How Does Cialis (Tadalafil) Work?

Medically reviewed by Femi Aremu, PharmD

Cialis is a prescription medication containing the active ingredient tadalafil. Cialis belongs to a group of medications known as phosphodiesterase-5 (PDE-5) inhibitors. Healthcare providers commonly prescribe tadalafil to treat erectile dysfunction (ED).

Estimates suggest that 18 million males in the United States struggle with ED, including 18% of males 20 or older. ED often results in low self-esteem or other mental health concerns, highlighting the importance of treating this condition.

PDE5 inhibitors like tadalafil help ED by allowing more blood to flow into the penis. ED only represents one Food and Drug Administration (FDA)-approved use of PDE5 inhibitors, however.

Healthcare providers may also prescribe tadalafil to manage two other health conditions involving insufficient blood flow: pulmonary arterial hypertension (PAH) and benign prostatic hyperplasia (BPH).

Read on to learn more about how tadalafil works, its brand names, its effectiveness for ED and other conditions, potential side effects, and more.

Understanding ED

With ED, the penis cannot get or stay erect long enough for sex. Several things may cause ED.

Most commonly, the natural aging process limits blood flow into the penis.

ED can also develop as a result of underlying health conditions or the medications that treat them, such as:

• Frequent high blood sugar or uncontrolled diabetes

• Hypertension (high blood pressure)

• Heart disease

• High cholesterol

• Obesity

Additionally, certain risk factors increase the risk of ED, such as smoking, lack of exercise, and drug or alcohol use.

ED occurs more frequently in older men. Only 5% of males between the ages of 20 and 39 report ED symptoms, while over 70% of males over 70 report difficulty having or maintaining an erection.

The most commonly prescribed medications to treat ED are PDE5 inhibitors like Cialis (tadalafil) and Viagra (sildenafil).

Understanding PAH and BPH

PDE5 inhibitors also treat other conditions. One of these is PAH. With PAH, high blood pressure develops when a blockage in the arteries within the lung limits normal blood flow.

This leads to shortness of breath when exercising or completing regular daily activities.

BPH occurs when the prostate and the surrounding tissues become enlarged. The enlarged prostate interferes with the normal flow of urine from the bladder and urinary tract, resulting in lower urinary tract symptoms, such as trouble urinating.

Though this growth is not cancerous, prostate cancer and BPH can co-occur.

The FDA approves tadalafil to help manage PAH and BPH. Brand-name versions of the drug approved for PAH include Adcirca.

Tadalafil works for these conditions by promoting muscle relaxation, which improves blood flow in PAH and urinary flow in BPH.

What Is Cialis?

Cialis is a brand-name prescription medication. It belongs to the drug class known as PDE5 inhibitors.

Tadalafil is its active ingredient and is available as a generic drug. The FDA has approved Cialis to treat ED, symptoms of BPH, or combined ED and BPH in males with both conditions. The drug is approved for use in adults.

Cialis may be prescribed once daily to treat ED, BPH, or both. Alternatively, Cialis may be prescribed as an as-needed treatment for ED, to be taken before sexual activity. For this purpose, one dose works for up to 72 hours.

Tadalafil is the active ingredient in several other brand-name medications that treat BPH or PAH.

The list below summarizes the current brand names of tadalafil-containing drugs and what the FDA approves them to treat:

• Cialis: ED, BPH, or both

• Adcirca: PAH

• Tadliq: PAH

• Alyq: PAH

• Entadfi, a combination drug containing tadalafil and finasteride: BPH

Sometimes, a healthcare provider prescribes a medication off-label to treat a condition outside its FDA-approved uses.

Tadalafil is sometimes prescribed off-label to treat ureteral stones (a type of kidney stone) and Raynaud’s syndrome.

How Cialis Works

Tadalafil and other PDE5 inhibitors primarily work by inducing muscle relaxation.

Tadalafil stops the breakdown of a chemical responsible for relaxing muscles. In ED and PAH, the drug targets muscle cells in blood vessels.

When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this effect is referred to as vasodilation.

In BPH, the medication relaxes the urinary tract and bladder muscles, allowing for more effortless urine flow.

How Effective Is Cialis?

Tadalafil has been extensively studied for ED. In trials investigating Cialis, the majority of participants receiving the drug experienced a significant improvement in ED and maintained an erection.

Compared with other PDE5 inhibitors for ED, Cialis is similar in effectiveness to Viagra (sildenafil) and Levitra (vardenafil).

Interestingly, Cialis has been more linked to improved self-esteem and other psychological factors than the other PDE5 medications.

Cialis is also highly effective in reducing the symptoms of BPH. In trials of the drug, individuals taking Cialis saw a significant reduction in the frequency and urgency of urination and improved urine flow.

Cialis was also investigated in combination with finasteride, another BPH medication, in another trial. The results showed the combination to be even more effective than either medication alone.

Dosing Guidelines

Typical Cialis dosages will differ depending on the conditions it's prescribed to treat as well as other factors. Be sure to follow your healthcare provider’s instructions.

The table below summarizes the typical dosages for tadalafil:

Storage and Discarding

Cialis tablets should be stored in a dry place at room temperature (68-77 F).

If you need to dispose of the drug, take Cialis to a pharmacy that disposes of unwanted medications or check with your local community guidelines for medication disposal.

Side Effects and Safety

Tadalafil may cause mild side effects. The side effects may differ depending on your dosage and medical conditions.

Common mild side effects include:

• Headache

• Upset stomach

• Muscle pain

• Flushing

• Stuffy or runny nose

Of these, headache is the most common side effect and typically disappears within a few hours after taking the medication.

If these side effects worsen or do not go away, contact a healthcare professional for advice.

Rarely, tadalafil has been reported to cause more severe side effects, such as:

• Painful, prolonged erection

• Color vision changes

• Reduction or loss of vision

• Reduction or loss of hearing

If you experience any of these side effects, seek medical attention immediately.

When to Avoid Cialis

Tadalafil may not be safe for everyone.

People with the following conditions or factors may have a higher risk of side effects with this drug:

• Heart problems, such as heart failure, arrhythmias, or heart attack

• Low blood pressure or uncontrolled high blood pressure

• History of stroke

• Liver problems

• Kidney problems, including dialysis

• Retinitis pigmentosa, a rare genetic eye condition

• History of severe vision loss

• Stomach ulcers

• Bleeding problems

• Deformed penis shape or Peyronie’s disease

• History of erections lasting more than four hours

• Blood cell problems

Healthcare providers aren’t likely to prescribe tadalafil if you:

• Have had an allergic reaction to tadalafil or another PDE5 inhibitor

• Take a nitrate medication, such as Nitrostat (nitroglycerin)

• Use recreational drugs called alkyl nitrites (“poppers”)

• Take a guanylate cyclase stimulator medication called Adempas (riociguat)

Potential for Interaction

Certain medications interact with tadalafil. Interactions can lead to severe side effects or may cause medications to be less effective treatments.

Before starting tadalafil, tell your provider about your current medications (prescription and over-the-counter [OTC]) and any vitamins or supplements.

Some medications or other substances known to interact with tadalafil include:

• Nitrates, such as Rectiv (nitroglycerin), which may cause a life-threatening drop in blood pressure if combined with tadalafil

• Alpha-blockers (drugs that slow down or block certain types of cell activity), such as Flomax (tamsulosin)

• Medications that treat high blood pressure, such as Norvasc (amlodipine) or Toprol XL (metoprolol succinate)

• The consumption of alcoholic beverages

• Antacids (medications used to treat heartburn and indigestion), such as Mylanta (magnesium)

• Nonsteroidal anti-inflammatory drugs (NSAIDs), such as Aspirin

This is not a complete list of medications that interact with tadalafil. Therefore, talk to a pharmacist or healthcare provider about avoiding or safely managing drug interactions.

Alternative Treatment Options: ED

Many dietary supplements contain herbs that are promoted for sexual health. Common ingredients include ginseng, horny goat weed, L-arginine, and tongkat ali.

Unfortunately, little evidence supports their effectiveness for ED.

However, other non-drug approaches may help, such as sex therapy, which can help resolve any underlying psychological causes of ED.

Penis pumps and ED rings are other non-drug options for short-term assistance with achieving or maintaining erections.

Improvement may also occur with lifestyle changes, such as weight loss or quitting smoking.

Alternative Treatment Options: PAH and BPH

Alternative options for managing PAH are limited. A low-sodium diet is highly recommended for people with PAH because decreasing sodium intake can help manage symptoms.

Some natural products have demonstrated effectiveness in helping BPH symptoms, such as saw palmetto and African cherry.

However, before taking any supplements, talk to a healthcare provider to ensure the supplement is safe for you to take.

Summary

Cialis is an orally administered PDE5 inhibitor medication most well-known for treating ED.

The drug is also prescribed to treat other conditions involving blood flow problems in the lungs and urine flow problems due to an enlarged prostate.

Cialis works by causing muscle relaxation in some body regions, resulting in improved blood and urine flow.

To learn more about ED treatment options, speak with your healthcare provider.

Frequently Asked Questions

For what purposes can females take tadalafil?

The FDA approves tadalafil for use in females to help manage PAH.

The other approved uses—ED and enlarged prostate—only affect the male anatomy.

Could tadalafil affect existing contraception?

No, tadalafil is not known to interact with any form of contraception. Keep in mind that tadalafil does not prevent pregnancy nor protect against sexually transmitted infections.

Does tadalafil shrink the prostate?

No, tadalafil does not shrink the prostate. Instead, it relaxes muscles involved in urine flow.

This helps to relieve the urinary symptoms associated with an enlarged prostate.

Read the original article on Verywell Health.