How Both Work
Both drugs block the PDE5 enzyme. The key differences are how long each drug stays active and which other PDE subtypes they incidentally inhibit — which explains their distinct side-effect profiles.
Side-by-Side Comparison
| Feature | Viagra · sildenafil | Cialis · tadalafil |
|---|---|---|
| Drug class | PDE5 inhibitor | PDE5 inhibitor |
| Active ingredient | sildenafil citrate | tadalafil |
| Available strengths | 25 mg · 50 mg · 100 mg | 2.5 mg · 5 mg · 10 mg · 20 mg |
| Typical onset | 30–60 minutes | Up to 2 hours |
| Duration | 4–6 hours | 24–36 hours the weekend pill |
| Daily use option | No as-needed only | Yes 2.5 mg · 5 mg |
| BPH approved | No | Yes tadalafil |
| PAH approved | Yes Revatio | No |
| Generic available | Yes widely available | Yes widely available |
| Food interaction | High-fat meals delay onset | Not significantly affected |
| Unique PDE cross | PDE6 → visual side effects | PDE11 → back/muscle aches |
Side Effects
Common to both
- Headache
- Facial flushing
- Nasal congestion
- Dyspepsia (indigestion)
- Dizziness
Viagra-specific
- Visual disturbances — blue-tint or altered color perception
- Increased light sensitivity
- Blurred vision
Due to incidental PDE6 inhibition in retinal cells
Cialis-specific
- Back pain
- Muscle aches (myalgia)
Attributed to PDE11 inhibition in skeletal muscle
Important Safety Information
Nitrate medications: Both sildenafil and tadalafil are contraindicated with any nitrate drug (nitroglycerin, isosorbide mononitrate, isosorbide dinitrate, amyl nitrite). Combining them can cause a sudden, severe drop in blood pressure that can be life-threatening.
Alpha-blockers: Concurrent use requires caution. Blood pressure-lowering effects may be additive. Your prescriber will determine if the combination is appropriate and advise on timing.
This is not a complete safety profile. Always review prescribing information and discuss your full medication list with your healthcare provider.
Brand Pill Imprints
Generic sildenafil imprints vary widely by manufacturer.
Generic tadalafil imprints vary widely by manufacturer.
Frequently Asked Questions
Which works faster — Cialis or Viagra?
Viagra (sildenafil) is faster. It typically takes effect in 30–60 minutes. Tadalafil (Cialis) can take up to 2 hours to reach full effect, though some people notice effects sooner. If the speed of onset matters most, sildenafil has the edge.
Which lasts longer — Cialis or Viagra?
Cialis (tadalafil) lasts significantly longer — up to 24–36 hours, which earned it the nickname "the weekend pill." Viagra's effects typically last 4–6 hours. For couples who prefer more flexibility around timing, tadalafil's longer window is the distinguishing factor.
Can either medication be taken every day?
Tadalafil (Cialis) has an FDA-approved daily option at lower strengths (2.5 mg and 5 mg). This formulation is designed for continuous, once-daily use and also carries approval for benign prostatic hyperplasia (BPH), making it useful for men managing both conditions simultaneously. Sildenafil (Viagra) is taken as-needed and is not approved for daily use at its ED-approved strengths.
Are these medications safe with blood pressure drugs?
Both are contraindicated with nitrate medications (such as nitroglycerin or isosorbide). The combination can cause a severe, potentially life-threatening drop in blood pressure. Caution is also required with alpha-blockers. Neither medication should be combined with any cardiovascular drug without explicit guidance from your prescriber — bring your full medication list to any consultation.
Which is cheaper — generic sildenafil or generic tadalafil?
Both are available as generics and are considerably less expensive than their brand-name versions. Generic sildenafil has been available longer and is often the most affordable option at many pharmacies. Generic tadalafil has also become widely available and is competitive in price. Actual cost varies by pharmacy, insurance coverage, and coupon programs. Brand-name Viagra and Cialis are substantially more expensive than either generic.