Short answer: In the label's placebo-controlled trials of Cialis taken as needed for ED, the most common side effects were headache (11% to 15% vs 5% on placebo), indigestion (4% to 10% vs 1%), back pain (3% to 6% vs 3%), muscle aches, nasal congestion and flushing. Back pain and muscle aches usually started 12 to 24 hours after a dose. Cialis has no boxed warning.
What Cialis is approved for: Cialis is approved to treat erectile dysfunction (ED), the signs and symptoms of benign prostatic hyperplasia (BPH), and ED with BPH together. When started with finasteride for BPH, use is recommended for up to 26 weeks (section 1).
Source
CIALIS (tadalafil) tablets, prescribing information and Patient Information. Eli Lilly. DailyMed, version published June 10, 2026. DailyMed setid bcd8f8ab-81a2-4891-83db-24a0b0e25895
No. The current Cialis label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Cialis.
| Adverse reaction | Placebo (N=476) | Tadalafil 5 mg (N=151) | Tadalafil 10 mg (N=394) | Tadalafil 20 mg (N=635) |
|---|---|---|---|---|
| Headache | 5% | 11% | 11% | 15% |
| Dyspepsia | 1% | 4% | 8% | 10% |
| Back pain | 3% | 3% | 5% | 6% |
| Myalgia | 1% | 1% | 4% | 3% |
| Nasal congestion | 1% | 2% | 3% | 3% |
| Flushing (a) | 1% | 2% | 3% | 3% |
| Pain in limb | 1% | 1% | 3% | 3% |
Eight 12-week placebo-controlled studies of Cialis taken as needed for ED; mean age 59 (range 22 to 88). Stopping because of side effects: 3.1% on 10 or 20 mg vs 1.4% on placebo. (a) Flushing includes facial flushing and flushing.
| Adverse reaction | Placebo (N=576) | Tadalafil 5 mg (N=581) |
|---|---|---|
| Headache | 2.3% | 4.1% |
| Dyspepsia | 0.2% | 2.4% |
| Back pain | 1.4% | 2.4% |
| Nasopharyngitis | 1.6% | 2.1% |
| Diarrhea | 1.0% | 1.4% |
| Pain in extremity | 0.0% | 1.4% |
| Myalgia | 0.3% | 1.2% |
| Dizziness | 0.5% | 1.0% |
Three 12-week placebo-controlled trials of Cialis 5 mg once daily, two in men with BPH and one in men with ED and BPH; mean age 63 (range 44 to 93). Stopping because of side effects: 3.6% on Cialis vs 1.6% on placebo.
Once daily for ED, 12-week trials (Table 2; placebo, 2.5 mg, 5 mg): headache 5%, 3%, 6%; indigestion 2%, 4%, 5%; nasopharyngitis 4%, 4%, 3%; back pain 1%, 3%, 3%; upper respiratory infection 1%, 3%, 3%; flushing 1%, 1%, 3%. Stopping because of side effects: 4.1% vs 2.8% on placebo.
Back pain or muscle aches generally began 12 to 24 hours after a dose and usually resolved within 48 hours. About 0.5% of people taking Cialis as needed stopped because of them. In the 1-year open-label extension, back pain was reported in 5.5% and muscle aches in 1.3%.
Diarrhea was reported more often in people 65 and older taking Cialis as needed (2.5%). Changes in color vision were rare across all studies (<0.1% of patients).
Two observational studies suggested about a 2-fold higher risk of NAION (a sudden optic nerve problem) right after PDE5 inhibitor use, with risk estimates of 2.15 (95% CI 1.06, 4.34) and 2.27 (95% CI 0.99, 5.20). The label says this does not establish cause.
In a clinical pharmacology study, tadalafil 20 mg lowered supine blood pressure by a mean maximum of 1.6/0.8 mm Hg more than placebo in healthy subjects.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Do not use with nitrates or riociguat. Cialis must not be used with any form of organic nitrate, used regularly or now and then, or with guanylate cyclase stimulators such as riociguat, because blood pressure can drop sharply. It is also contraindicated after a known serious allergy to tadalafil (Cialis or ADCIRCA).
Heart risk with sexual activity. Cialis is not for men whose heart condition makes sexual activity inadvisable. It is not recommended after a heart attack in the last 90 days, unstable angina or angina during sex, NYHA Class 2 or greater heart failure in the last 6 months, uncontrolled arrhythmias, low blood pressure (<90/50 mm Hg), uncontrolled high blood pressure, or a stroke in the last 6 months. If a nitrate is needed in a life-threatening emergency, at least 48 hours should pass after the last Cialis dose.
Interactions with once daily use. Once daily Cialis keeps tadalafil in the blood continuously, which matters for interactions with nitrates, alpha-blockers, blood pressure medicines, potent CYP3A4 inhibitors and heavy alcohol use.
Prolonged erection. Rare erections lasting more than 4 hours and priapism (painful erections over 6 hours) have been reported. An erection lasting more than 4 hours needs emergency care, as untreated priapism can permanently damage the penis.
Sudden vision loss. Sudden loss of vision in one or both eyes may be a sign of NAION. The label says to stop all PDE5 inhibitors, including Cialis, and get medical attention. It is not recommended for people with inherited retinal disorders such as retinitis pigmentosa.
Sudden hearing loss. Sudden decrease or loss of hearing, sometimes with ringing in the ears and dizziness, has been reported. The label says to stop Cialis and get prompt medical attention.
Alpha-blockers and blood pressure medicines. Cialis can add to the blood-pressure-lowering effect of these medicines, which may cause fainting. For BPH, Cialis with an alpha-blocker is not recommended, and an alpha-blocker for BPH is stopped at least one day before starting once daily Cialis for BPH.
Kidney impairment. Lower doses or longer gaps between doses are needed with reduced kidney function, and once daily use is not recommended when creatinine clearance is below 30 mL/min (see the dosing page).
Liver impairment. With mild or moderate liver impairment the dose should not exceed 10 mg; use in severe liver impairment is not recommended.
Alcohol. Substantial alcohol (for example 5 units or more) with Cialis can raise the chance of a faster heart rate, lower standing blood pressure, dizziness and headache.
Potent CYP3A4 inhibitors. Drugs such as ritonavir, ketoconazole and itraconazole raise tadalafil levels, so the label lowers the maximum Cialis dose with them.
Other ED treatments. Cialis has not been studied with other PDE5 inhibitors or ED treatments, and should not be taken with other PDE5 inhibitors, including ADCIRCA.
Bleeding. Cialis has not been given to people with bleeding disorders or significant active stomach ulcers; use in them calls for careful weighing of risk and benefit.
Sexually transmitted diseases. Cialis offers no protection against sexually transmitted diseases, including HIV.
Other urinary conditions. Before treating BPH, other urinary conditions with similar symptoms are considered, and prostate cancer and BPH may exist together.
From the Patient Information that comes with Cialis:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.