Tadalafil is a long-acting PDE5 inhibitor prescribed for erectile dysfunction, and in some formulations for the urinary symptoms of an enlarged prostate. It is sold under the brand name Cialis® and is also available as a generic and, from some pharmacies, as a compounded troche. Like any medication, it comes with an expected list of common side effects along with a short list of rare but serious warnings that are worth understanding before starting treatment. This article walks through what the prescribing information says about common side effects, the warnings that matter most, the drug interactions that raise risk, and the specific situations that call for contacting a clinician right away.
This article is patient education, not medical advice. It does not create a doctor-patient relationship and is not a substitute for an individualized evaluation from a licensed clinician.
How tadalafil works
Tadalafil belongs to a class of medications called PDE5 inhibitors. An erection depends on healthy blood flow into the penis, and PDE5 inhibitors support that process by relaxing smooth muscle in the walls of blood vessels, which widens them and allows more blood to flow in response to sexual stimulation. The medication does not create desire or produce an erection on its own; sexual stimulation is still required for it to have its intended effect.
Mechanically, PDE5 inhibitors work by blocking an enzyme called phosphodiesterase type 5, which normally breaks down a signaling molecule involved in relaxing smooth muscle. By slowing that breakdown, tadalafil allows the relaxing signal to last longer in response to arousal, which is what supports blood flow into the penis. The same enzyme is present, in smaller amounts, in smooth muscle elsewhere in the body, including blood vessel walls generally and tissue in the digestive tract, which is the basis for most of the side effects covered below.
That same smooth-muscle-relaxing action is not limited to the blood vessels involved in an erection, and it is the reason tadalafil has a predictable side-effect profile. Widening blood vessels elsewhere in the body, easing muscle tissue in the digestive tract, and a long duration of action (tadalafil has a half-life of roughly 17.5 hours, according to the prescribing information) together explain most of what shows up on the label. That long half-life is also what sets tadalafil apart from some other PDE5 inhibitors: it is part of why some formulations are approved for daily use at a low dose rather than only as needed, and it is also why side effects, when they occur, can sometimes linger longer than a shorter-acting medication's would.
Common side effects
Common side effects in the tadalafil prescribing information include headache, indigestion, back pain, muscle aches, flushing and nasal congestion. Headache and indigestion are generally the most frequently reported, and most people who experience them describe them as mild to moderate rather than severe. Flushing (a warm, reddened feeling in the face or chest) and nasal congestion are also related to the medication's effect on blood vessels, and both tend to pass on their own within a few hours.
Back pain and muscle aches are reported often enough, and distinctly enough from a typical muscle strain, that they are worth knowing about in advance. Back pain and muscle aches typically appear 12 to 24 hours after a dose and resolve within about 48 hours, according to the label. That delayed onset, well after the dose rather than immediately following it, is a useful detail: it is one reason clinicians can often reassure a patient that a new ache fits the medication's known pattern rather than signaling something else, though any new or severe pain is still worth mentioning at a follow-up.
None of these common effects require stopping treatment on their own, and many people taking tadalafil do not experience them at all or find them mild enough to not think twice about. They are, however, exactly the kind of thing to mention to a clinician if they are frequent, severe, or disruptive, since dose and timing can sometimes be adjusted.
How a given person experiences tadalafil can vary with dose and with the formulation prescribed, whether that is an as-needed dose taken before sexual activity or a lower daily dose. A clinician who knows your full health picture, including kidney and liver function, age, and other medications, is in the best position to weigh dose against side-effect risk; this is not something to estimate from a label alone. If a side effect shows up consistently at one dose, that is useful information to bring to a follow-up rather than something to simply tolerate indefinitely.
| Category | What the label reports |
|---|---|
| Common | Headache, indigestion, back pain, muscle aches, flushing, nasal congestion |
| Typical timing | Back pain and muscle aches often appear 12 to 24 hours after a dose and resolve within about 48 hours |
| Rare but serious | Sudden vision loss, sudden hearing loss, an erection lasting more than 4 hours |
| Key interaction warning | Contraindicated with nitrates; caution with alpha blockers and some other medicines |
| Before any prescription | A clinician reviews health history and current medications; eligibility is never guaranteed |
Rare but serious warnings
Most people who take tadalafil never experience the effects in this section, but they are serious enough that everyone taking the medication should know what they look like. Sudden vision loss or sudden hearing loss are rare reported events that need immediate medical attention. Vision changes can include blurred vision, loss of vision in one or both eyes, or a sudden change in color vision; hearing changes can include ringing in the ears, dizziness, or a sudden drop in hearing, sometimes along with vision symptoms. Neither is a "wait and see" situation: stop taking the medication and seek emergency medical care right away if either occurs.
The other rare but serious warning involves the medication's core mechanism rather than an unrelated organ system. An erection lasting more than 4 hours is a medical emergency. This is known as priapism, and it can cause permanent damage to the tissue of the penis if it is not treated promptly. An erection that persists well beyond the usual response to stimulation, or that becomes painful, is not something to ride out at home; it needs emergency evaluation the same day.
Being able to recognize these two warnings, and knowing to act immediately rather than waiting for a routine follow-up, is part of what a clinician reviews before and during treatment. Reporting any of these symptoms promptly, even if they resolve on their own, is still worth a call to your prescribing clinician afterward.
Drug interactions that raise risk
Tadalafil is contraindicated with nitrates and has important interaction warnings with alpha blockers and some other medicines. Nitrates, prescribed for chest pain in forms like nitroglycerin tablets, patches and sprays, work through a related pathway that also relaxes blood vessels. Combined with tadalafil, that overlap can cause a sudden, dangerous drop in blood pressure. "Nitrates" includes occasional or as-needed use, and it also includes some recreational substances sometimes called poppers; there is no safe dose of a nitrate to combine with tadalafil.
Alpha blockers, commonly prescribed for high blood pressure or for the urinary symptoms of an enlarged prostate, are not an absolute contraindication the way nitrates are, but they do require clinician oversight on dosing and timing, since the combination can lower blood pressure further than either medication alone. Other blood pressure medicines, certain HIV and hepatitis C antiviral medications, and some antifungal medications can also change how much tadalafil is in your system or how it interacts with blood pressure, which is why a complete medication list matters as much as the tadalafil prescription itself.
Alcohol is not a medication, but it lowers blood pressure in a similar direction, and combining a lot of alcohol with tadalafil can add to lightheadedness or a drop in blood pressure on standing. Our guide to ED medications and alcohol covers that combination in more detail, and our broader rundown of ED medications and drug interactions goes through other combinations clinicians screen for.
Because tadalafil's effects can last well beyond a single day, the timing advice that works for a shorter-acting medication does not automatically apply here. A combination that would be fine the next morning with a shorter-acting option may still overlap with tadalafil, which is part of why disclosing tadalafil use matters in an emergency: if nitrates might be needed for chest pain, emergency clinicians need to know a PDE5 inhibitor is in your system and roughly when it was last taken. None of this is a reason to avoid tadalafil altogether; it is a reason to make sure your full medication list, including anything used only occasionally, reaches the clinician reviewing your care.
When to contact a clinician
Most tadalafil side effects are mild, predictable from the label, and not a reason to stop treatment on their own. Still, there is a clear line between "worth mentioning at your next check-in" and "call now." Sudden vision or hearing loss, an erection lasting more than 4 hours, chest pain, or fainting after a dose all belong in the second category, and warrant immediate medical attention rather than waiting. Severe or worsening back pain, side effects that interfere with daily life, or any symptom that feels different from what the label describes are worth a call to your prescribing clinician even if they are not an emergency.
Before any prescription is written, a clinician reviews your health history, current medications (including anything taken only occasionally, like an as-needed nitrate), and relevant cardiovascular history to determine whether tadalafil is appropriate and at what dose. That review happens through a confidential online medical history questionnaire, and if treatment is appropriate, it is dispensed through a licensed U.S. pharmacy. Being thorough about your medication list, including supplements, is what actually lets a clinician weigh the interaction risks covered above.
If you are weighing tadalafil against a shorter-acting option, our comparison of sildenafil vs tadalafil covers how the two differ, and our explainer on tadalafil and blood pressure goes deeper into the cardiovascular interactions above. You can find more on related topics in our ED & Blood Flow section, including how ED medications work as a class.
The larger point across all of this is that tadalafil's side-effect profile is well characterized, and most of what people experience fits squarely within the common, predictable category described above. The rare but serious warnings exist precisely because they fall outside that pattern, which is exactly why they deserve to be recognized quickly rather than waited out. A thorough online evaluation, reviewed by an independent licensed clinician, is what turns a general label into a decision that fits your specific health history, current medications, and goals, and it is the step that comes before any prescription, not after.
Important Safety Information
Indication. Tadalafil is a PDE5 inhibitor prescribed to treat erectile dysfunction, and in some formulations to treat the urinary symptoms of benign prostatic hyperplasia. It requires sexual stimulation to have its intended effect and does not increase sexual desire on its own.
Common side effects. Headache, indigestion, back pain, muscle aches, flushing and nasal congestion are among the more commonly reported side effects. Back pain and muscle aches typically appear 12 to 24 hours after a dose and resolve within about 48 hours.
Warnings. Tadalafil is contraindicated with nitrates due to the risk of a dangerous drop in blood pressure, and it has important interaction warnings with alpha blockers and some other medicines. Rare but serious risks include a prolonged, painful erection (priapism) requiring immediate medical attention, and sudden vision or hearing loss. Tell your clinician about your full health history and all medications before starting treatment.
Talk to your doctor. This information is educational and is not a substitute for medical advice. Only a licensed medical professional can determine whether a treatment is right for you. Talk to your doctor about the benefits and risks, and report any side effects.
Frequently asked questions
What are the most common tadalafil side effects?
Common side effects in the tadalafil prescribing information include headache, indigestion, back pain, muscle aches, flushing and nasal congestion. Most of these are mild to moderate and pass on their own.
Why does tadalafil cause back pain and muscle aches?
Back pain and muscle aches typically appear 12 to 24 hours after a dose and resolve within about 48 hours, according to the label. That delayed timing is a known pattern for tadalafil rather than a sign of a muscle strain, though any severe or unusual pain is still worth mentioning to a clinician.
What drug interactions should I know about with tadalafil?
Tadalafil is contraindicated with nitrates and has important interaction warnings with alpha blockers and some other medicines. Nitrates, including occasional use, must never be combined with tadalafil because of the risk of a dangerous drop in blood pressure, and alpha blockers need clinician oversight on dosing and timing.
What are the rare but serious tadalafil side effects?
Sudden vision loss or sudden hearing loss are rare reported events that need immediate medical attention. These are uncommon, but anyone taking tadalafil should know to stop the medication and seek emergency care right away if either occurs.
What should I do if an erection lasts more than 4 hours?
An erection lasting more than 4 hours is a medical emergency. This is known as priapism and can cause permanent damage if not treated promptly, so it needs emergency evaluation the same day rather than being managed at home.
