Cialis Drug Interactions: A Complete Guide

Cialis (Tadalafil) is generally safe and effective when used as prescribed. But like most medications, it can interact with other drugs, supplements, and even certain foods in ways that range from mildly inconvenient to genuinely dangerous.

This guide covers the major and moderate drug interactions for Cialis — based on FDA labeling and clinical evidence — so you know what to avoid and what to discuss with your doctor.

How Drug Interactions Work With Cialis

Cialis lowers blood pressure by relaxing blood vessel walls. That's how it works for ED, BPH, and pulmonary hypertension. Most of its dangerous interactions involve other substances that also lower blood pressure — stacking these effects can cause a dangerous drop.

Cialis is also processed by a liver enzyme called CYP3A4. Medications that inhibit this enzyme can increase Tadalafil levels in your blood (raising the risk of side effects), while medications that activate this enzyme can decrease Tadalafil levels (reducing its effectiveness).

Medications That Interact With Cialis

Dangerous (Contraindicated) Interactions

These combinations should never be used with Cialis:

• Nitrates — This is the most dangerous interaction. Nitrate medications include:
  • Nitroglycerin (Nitrostat, Nitro-Dur, Nitro-Bid)
  • Isosorbide Dinitrate (Isordil, Dilatrate)
  • Isosorbide Mononitrate (Imdur, Monoket)
  • Amyl nitrite ("poppers" — recreational inhalants)

  Combining Cialis with any nitrate can cause a severe, potentially fatal drop in blood pressure. If you take nitrates for chest pain or heart disease, Cialis is not an option. Tell your doctor about all nitrate use, including recreational poppers.

• Riociguat (Adempas) — A medication for pulmonary hypertension. Like nitrates, combining it with Cialis causes dangerous hypotension. This combination is contraindicated.
• Other PDE5 inhibitors — Do not take Cialis with Sildenafil (Viagra), Vardenafil (Levitra), or Avanafil (Stendra). Also do not combine Cialis with Adcirca, Alyq, or Tadliq — these all contain the same active ingredient, Tadalafil.

Major Interactions (Use With Caution)

• Alpha-blockers — Medications like Tamsulosin (Flomax), Doxazosin (Cardura), Alfuzosin (Uroxatral), and Terazosin are used for BPH or high blood pressure. Combined with Cialis, they can cause additive blood pressure lowering, leading to dizziness, lightheadedness, or fainting.

  What to do: If you need both, your doctor should start Cialis at the lowest dose (5 mg or less) only after you're stable on your alpha-blocker. Take them at different times of day if possible.

• Strong CYP3A4 inhibitors — These medications slow down how your body processes Cialis, increasing Tadalafil levels and the risk of side effects:
  • Ketoconazole (Nizoral) — antifungal
  • Itraconazole (Sporanox) — antifungal
  • Ritonavir (Norvir) — HIV protease inhibitor
  • Clarithromycin (Biaxin) — antibiotic

  What to do: Your doctor may reduce your Cialis dose. For example, with Ritonavir, the maximum as-needed dose is typically limited to 10 mg every 72 hours.

Moderate Interactions

• Blood pressure medications — Antihypertensives like Amlodipine (Norvasc), Lisinopril (Zestril/Prinivil), and Metoprolol (Lopressor/Toprol-XL) can add to Cialis's blood-pressure-lowering effect. This doesn't mean you can't take them together — many men safely do — but your doctor should monitor for excessive drops, especially when starting Cialis.
• Moderate CYP3A4 inhibitors — Medications like Erythromycin, Fluconazole (Diflucan), and Diltiazem (Cardizem) can moderately increase Tadalafil levels. Your doctor may monitor for side effects but usually won't need to adjust the dose significantly.
• CYP3A4 inducers — These speed up Cialis metabolism, potentially making it less effective:
  • Rifampin (Rifadin) — tuberculosis treatment
  • Carbamazepine (Tegretol) — seizure medication
  • Phenytoin (Dilantin) — seizure medication

  What to do: Your doctor may need to increase your Cialis dose or consider an alternative approach.

Supplements and Over-the-Counter Medications to Watch

Drug interactions aren't limited to prescription medications. Watch out for:

• Herbal ED supplements — Products marketed as "natural" ED remedies sometimes contain undeclared PDE5 inhibitors or ingredients that interact with Cialis. The FDA has issued warnings about numerous supplements contaminated with hidden drug ingredients. Don't combine unregulated ED supplements with Cialis.
• Blood pressure supplements — Garlic supplements, CoQ10, and fish oil in high doses can have mild blood-pressure-lowering effects. While not dangerous on their own, combined with Cialis and prescription antihypertensives, they could contribute to excessive drops.
• St. John's Wort — This herbal supplement is a CYP3A4 inducer, meaning it can reduce Tadalafil levels and make Cialis less effective.
• OTC pain relievers — NSAIDs like Ibuprofen (Advil) and Naproxen (Aleve) are generally fine with Cialis, but if you're on blood thinners or have kidney issues, check with your doctor.

Food and Drink Interactions

• Grapefruit and grapefruit juice — Grapefruit inhibits CYP3A4, which can increase Tadalafil levels in your blood. While a small amount is unlikely to cause problems, regular or large quantities of grapefruit could raise the risk of side effects like headache, flushing, and dizziness. Consider avoiding it or limiting intake.
• Alcohol — Excessive alcohol (more than a drink or two) combined with Cialis increases the risk of low blood pressure, dizziness, and headache. Moderate alcohol use is generally fine, but heavy drinking can also worsen ED — which defeats the purpose.

What to Tell Your Doctor

Before starting Cialis, make sure your doctor knows about:

1. All prescription medications — Especially nitrates, blood pressure drugs, alpha-blockers, HIV medications, and antifungals.
2. All over-the-counter medications — Including pain relievers, antacids, and allergy medications.
3. All supplements and herbal products — Including vitamins, herbal ED remedies, and St. John's Wort.
4. Recreational substances — Especially poppers (amyl nitrite), which are contraindicated with Cialis.
5. Your complete medical history — Heart disease, stroke history, low blood pressure, liver or kidney problems, eye conditions (especially NAION), and blood cell disorders like sickle cell anemia.

Don't be embarrassed or skip anything. Your doctor needs the full picture to prescribe safely.

For more on side effects to monitor, see our Cialis side effects guide. And for general information about the medication, check out What Is Cialis?

Final Thoughts

Most Cialis drug interactions are manageable — your doctor can adjust doses or timing to keep you safe. The one absolute rule: never combine Cialis with nitrates or Riociguat. That interaction is dangerous and potentially fatal.

For everything else, honest communication with your doctor is the key. Bring a list of every medication, supplement, and substance you use, and let them make the call on what's safe.

Ready to fill your prescription? Medfinder can help you find Cialis in stock at a pharmacy near you.