Can a Patient Take Sildenafil and Cialis Together?
No, patients should not take sildenafil (Viagra) and tadalafil (Cialis) together—this combination is explicitly not recommended and potentially dangerous. 1
FDA-Approved Labeling and Safety Warnings
The FDA drug label for tadalafil explicitly states: "The safety and efficacy of combinations of tadalafil and other PDE5 inhibitors or treatments for erectile dysfunction have not been studied. Inform patients not to take tadalafil with other PDE5 inhibitors." 1
Both medications work through the same mechanism (PDE5 inhibition), and combining them increases the risk of severe hypotension and other adverse effects without proven additional benefit. 2
Guideline-Based Recommendations
The American College of Physicians explicitly recommends optimizing the dose of a single PDE5 inhibitor rather than adding a second agent, as combination therapy increases the risk of severe hypotension and other adverse effects without proven additional benefit. 3, 2
Before declaring treatment failure with a single PDE5 inhibitor, ensure an adequate trial consisting of at least 5 separate attempts at maximum tolerated dose (sildenafil 100 mg or tadalafil 20 mg as needed). 3, 2
Why Combining PDE5 Inhibitors Is Problematic
Both sildenafil and tadalafil cause vasodilation through the same pathway, leading to additive blood pressure-lowering effects that can result in dangerous hypotension, particularly when combined with alcohol or other vasodilators. 1, 4
The most common adverse events (headache, flushing, dyspepsia, nasal congestion, back pain, myalgia) would be expected to occur more frequently and severely with combination therapy. 5, 3
There is no evidence that combining two PDE5 inhibitors provides superior efficacy compared to optimizing the dose of a single agent. 3, 2
Proper Management Strategy If Single Agent Fails
If a patient has inadequate response to one PDE5 inhibitor, the appropriate approach is:
First, verify the trial was adequate: Check that the patient used the maximum dose at least 5 times with proper timing (sildenafil 30-60 minutes before sexual activity on empty stomach; tadalafil up to 36 hours before), ensured adequate sexual stimulation, avoided heavy alcohol use, and addressed any relationship issues. 3, 2
Second, switch to a different PDE5 inhibitor (e.g., from sildenafil to tadalafil or vice versa) rather than combining them, as individual patients may respond better to one agent over another. 6, 7
Third, consider combination therapy with non-PDE5 inhibitor treatments such as testosterone replacement (if hypogonadal), psychotherapy, or other adjunctive therapies—not another PDE5 inhibitor. 5, 3
Critical Safety Considerations
Absolute contraindication: Never prescribe any PDE5 inhibitor (including combinations) to patients taking nitrates in any form (oral, sublingual, transdermal, or recreational "poppers"), as this can cause potentially fatal hypotension. 3, 2, 1
If emergency nitrate administration is required, wait 24 hours after sildenafil or 48 hours after tadalafil before giving nitrates under close medical supervision. 3, 2
Limited Research Exception
One small research study (not guideline-endorsed) found that combining tadalafil 5 mg daily with sildenafil 50 mg as needed at the early stage of treatment improved outcomes in patients with severe ED compared to tadalafil alone. 8
However, this approach contradicts FDA labeling, lacks guideline support, and the study had significant limitations including small sample size and short duration. 8
This research finding does not override the explicit FDA warning and guideline recommendations against combining PDE5 inhibitors. 1, 3, 2
Bottom Line for Clinical Practice
The answer is definitively no—do not prescribe sildenafil and tadalafil together. Instead, optimize the dose of a single PDE5 inhibitor, ensure proper use, address modifiable factors (hormonal deficiencies, timing, sexual stimulation), and if truly inadequate, switch to a different PDE5 inhibitor or add non-PDE5 inhibitor adjunctive therapy. 3, 2, 1