Sexual health

Tadalafil Side Effects: What the FDA Label Reports

Tadalafil side effects by dose from the FDA label, the nitrate contraindication in full, what the 36 hour figure actually means, and when to seek help.

By Juan Montes Updated October 3, 2026 · 6 min read

Figures below come from the FDA approved prescribing information for tadalafil. The label is linked at the bottom.

This page is general information, not medical advice. It does not replace the prescribing information supplied with your medication or a conversation with the clinician who prescribed it. If you are experiencing symptoms, contact your prescriber.

The one that is not a side effect but will kill you

Starting here because it matters more than anything else on the page. Tadalafil is contraindicated with nitrates. Not cautioned. Contraindicated. From the label:

“Administration of [tadalafil] to patients who are using any form of organic nitrate, either regularly and/or intermittently, is contraindicated.”

Nitrates include nitroglycerin in any form, including the spray or tablets people carry for chest pain, and isosorbide. The combination can drop blood pressure catastrophically.

The same applies to guanylate cyclase stimulators such as riociguat, a pulmonary hypertension drug. The label states: “Do not use [tadalafil] in patients who are using a GC stimulator, such as riociguat.”

If you take nitrates for a heart condition, this class of medication is not a matter of weighing pros and cons with a prescriber. Tell any clinician about every heart medication you take, including ones you use only occasionally.

The common side effects, with the label numbers

The label summarises them as: “Most common adverse reactions (at least 2%) include headache, dyspepsia, back pain, myalgia, nasal congestion, flushing, and pain in limb.”

Taken as needed

Adverse reaction	Placebo	5 mg	10 mg	20 mg
Headache	5%	11%	11%	15%
Dyspepsia (indigestion)	1%	4%	8%	10%
Back pain	3%	3%	5%	6%
Myalgia (muscle ache)	1%	1%	4%	3%
Nasal congestion	1%	2%	3%	3%
Flushing	1%	2%	3%	3%
Pain in limb	1%	1%	3%	3%

Taken once daily at lower dose

Adverse reaction	Placebo	2.5 mg	5 mg
Headache	5%	3%	6%
Dyspepsia	2%	4%	5%
Back pain	1%	3%	3%
Myalgia	1%	2%	2%

Two things worth noticing. The effects are clearly dose related, headache roughly triples from placebo to 20 mg. And the daily low dose regimen produces rates close to placebo, which is a genuine option to discuss if the as needed dose is uncomfortable.

Back pain and muscle ache are characteristic of this drug and often surprise people, because they do not sound like a side effect of an ED medication. They typically appear 12 to 24 hours after dosing and resolve within a couple of days.

The serious ones

Uncommon, but these are the reasons the label runs to fourteen warning sections.

Prolonged erection and priapism

“There have been rare reports of prolonged erections greater than 4 hours and priapism (painful erections greater than 6 hours in duration) for this class of compounds.”

An erection lasting more than four hours is an emergency room visit, not a wait and see. Untreated priapism can cause permanent tissue damage. The label flags particular caution for people with sickle cell disease, multiple myeloma, leukaemia, or anatomical deformation of the penis.

Sudden vision loss

The label covers non-arteritic anterior ischemic optic neuropathy, or NAION, which is a loss of blood flow to the optic nerve. Observational studies suggest an approximately two-fold increase in risk with this drug class, though the label is clear that causation is not established.

For scale, the label puts the background annual rate at 2.5 to 11.8 cases per 100,000 men aged 50 and over. Doubling a rate that small is still a small number, which is the honest way to read it. Sudden loss of vision in one or both eyes means stop and seek medical attention.

Sudden hearing loss

Reported in temporal association with this drug class, sometimes with ringing in the ears and dizziness. Causation again not established. Same instruction: stop and seek prompt attention.

Alpha blockers and blood pressure

Both alpha blockers and this drug class widen blood vessels, so together they can drop blood pressure enough to cause fainting. The label states plainly that tadalafil “is not recommended for use in combination with alpha-blockers for the treatment of BPH”. For ED, the guidance is to be stable on the alpha blocker first and start at the lowest dose.

The full warning list also covers cardiovascular considerations, renal and hepatic impairment, alcohol, potent CYP3A4 inhibitors, combining with other ED treatments, and effects on bleeding.

About the 36 hours

The figure is real and it is in the label, but it is routinely misdescribed. Section 2.1 says tadalafil taken as needed “was shown to improve erectile function compared to placebo up to 36 hours following dosing.”

That means the medication remains capable of working for that long. It does not mean a 36 hour erection, and it does not mean 36 hours of continuous effect. It also has a practical consequence people miss: the nitrate interaction does not end when the effect subsides. The label reports the interaction was no longer detectable at 48 hours.

Who should not take it

Anyone using nitrates in any form. Covered above.
Anyone using a guanylate cyclase stimulator such as riociguat.
Anyone with a known serious hypersensitivity. The label notes Stevens-Johnson syndrome and exfoliative dermatitis have been reported.

Beyond the formal contraindications, the label raises cardiovascular status as a real consideration, because sexual activity itself carries cardiac risk for some people. That is a conversation to have honestly rather than to route around.

How it compares to the alternative

The other common option is sildenafil, which is a shorter acting drug in the same class with a different side effect emphasis. Tadalafil skews toward back pain and muscle ache; sildenafil skews toward flushing and visual disturbance. Neither is better in general. The two are compared in sildenafil versus tadalafil.

A note on where you buy it

This is a category with a real counterfeit problem, and the FDA maintains a running list of sexual enhancement products found to contain undeclared prescription drugs. Its own summary: these products “pose a serious health risk and are not guaranteed to work”, and are “sometimes falsely advertised as dietary supplements, food and/or all-natural treatments.”

The specific danger is that a product sold as natural may contain undeclared tadalafil or sildenafil, which means somebody taking nitrates has no way to know they are at risk. The FDA also notes its list “covers only a small fraction of the contaminated products on the market.”

Separately, in September 2025 the FDA issued warning letters to several telehealth sellers of compounded ED medication. Worth being precise about what those letters said, because it is often reported loosely: the FDA’s stated basis was misbranding through misleading equivalence claims, marketing language implying a compounded product is the same as an FDA approved one, not a finding that the products were unsafe.

Questions worth asking

Do any of my medications count as a nitrate, including anything I only take occasionally?
Given my cardiovascular history, is sexual activity itself something we should assess first?
Would the daily low dose suit me better than the as needed dose?
Am I being dispensed an FDA approved product or a compounded one, and which pharmacy makes it?
What should I do if an erection lasts more than four hours?

Sources

Every figure and quotation on this page comes from the documents below.

FDA, Prescribing information for tadalafil tablets, revised 02/2018. View label
FDA, Sexual Enhancement and Energy Product Notifications. View source
FDA MedWatch, Safety Information and Adverse Event Reporting Program. View source
Burnett AL, Nehra A, Breau RH, et al. Erectile Dysfunction: AUA Guideline. J Urol. 2018;200(3):633-641. View guideline

Last reviewed 10 September 2026. Prescribing information is revised periodically. Check the label directly if you are reading this well after that date.

ED Plans From PrescribedRX

PrescribedRX prescribes ED treatment through clinicians licensed in your state:

Prime Time. Prescription tablets.
Prime Time Max. Higher strength tablets.
The Epiq Chew. A chewable option.

Every plan and its current price is on the plans page and the pricing page.

These are compounded preparations. Compounded drugs are not reviewed or approved by the FDA for safety or effectiveness, and treatment outcomes are not guaranteed.

This article is for general information. It is not medical advice and it is not a recommendation for any particular treatment. Whether a treatment is appropriate for you is a decision for a licensed clinician who has reviewed your health history and current medications.

About the author

Juan Montes

Juan Montes writes and reviews PrescribedRX's clinical content, covering testosterone replacement therapy, men's sexual health, weight management and hair loss. He trained as a Professional Nurse at the Colombian Red Cross in Cali, Colombia, and has worked in healthcare since 2011, roughly six of those years in direct emergency and critical care nursing. He served as Head Nurse in Emergency…