Erectile Dysfunction Drug Interactions

Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editors: Melissa Conrad Stöppler, MD

The options to treat erectile dysfunction have increased in the past few years with the introduction of medications that can help promote an erection in males. Once thought to be due only to psychological factors, erectile dysfunction may occur because of a variety of medical conditions and in fact, it may be the initial presenting symptom of serious illness such as atherosclerosis and diabetes.

This illness often remains difficult for patients to discuss with their health care practitioners. With the advent of medications that help promote an erection and with increased advertisement of these medications in the media, the opportunity to have these discussions has improved.

In normal physiology, nerve impulses cause dilation of blood vessels in the penis due to sexual stimulation. Two cylindrical tubes, called the corpus cavernosum, that run the length of the penis fill with this increased blood volume and cause the penis to stiffen, straighten, and become erect. When the sexual stimulation is removed or when ejaculation occurs, the extra blood drains from the penis and the erection resolves.

Erectile dysfunction, previously termed impotence, is a failure of excess blood flow to engorge the corpus cavernosum and cause an erection. There are numerous potential causes and risk factors.

Examples of physiological causes of erectile dysfunction include the following:

Erectile dysfunction may also be due to psychological conditions including depression, anxiety, and stress. Often the inability to maintain an erection is due to a combination of conditions.

Fortunately, medications are available that can help increase blood flow to the penis once sexual stimulation has occurred. Sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra) may be prescribed to help with erectile dysfunction. These medications are classified as phosphodiesterase inhibitors and work by relaxing muscles in the penis, causing blood vessels to dilate and allowing increased blood flow, but only after appropriate physical and emotional sexual stimulation.

There are some potential side effects of these medications and it is important that the patient and health care provider discuss their safe use.

  • Because these medications cause blood vessels to dilate, their use with other medications such as nitrates [for example, isosorbide mononitrate (Imdur, Ismo, Monoket), isosorbide dinitrate (Isordil, Titradose, Dilatrate-SR, Isochron), nitroglycerin (Nitrostat, Nitroquick, Nitrolingual, Nitro-Dur, Minitran, Nitro-Bid and others) that cause similar reactions in the body may cause an unsafe drop in blood pressure, leading to lightheadedness and syncope, or passing out.

  • Erectile dysfunction medications should not be taken with blood thinners or anticoagulation medications such as warfarin (Coumadin) and enoxaparin (Lovenox).

  • Alpha-blocker medications, used to control high blood pressure [for example, doxazosin mesylate (Cardura), prazosin (Minipress)] and symptoms of an enlarged prostate tamsulosin (Flomax) can cause a drop in blood pressure; therefore, erectile dysfunction medications should not be used in conjunction with these drugs.