Can you take sildenafil (Viagra) and tadalafil (Cialis) together?

Combining Sildenafil and Tadalafil for Erectile Dysfunction

Taking sildenafil (Viagra) and tadalafil (Cialis) together is not recommended due to the increased risk of adverse effects without proven additional benefit for erectile dysfunction treatment.

Mechanism and Rationale

Both sildenafil and tadalafil are phosphodiesterase type 5 inhibitors (PDE5i) that work through the same mechanism:

• They inhibit the PDE5 enzyme, increasing cGMP levels in the corpus cavernosum
• This leads to smooth muscle relaxation and increased blood flow to the penis
• The primary difference is their duration of action (sildenafil: 4-6 hours; tadalafil: up to 36 hours)

Evidence Against Combination Therapy

The American College of Physicians clinical practice guideline does not support combining multiple PDE5 inhibitors 1. Key concerns include:

• Increased risk of adverse effects without proportional efficacy benefits
• Potential for additive hypotensive effects
• No high-quality evidence supporting superior outcomes with combination therapy

The American Urological Association (AUA) recommends using a single FDA-approved PDE5i with proper dose titration to maximize efficacy 1. Their guideline emphasizes optimizing the dose of a single agent rather than combining multiple agents.

Safety Concerns with Combination Therapy

Combining sildenafil and tadalafil may lead to:

1. Increased adverse effects: Both medications share similar side effect profiles including:

   • Headache
   • Flushing
   • Dyspepsia
   • Nasal congestion
   • Visual disturbances
   • Myalgia

2. Cardiovascular risks: Potential for additive hypotensive effects, which could be dangerous, especially in patients with:

   • Cardiovascular disease
   • Patients taking antihypertensive medications
   • Those with baseline hypotension

3. Risk of priapism: Prolonged erection lasting more than 4 hours requiring emergency intervention

4. NAION risk: Both medications carry a risk of non-arteritic anterior ischemic optic neuropathy (NAION), with a relative risk of 1.34 for "possible NAION" 2

Alternative Approaches

If one PDE5i is not effective, the AUA recommends:

1. Dose optimization: Ensure the current medication is being taken at the optimal dose before switching 1

   • Sildenafil: 25mg to 100mg
   • Tadalafil: 5mg to 20mg (as needed) or 2.5-5mg (daily)

2. Proper medication use instruction: Many treatment failures are due to incorrect use 1

   • Taking on empty stomach (especially for sildenafil)
   • Ensuring adequate sexual stimulation
   • Allowing sufficient time for onset of action

3. Sequential monotherapy: If one PDE5i fails despite proper use and dosing, try switching to another PDE5i rather than combining them

4. Consider daily tadalafil: Research shows that men who had incomplete responses to as-needed PDE5i therapy may benefit from switching to daily tadalafil 5mg 3

Special Considerations

1. Drug interactions: Both medications interact with:

   • Nitrates (absolute contraindication)
   • Alpha-blockers (use with caution)
   • CYP3A4 inhibitors (may increase PDE5i levels) 4, 5

2. Medical conditions: Caution in patients with:

   • Cardiovascular disease
   • Hepatic or renal impairment
   • History of NAION or retinitis pigmentosa 4

Limited Evidence for Combination

While one small study suggested potential benefit of combining tadalafil 5mg daily with sildenafil 50mg as needed in severe ED 6, this approach:

• Has not been validated in larger trials
• Is not endorsed by major guidelines
• May increase adverse event risk
• Has not been evaluated for long-term safety

Conclusion

For optimal management of erectile dysfunction, focus on optimizing the dose of a single PDE5 inhibitor rather than combining sildenafil and tadalafil. If one medication fails despite proper use and dosing, consider switching to another PDE5i rather than using them in combination.