Tadalafil vs Sildenafil (ED Medications)

Nursing Knowledge

Tadalafil vs Sildenafil (ED Medications)

Erectile dysfunction affects millions of people worldwide, significantly impacting quality of life and interpersonal relationships. Pharmacological treatments primarily include phosphodiesterase inhibitors like sildenafil and tadalafil. Keep reading for nursing client education points, side effects and precautions, and a comparison of the most common medications.
Last updated: December 4, 2023

Table of contents

What is erectile dysfunction? 

Erectile dysfunction (ED) is the inability to achieve or maintain an erection sufficient for sexual intercourse.

Risk factors for ED include: 

  • Age > 40 years
  • Chronic disease
  • Certain medications
  • Psychological distress

Clinical tip: Erectile dysfunction can be an early warning sign of a wide range of serious conditions, including cardiovascular disease and diabetes. Clients who report erectile dysfunction should be screened for underlying pathology.

Pharmacological treatment of erectile dysfunction

Erectile dysfunction is treatable with phosphodiesterase inhibitors: 

  • Sildenafil (Viagra)
  • Vardenafil (Levitra) 
  • Tadalafil (Cialis) 
  • Avanafil (Stendra) 

All of those medications are administered orally and are typically taken 15–60 minutes before sexual activity. Tadalafil can be taken daily. 

Phosphodiesterase inhibitors: mechanism of action

Cyclic GMP (cGMP) is an enzyme that regulates ion channel conduction in smooth muscle, causing vasodilation. Phosphodiesterase 5 (PDE5) is an enzyme that breaks down cGMP, leading to vasoconstriction.

PDE5 inhibitors block PDE5 function, which prevents the breakdown of cGMP. Higher cGMP levels increase vasodilation. Increased vasodilation facilitates penile engorgement and sustained erectile function.

Side effects of Viagra, Levitra, Cialis, and Stendra 

Common side effects occurring with ED drugs include: 

  • Headache
  • Flushing
  • Upset stomach
  • Worsening sleep apnea
  • Hypotension 


  • Coronary heart disease
  • CV event in previous 6 months (MI, stroke, serious dysrhythmia) 
  • Preexisting low or high BP
  • Heart failure
  • Unstable angina 

Client education about ED medications

  • Never combine PDE5 inhibitors and nitroglycerine. Can be fatal! 
  • Caution when combining PDE5 inhibitors and other vasodilators due to hypotension risk.
  • Priapism is a painful erection; seek medical intervention if priapism lasts > 4 hours. Can cause permanent damage.
  • Avoid grapefruit and large, fatty meals, which can delay onset of medication.

Tadalafil vs sildenafil vs vardenafil vs avanafil

Table: Comparison of erectile dysfunction drugs 

Sildenafil (Viagra)Tadalafil (Cialis)Vardenafil (Levitra)Avanafil (Stendra)
Onset30–60 minutes30–45 minutes (sometimes sooner)30–60 minutesQuickest; 15–30 minutes
Duration of action4–6 hoursUp to 36 hours4–6 hours6–12 hours
Food interactionsHigh-fat meal can slow absorption.Not significantly impactedHigh-fat meal can slow absorption.Not significantly impacted

A notable difference between the well-known drugs sildenafil (Viagra) and tadalafil (Cialis) is the duration of action: While sildenafil works for about 4–6 hours, tadalafil can have an effect for up to 36 hours, allowing for more spontaneity and earning the  medication the nickname “weekend pill.” 


Tadalafil vs Sildenafil (ED Medications)

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Definition of erectile dysfunction, risk factors, pharmacological treatment, and client education.

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