Oral Medications for Erectile Dysfunction: Viagra, Cialis, and Levitra Compared


Oral medications are the most common treatment for erectile dysfunction.  They are sometimes used in combination with other treatments.  Oral medications alone are effective for 60-70% of men suffering from ED.

It’s important to understand that these medications do not cure ED.  However, they allow many men with ED to achieve and maintain an erection.

PDE5 Inhibitors

The major oral medications for ED all operate on the same principle.  They inhibit the action of type 5 phosphodiesterase (PDE5), thereby increasing the blood flow and helping to trap the blood in the penis.  (See our article “How Do Erections Work“).

Side Affects

Side effects of these drugs may include a headache.  You can use over-the-counter pain medications to deal with this.

Less common side effects include nausea, indigestion, nasal congestion, dizziness, and blurred vision.  If you experience side effects, you should talk to your doctor.

There are some variations in how each medication works, so if one doesn’t work, it’s worth trying others.

Viagra (sildenafil)

Viagra is the oldest pde5 inhibitor on the market, so it is very well understood by doctors.

It takes effect in about 30 minutes; for most men the effects last 2-3 hours.  Viagra should not be taken with alcohol, or after eating (especially fatty foods), which can interfere with its effects.

Generics.  The patent on Viaga has expired, so it is available in the US and Canada as a generic (sildenafil citrate), which is considerably less expensive.  The generic form has the same chemical properties as the brand name drug.

Levitra (vardenafil)

Levitra is very similar in its effects to Viagra.  It is less affected by alcohol and food consumption.  There is some evidence that Levitra is more effective for men with diabetes.

Generics.   Levitra is not currently available as a generic.

Cialis (tadalafil)

Cialis can last up to 36 hours, so many men prefer it over Viagra or Levitra.  However, side effects (if any) will also last longer.  Cialis is affected by alcohol, but it is less susceptible to food consumption than Viagra.

Generics.   Cialis is available in generic form (tadalafil) in Canada.  It will be available n the Uniter States in after October 2018, when the final patents expire.

Stendra (avanafil)

Similar to other ode5 inhibitors; may be taken with food,

Generics.   Stendra is not currently available as a generic.

How to Buy

Pde5 inhibitors must be prescribed by a doctor.  The doctor will:

  • determine the likely cause of your erectile dysfunction
  • make sure that the medication will not impact pre-existing medical conditions (if any)
  • make sure that the medication will not have negative interactions with other drugs you may be taking
  • recommend the best medication or your needs

Once your doctor has written a prescription, it can be filled at a local pharmacy. Be sure to compare prices! The cost of the same prescription drug can vary by hundreds of dollars at different pharmacies, even within the same town

How to Find a Safe Online Pharmacy

Prescriptions may also be submitted to an online pharmacy, which may offer better prices.  However, there are many fraudulent pharmacies online, which may sell counterfeit drugs.  According to the FDA, 97% of online pharmacies reviewed by the National Association of Boards of Pharmacy are not in compliance with U.S. pharmacy laws and practice standards1.

Many people in the United States now buy prescription drugs from Canadian pharmacies. But bear in mind that many pharmacies that say they are in Canada actually are not.

Avoiding Unsafe or Fraudulent Pharmacies

  1. Check the pharmacy on the FDA BeSafe registry.
  2. Check for logos indicating accreditation by Verified Internet Pharmacy Practice Sites (VIPPS), Accreditation Commission for Health Care (ACHC), or URAC.  Click the logos to make sure they are actually linked to accreditation, and not just copied and pasted on a fraudulent website.
  3. Avoid pharmacies that do not require a prescription.
  4. Do not order from pharmacies outside of the United States.
  5. Do not deal with pharmacies if their prices seem too good to be true.
  6. Do not deal with pharmacies that do not have a licensed pharmacist available to answer your questions, either by phone or online.

Herbal Supplements

Herbal supplements are generally not very effective.  There may be serious risks associated with using herbal supplements.  See our article “Herbal Medications for Erectile Dysfunction.”


  1. How to Buy Medicines Safely From an Online Pharmacy:  https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm048396.htm

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