Cialis: Usage, Dosage, Interactions, Side Effects & More

Cialis® (tadalafil) is a medication that’s used to treat erectile dysfunction (ED). Similar to drugs like Viagra® (sildenafil) and Levitra® (vardenafil), Cialis makes it easier to get and maintain an erection when you feel sexually aroused.

Tadalafil, the active ingredient in Cialis, was developed in the early 2000s and approved by the FDA as a treatment for erectile dysfunction in 2003, making it slightly newer than medications like Viagra. 

Cialis is a prescription medication that’s used to treat erectile dysfunction. Like Viagra and other medications used to treat erectile dysfunction, it belongs to a class of medications referred to as PDE5 inhibitors.

PDE5 inhibitors work by inhibiting the action of cGMP-specific phosphodiesterase type 5 — an enzyme that’s responsible for regulating blood flow into and out of the soft erectile tissue of the penis.

What Is Cialis (Tadalafil) Used For?

Aside from being known as a popular ED treatment, Cialis is also widely known for its long duration of action. A single Cialis tablet can last for as long as 36 hours, making it much longer lasting than other ED medications. 

Healthy erections are all about blood flow. When you feel sexually aroused, blood flows to your corpora cavernosa — the soft, sponge-like tissue of your penis — causing it to become firm and enlarged. 

By inhibiting the effects of the PDE5 enzyme, Cialis helps blood to flow into the erectile tissue of your penis, making it easier for you to get and stay hard. 

However, tadalafil — the active ingredient in Cialis — isn’t only used to treat erectile dysfunction. It’s also prescribed to treat the following conditions:

Cialis for Benign Prostatic Hypertrophy (BPH)

Widely known as prostate enlargement, BPH is a condition that causes growth of the prostate gland. It’s common in older men and can cause irritating symptoms, such as difficulty urinating and urinary tract infection.

Cialis, typically in a reduced dosage, once-per-day version, is approved by the FDA as a treatment for BPH.

Cialis for Pulmonary Arterial Hypertension (PAH)

PAH is a rare lung disorder that causes high blood pressure in the lungs without any clear reason.

Tadalafil, the active ingredient in Cialis, is approved as a treatment for people with PAH to improve exercise and prevent the disorder from worsening. When used for PAH, this medication may be sold under the brand name Adcirca®.

Cialis (Tadalafil) Dosages

Cialis is available in several different dosages. When Cialis is prescribed for use as needed, it comes in three dosages:

• 10mg. This is the recommended starting dosage of Cialis for erectile dysfunction, taken as needed before sexual activity.

• 20mg. This is the maximum dosage of Cialis for erectile dysfunction. It’s typically used if the 10mg starting dosage of Cialis isn’t effective.

• 5mg. Cialis may be prescribed at a dosage of 5mg. This lower dosage of Cialis may be used if the 10mg starting dosage produces too many side effects, or if a person only has mild ED and may benefit from a reduced dosage.

Cialis Daily Dosage

Cialis is also available as a daily-use medication. When prescribed for daily use, Cialis comes in two dosages — 5mg or 2.5mg per tablet.

There’s no ideal dosage of Cialis for everyone. Your healthcare provider may adjust your Cialis dosage based on your overall health, the severity of your ED, the frequency and severity of any side effects you experience and a range of other factors.

Missed Dose Instructions

If you’re prescribed Cialis for daily use, it’s not unreasonable to assume you might miss a dose every once in a while. 

If this happens and you do forget to take your daily Cialis dose, take it as soon as you remember. 

However, if it’s almost time to take your next dose, skip your missed dose and go back to your regular dosing schedule. 

Cialis (Tadalafil) Side Effects

When used as prescribed, Cialis is a safe, effective medication for most people. However, like other medications, it can cause side effects. Most side effects of Cialis are mild and temporary, although it may also cause several uncommon, more severe side effects.

The side effects of Cialis are similar to those of other erectile dysfunction medications, such as Viagra (sildenafil), Levitra (vardenafil) and Stendra® (avanafil). 

Common Side Effects

• Headache. Like other ED medications, Cialis may cause headaches. In clinical trials of Cialis, between 11 percent and 15 percent of people experienced headaches, depending on the dosage of medication they used.

• Dyspepsia (indigestion). Dyspepsia, or indigestion, is a common side effect of Cialis and other ED medications. Between four percent and 10 percent of people who used Cialis in clinical trials reported this side effect.

• Back pain. A small percentage of people who use Cialis — from three percent to six percent in clinical trials, depending on dosage — may experience back pain.

• Myalgia (muscle pain). Myalgia, or muscle pain, is a potential side effect of Cialis that affects a small percentage of users. In clinical trials, this side effect was reported by one to four percent of people who used Cialis.

• Nasal congestion. Approximately two to three percent of people given Cialis in clinical trials reported nasal congestion. This is a relatively common side effect of ED medications, such as Viagra and Levitra.

• Flushing. Another potential side effect of ED medications, approximately two to three percent of people who used Cialis in trials reported experiencing flushing (involuntary, temporary reddening of the skin) of the face and body.

• Pain in limbs. Between one and three percent of people who used Cialis in clinical trials reported pain in the limbs.

Note that the statistics provided above are for Cialis used as needed at a dosage of either 5mg, 10mg or 20mg. When taken daily at a lower dosage, many of the common side effects of Cialis occur less frequently.

Like other PDE5 inhibitors, Cialis may cause a mild drop in your blood pressure levels if used with other common medications. It is important to inform your healthcare provider of all the medications and supplements you take regularly. .

Rare Side Effects

Although uncommon, Cialis may cause serious side effects. Contact your healthcare provider or seek medical assistance immediately if you experience any of the following symptoms:

• Blurred vision
• Changes in your perception of color (such as difficulty differentiating between blue and green or seeing a blue tint)
• Chest pain
• Difficulty breathing
• Difficulty swallowing
• Dizziness
• Hives
• Rash
• Ringing in your ears
• Skin peeling or blistering
• Sudden loss of hearing, or reduced hearing
• Sudden loss of vision, or reduced vision
• Swelling of your face, throat and mouth, tongue, lips or other parts of your body
• Erection that lasts longer than four hours 

Like other ED medications, there have been rare reports of priapism — painful erections that can last for several hours — in men who use Cialis. Priapism is a highly uncommon side effect that requires urgent medical attention.

If, after using Cialis, you develop a persistent and/or painful erection that lasts for four hours or longer, seek emergency medical assistance.

Cialis (Tadalafil) Drug Interactions

Cialis may interact with other medications. While some drug interactions that involve Cialis are mild, others can cause serious, potentially life-threatening side effects. 

Cialis and generic tadalafil can interact with several medications used to treat heart conditions and hypertension (high blood pressure). In particular, Cialis can interact with nitrates and alpha blockers used to lower blood pressure.

Cialis should not be used with nitrates, such as nitroglycerin and other nitrates used to manage hypertension. When used together, these medications may cause a sudden, significant drop in blood pressure that could lead to fainting, heart attack or stroke.

If you’re prescribed an alpha blocker or other antihypertensive medication, it’s essential that you inform your healthcare provider before using Cialis.

Some other medications may affect your body’s absorption of Cialis, resulting in higher or lower levels of exposure to the medication. Specifically, medications that inhibit the CYP3A4 enzyme, such as ketoconazole (an antifungal medication) and ritonavir (an antiretroviral medication used in the treatment of HIV/AIDS), may increase Cialis exposure and effectiveness.

Medications that induce the CYP3A4 enzyme, such as rifampicin, may reduce Cialis exposure and effectiveness.

Finally, grapefruit juice may affect the body’s metabolism of Cialis and cause an increased risk of side effects.

To avoid drug interactions, make sure to tell your healthcare provider about all medications that you currently use, both over-the-counter and prescription, before discussing Cialis.

The Bottom Line on Cialis

Cialis is one of the most popular and clinically effective FDA-approved ED treatments on the market. It belongs to a class of medications called PDE5 inhibitors.

Its main ingredient, tadalafil, is also approved by the FDA to treat BPH and PAH.

While Cialis is considered safe for most people, there are, like most prescription medications, some potential side effects that might not make it the right choice for everyone — especially if you take nitrates, alpha blockers and other medications used to treat high blood pressure. You can find out more about Cialis' various side effects in our complete guide to Cialis side effects.

Cialis is typically used by people who are looking for prolonged periods of sexual activeness, because it can work for as long as 36 hours — much longer than other ED medications like Viagra or Levitra, which are designed for use as-needed. 

If you want to learn more about what else is out there, also be sure to check out our guide to ED treatment options.

And of course, always talk to your healthcare provider if you have any questions about using Cialis safety, or whether or not you should consider another treatment for the ED symptoms you're experiencing.