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Cialis 20 mg: Uses, Benefits, Side Effects & More

Mike Bohl, MD, MPH, ALM

Reviewed by Mike Bohl, MD

Written by Vanessa Gibbs

Published 12/21/2021

Updated 01/16/2024

You might have seen Cialis® — the erectile dysfunction (ED) drug — available in doses ranging from 2.5 mg to 20 mg. Surely, more is better right? 

Well, not always. Cialis 20 mg is an effective erectile dysfunction treatment, but so are the lower doses. 

Below, we’ve covered what Cialis 20 mg is used for, the benefits and side effects of this dose of Cialis and how it stands up against other strengths. 

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What Is Cialis 20 mg Used for? 

Cialis is the brand name for tadalafil. Tadalafil is a phosphodiesterase type 5 inhibitor or, if you want less of a mouthful, a PDE5 inhibitor. 

Cialis is FDA-approved to treat

  • Erectile dysfunction 

  • Benign prostatic hyperplasia (BPH), or an enlarged prostate 

Cialis dosages include 2.5 mg, 5 mg, 10 mg and 20 mg. 

You can take Cialis on an as-needed basis and pop a pill before sex, or you can take a daily dose of Cialis, so you’re always ready for action. 

If you’re taking it as needed, you’re likely going to be prescribed 5mg, 10mg or 20mg. 10mg is the typical starting dose, and it can be adjusted up or down depending on efficacy and side effects. 

But you won’t be taking 20 mg Cialis daily. Daily doses of Cialis are the lower doses of 2.5 mg and 5 mg.

How does Cialis work? For ED — which is when you struggle to get or keep an erection — Cialis works by dilating the blood vessels in the penis, which leads to a firmer erection. 

Cialis — 20 mg or otherwise — doesn’t just give you an erection though. Some form of sexual stimulation is required to get hard.

Cialis 20 mg may be a more effective treatment of ED than the 10 mg version. Clinical trials found that 68 percent to 77 percent of men taking 10 mg Cialis were able to have penetrative sex with their partner. Of those taking 20 mg Cialis, 76 percent to 85 percent were able to have penetrative sex. 

But not all research agrees — a smaller daily dose may be just as effective as the as-needed Cialis treatment. 

A systematic review and meta-analysis looked at six randomized controlled trials with a total of over 1,500 patients and compared an as-needed tadalafil treatment to a once-a-day dose. The results showed that both treatments had about the same effectiveness.

Tadalafil can also be used to treat pulmonary arterial hypertension, a form of high blood pressure that affects the blood vessels in the lungs. 

A 20 mg dose may come in handy here. A 2006 study found that a single dose of 20 mg of tadalafil lowered average blood pressure over 26 hours in patients with uncontrolled high blood pressure. 

You can learn more in our guide to tadalafil uses

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The Benefits of Cialis 

Cialis benefits include: 

  • Cialis lasts a long time. While Cialis is just as effective as Viagra, 20mg Cialis lasts longer in your body and is known as the “weekend pill” for a reason. Because you can pop one pill and have sex whenever you like over the next 36 hours (give or take a few hours), it offers more spontaneity.
    In comparison, avanafil only lasts up to six hours and Viagra® only lasts up to four hours. 

  • Cialis is effective. Clinical trials show that Cialis can be effective for all severities and types of ED, including difficult-to-treat ED. If you find Cialis 10 mg isn’t working for you, a Cialis 20 mg tablet might do the trick. 

  • You don’t need to take it every day. Depending on your preference and lifestyle, you may not want to take Cialis day in and day out. In fact, the 20mg dose should only be taken as needed. 

  • Side effects are typically mild. Side effects of Cialis are usually mild and should go away on their own — although they may be worse with higher doses. For example, research shows that 11 percent of people taking tadalafil 10 mg got a headache, whereas 15 percent of those taking tadalafil 20 mg got a headache.
    Some side effects have the same likelihood in both doses, such as flushing and limb pain. If the side effects of Cialis 20 mg are too much, a healthcare provider may reduce your dose.

  • Less flushing. If this is a particularly annoying side effect of ED drugs for you, switching to Cialis may be the answer. A 2017 systematic review and meta-analysis compared sildenafil (the generic of Viagra) and tadalafil. It found that tadalafil caused lower rates of flushing.
    Muscle aches and back pain were more common in tadalafil than sildenafil, though. You can’t win ‘em all. Overall, tadalafil and sildenafil had similar efficacy and safety, but men and their partners tended to prefer tadalafil. You can learn more about the two ED treatments in our Cialis vs. Viagra guide.

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Cialis 20 mg Side Effects and Interactions 

As with any drug, Cialis comes with possible side effects. 

The most common Cialis side effects include: 

  • Headache

  • Dyspepsia (indigestion) 

  • Back pain 

  • Myalgia (muscle aches and pain)

  • Nasal congestion 

  • Flushing 

  • Limb pain 

Depending on the side effect, they may happen in as little as three percent of people taking Cialis 10 mg or Cialis 20 mg.  

Clinical trials show that most side effects are dose-dependent, meaning you’re more likely to get them with higher doses — AKA Cialis 20 mg. 

An allergic reaction to Cialis is also possible. In this case, you may experience: 

  • Rash

  • Hives 

  • Swelling of the lips, tongue or throat

  • Difficulty breathing or swallowing 

There’s also a risk of priapism, or prolonged erections — we’re talking for several hours here. It may sound great if you’re suffering from ED, but prolonged erections can actually be painful and cause irreversible damage to the penis. 

If your erection lasts more than four hours, seek medical advice. 

You may be more likely to get prolonged erections from Cialis if you have: 

  • Sickle cell anemia

  • Multiple myeloma 

  • Leukemia 

  • Anatomic deformations in the penis (like Peyronie’s disease)

Our guide to priapism provides more information about this side effect, as well as what you can do if you think you’re affected.

There’s also a small risk of vision loss. If you notice any vision loss in one or both eyes, stop taking Cialis and seek medical help. This could be a sign of a condition called non-arteritic anterior ischemic optic neuropathy (NAION), which is caused by a lack of blood flow to the optic nerve. 

Another serious side effect includes a sudden decrease in hearing or hearing loss. Again, get medical advice ASAP if you notice this.

There are also a few drug interactions you should know about.

You shouldn’t take Cialis at all if you’re taking nitrates. The combo can cause your blood pressure to drop suddenly, resulting in dizziness, loss of consciousness or even a heart attack or stroke. Nitrates can be found in medications like isosorbide dinitrate or isosorbide mononitrate. 

Also watch out for recreational drugs that contain nitrates like “poppers.” 

You also shouldn’t take Cialis if you take medications called guanylate cyclase stimulators, such as riociguat. 

You may be prescribed a low dose of Cialis — so probably not the 20 mg kind — if you’re taking alpha-blockers (like doxazosin, tamsulosin or alfuzosin) or CYP3A4 inhibitors (like the antibiotic erythromycin and the antifungal med ketoconazole). 

It’s unclear whether it’s safe to take Cialis with other PDE5 inhibitors such as: 

  • Viagra (sildenafil) 

  • Levitra® (vardenafil) 

  • Stendra® (avanafil) 

Be sure to tell your prescribing healthcare provider about any medications or supplements you take before trying Cialis. 

Beyond meds, watch out for how much you drink when you’re taking Cialis.

If you drink five units or more of alcohol, you may experience:

  • Increased heart rate

  • Decreased standing blood pressure

  • Dizziness

  • Headache 

And a weird one to watch out for: grapefruit and Cialis 

A 2020 study on rats found that grapefruit juice inhibits the metabolism of tadalafil — remember that’s the active ingredient in Cialis. This can lead to you having more tadalafil in your system, which can increase your risk of side effects.

You can learn more about what to avoid in our guide on tadalafil interactions.  

Finally, tell a healthcare provider about any and all medical conditions you have before taking Cialis, so they can determine whether it’s safe for you. 

This includes if you have: 

  • Heart problems like angina (chest pain caused by reduced blood flow to the heart), heart disease or irregular heartbeats 

  • Low blood pressure

  • Stomach ulcers 

  • Retinitis pigmentosa (a genetic eye disease)

Cialis 20 mg vs. Other Cialis Dosages 

Cialis is available in a range of doses. Here’s what they’re usually prescribed for:  

  • Cialis 2.5 mg. If you’re taking Cialis daily, you’ll might be prescribed a 2.5 mg dose. This may be increased to 5 mg if 2.5 mg isn’t effective and you don’t have any bothersome side effects.

  • Cialis 5mg. For BPH, you may be prescribed a 5 mg daily dose of Cialis. If you have both BPH and ED (the two conditions are linked), you may get a 5 mg daily dose of Cialis as well. 

  • Cialis 10 mg. For an as-needed ED treatment, you’ll most likely be prescribed a 10 mg dose of Cialis to get started. A healthcare provider may then increase your dose to 20 mg or decrease it to 5 mg, depending on how you react to the drug and how well it works for you. 

  • Cialis 20 mg. The big daddy. You’ll most likely only be prescribed Cialis 20 mg as an as-needed ED treatment if you’ve got on well with a 10 mg dose but found that it wasn’t working well enough for you. 

There are upsides and downsides to each tadalafil dosage, whether you're taking 20mg Cialis or a lower dose. The recommended daily dose starts at 2.5mg and may be increased to 5mg if this dosage isn't effective.

For example, one benefit of the smaller daily dose of Cialis is that you’ll be ready to go at any time. But the downsides are you’ll need to remember to take the daily medication and you may experience more persistent side effects. Check our guide to daily-use Cialis to learn more.

The benefit of a higher-dose as-needed treatment is you don’t have to take Cialis every day, so you don’t have to worry about missed doses. Plus, higher doses have been shown to be more effective. But the higher the dose you take, the more likely it is that you’ll experience side effects. 

A healthcare provider can recommend the best Cialis dosage for you.

FYI: You can’t buy Cialis over the counter. You’ll need to talk with a healthcare professional and get the ED drug prescribed. 

As tempting as they can be, steer clear of non-prescription Cialis substitutes. They’re not approved by the Food and Drug Administration (FDA) and some fake PDE5 inhibitors have been found to contain contaminants.

They’ve also been found to contain anywhere from zero percent to more than 200 percent of the labeled dose of active ingredients. This could cause some serious health problems. 

Just one glance at the FDA’s database of tainted sexual enhancement products will show you that many contain hidden ingredients. Yikes. 

How to Take Cialis 20 mg 

If you’re taking Cialis before sexual activity, take your prescribed dose — whether that’s 20 mg or a smaller dose — at least 30 minutes to two hours before you plan on getting it on. You don’t need to take Cialis with food. 

Only take Cialis once per day, max. If you plan on having sex more than once — *fist bump* — Cialis has you covered. It’s been shown to improve erectile function for up to 36 hours. 

You can learn more in our guide on how long Cialis lasts

If you’re taking daily Cialis, whether for ED or BPH, take your dose at roughly the same time every day. You don’t need to worry about when you’ll be having sex. 

A healthcare provider will be able to tell you the best way to take Cialis for your individual needs.

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Is Cialis 20 mg Right for You? 

Cialis 20 mg is a treatment option for ED. It might be right for you if you tolerate the 10 mg tablets but aren’t yet getting full benefit. 

A healthcare provider will be able to tell you if Cialis 20 mg is right for you.  

Here's the lowdown: 

  • Cialis 20 mg is an as-needed ED treatment. You’ll take it before having sex, when you need it. It should provide ED relief for up to 36 hours, freeing you up to do your thang.  

  • Side effects are mild. You might get a headache, indigestion or backache. Not ideal when you’re trying to have some sexy time, but these side effects should be mild. Speak to a healthcare provider if any side effects bother you. They may recommend a lower Cialis dose. 

  • Other ED treatments are available. Cialis 20 mg isn’t your only option. There’s Viagra or sildenafil, Stendra and our hard mints, which contain the active ingredients in Cialis, Levitra and Staxyn. 

You’ll need a prescription to get Cialis 20 mg — or any other PDE5 inhibitor. That doesn’t necessarily mean you have to leave the house, though. 

You can connect with one of our licensed healthcare professionals online to find out which erectile dysfunction treatments are right for you and get Cialis — or other ED drugs — delivered to you, if if appropriate.

Learn more about the cost of using Cialis or generic tadalafil to treat ED in our full guide to Cialis pricing.

16 Sources

  1. Highlights of Prescribing Information. (n.d.). https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/021368s030lbl.pdf
  2. Dhaliwal, A., Gupta, M. (2023, April 10). PDE5 Inhibitors - StatPearls. NCBI. https://www.ncbi.nlm.nih.gov/books/NBK549843/
  3. Definition & Facts for Erectile Dysfunction. (n.d.). https://www.niddk.nih.gov/health-information/urologic-diseases/erectile-dysfunction/definition-facts
  4. Peng, Z., Yang, L., Dong, Q., Wei, Q., Liu, L., & Yang, B. (2017). Efficacy and Safety of Tadalafil Once-a-Day versus Tadalafil On-Demand in Patients with Erectile Dysfunction: A Systematic Review and Meta-Analyses. Urologia internationalis, 99(3), 343–352. https://karger.com/uin/article-pdf/99/3/343/3603031/000477496.pdf
  5. Patterson, D., McInnes, G. T., Webster, J., Mitchell, M. M., & Macdonald, T. M. (2006). Influence of a single dose of 20 mg tadalafil, a phosphodiesterase 5 inhibitor, on ambulatory blood pressure in subjects with hypertension. British journal of clinical pharmacology, 62(3), 280–287. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1885145/
  6. Questions and Answers for Cialis (tadalafil). (n.d.). https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/questions-and-answers-cialis-tadalafil
  7. Huang, S. A., & Lie, J. D. (2013). Phosphodiesterase-5 (PDE5) Inhibitors In the Management of Erectile Dysfunction. P & T : a peer-reviewed journal for formulary management, 38(7), 407–419. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3776492/
  8. Katz, E. G., Tan, R. B., Rittenberg, D., & Hellstrom, W. J. (2014). Avanafil for erectile dysfunction in elderly and younger adults: differential pharmacology and clinical utility. Therapeutics and clinical risk management, 10, 701–711. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4155803/
  9. Viagra (sildenafil citrate) tablets. (n.d.). https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/20895s039s042lbl.pdf
  10. Coward, R. M., & Carson, C. C. (2008). Tadalafil in the treatment of erectile dysfunction. Therapeutics and clinical risk management, 4(6), 1315–1330. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2643112/
  11. Gong, B., Ma, M., Xie, W., Yang, X., Huang, Y., Sun, T., Luo, Y., & Huang, J. (2017). Direct comparison of tadalafil with sildenafil for the treatment of erectile dysfunction: a systematic review and meta-analysis. International urology and nephrology, 49(10), 1731–1740. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5603624/
  12. Frajese, G. V., Pozzi, F., & Frajese, G. (2006). Tadalafil in the treatment of erectile dysfunction; an overview of the clinical evidence. Clinical interventions in aging, 1(4), 439–449. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2699638/
  13. ​​Shen, X., Chen, F., Wang, F., Huang, P., & Luo, W. (2020). The Effect of Grapefruit Juice on the Pharmacokinetics of Tadalafil in Rats. BioMed research international, 2020, 1631735. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7003282/
  14. Hatzimouratidis K. (2014). A review of the use of tadalafil in the treatment of benign prostatic hyperplasia in men with and without erectile dysfunction. Therapeutic advances in urology, 6(4), 135–147. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4054509/
  15. Jackson, G., Arver, S., Banks, I., & Stecher, V. J. (2010). Counterfeit phosphodiesterase type 5 inhibitors pose significant safety risks. International journal of clinical practice, 64(4), 497–504. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3069491/
  16. Tainted Sexual Enhancement and Energy Products. (n.d.) https://www.fda.gov/drugs/medication-health-fraud/tainted-sexual-enhancement-and-energy-products
Editorial Standards

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references. See a mistake? Let us know at [email protected]!

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.

Mike Bohl, MD

Dr. Mike Bohl is a licensed physician and the Director of Scientific & Medical Content at a stealth biotech startup. Prior to joining Hims & Hers, Dr. Bohl spent several years in digital health focusing on patient education. He has also worked in medical journalism for The Dr. Oz Show and Sharecare and has served on the Medical Expert Board of Eat This, Not That!.

Dr. Bohl obtained his Bachelor of Arts and Doctor of Medicine from Brown University, his Master of Public Health from Columbia University, and his Master of Liberal Arts in Extension Studies—Journalism from Harvard University. He is currently pursuing a Master of Business Administration and Master of Science in Healthcare Leadership at Cornell University. Dr. Bohl trained in internal medicine with a focus on community health at NYU Langone Health.

Dr. Bohl is Certified in Public Health by the National Board of Public Health Examiners, Medical Writer Certified by the American Medical Writers Association, a certified Editor in the Life Sciences by the Board of Editors in the Life Sciences, a Certified Personal Trainer and Certified Nutrition Coach by the National Academy of Sports Medicine, and a Board Certified Medical Affairs Specialist by the Accreditation Council for Medical Affairs.

In addition to his written work, Dr. Bohl has experience creating medical segments for radio and producing patient education videos. You can find Dr. Bohl on LinkedIn for more information

Dr. Bohl lives in Manhattan and enjoys biking, resistance training, sailing, scuba diving, skiing, tennis, and traveling. You can find Dr. Bohl on LinkedIn for more information.

Education

  • Bachelor of Arts, Egyptian and Ancient Western Asian Archaeology. Brown University |

  • Doctor of Medicine. |

  • Master of Public Health, General Public Health. |

  • Master of Liberal Arts, Journalism. |

  • Master of Business Administration. | (anticipated 2024)

  • Master of Science, Healthcare Leadership. | (anticipated 2024)

Training

  • NYU Internal Medicine Residency—Brooklyn Community Health Track. |

Certifications

  • Certified in Public Health.

  • Medical Writer Certified.

  • Editor in the Life Sciences.

  • Certified Personal Trainer.

  • Certified Nutrition Coach.

  • Board Certified Medical Affairs Specialist. Accreditation Council for Medical Affairs

  • Digital Storytelling Graduate Certificate.

  • Marketing Management and Digital Strategy Graduate Certificate.

Publications

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