower blood pressure?
Yes, modestly. This is not significant for most men but can be more pronounced in those taking antihypertensives or alpha-blockers. Tadalafil must never be taken with nitrates.
Where can I report a side effect from Cialis?
Via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk, through the Yellow Card app, or by asking your prescriber or pharmacist to report on your behalf.
The DoktorABC medical advisory board
Dr. Roland Ruiken
Medical advisor, Norway
Dr. Viktor Simunovic
Medical advisor, Croatia