Oral medications are often the first line of treatment for erectile dysfunction. For most men who have trouble keeping an erection firm enough for sex (erectile dysfunction), these medications work well and cause few side effects.

Sildenafil (Viagra), vardenafil (Levitra, Staxyn), tadalafil (Cialis) and avanafil (Stendra) are oral medications that reverse erectile dysfunction by enhancing the effects of nitric oxide, a natural chemical your body produces that relaxes muscles in the penis. This increases blood flow and allows you to get an erection in response to sexual stimulation.

How oral medications differ

Although they work in similar ways, each oral medication has a slightly different chemical makeup. These minor differences affect the way each medication works, such as how quickly it takes effect and wears off, and the potential side effects. Your doctor will consider these factors as well as other conditions you have and possible interactions with other medications you take.

• Sildenafil (Viagra). This medication is most effective when taken on an empty stomach one hour before sex. It's effective for four to five hours or more if you have mild to moderate erectile dysfunction.

• Vardenafil (Levitra, Staxyn). This medication also is most effective when taken one hour before sex and can be taken with or without food. A high-fat meal might keep it from absorbing as quickly.

  Vardenafil is effective for four to five hours or more if you have mild to moderate erectile dysfunction. A newer form of the drug that dissolves on the tongue might work faster than the pill that you swallow.

• Tadalafil (Cialis). This medication is taken with or without food about one to two hours before sex. It's effective for up to 36 hours. It can be taken in a small dose daily or in a larger dose as needed.
• Avanafil (Stendra). This medication is taken with or without food 30 minutes before sex, depending on the dose. It lasts up to six hours.

Because these drugs are similarly effective, the American College of Physicians recommends that the choice be based on your preferences, including cost, ease of use, how long the drug's effects last and side effects. There are generic versions of sildenafil, verdenafil and tadalafil available.

When oral medications might not be safe

Before taking any medication for erectile dysfunction, get your doctor's OK. Medications for erectile dysfunction might not work or might be dangerous if you:

• Take nitrate drugs — commonly prescribed for chest pain (angina) — such as nitroglycerin (Nitro-Dur, Nitrostat, others), isosorbide mononitrate (Monoket) and isosorbide dinitrate (Dilatrate-SR, Isordil)
• Have very low blood pressure (hypotension) or uncontrolled high blood pressure (hypertension)
• Have severe liver disease
• Have kidney disease that requires dialysis

Side effects

Most men who take oral erectile dysfunction medications aren't bothered by side effects. When side effects do occur, they can include:

• Flushing
• Headache
• Indigestion
• Visual changes, such as blue tinge to vision, sensitivity to light or blurred vision
• Stuffy or runny nose
• Back pain

Rarely, more-serious side effects can occur, including:

• Hearing loss or vision loss. Some men have had sudden loss of hearing or loss of vision after taking one of these medications. However, it isn't clear whether vision or hearing loss was directly caused by taking the medication or by a preexisting condition. If you're taking an oral erectile dysfunction medication and have sudden loss of hearing or vision, seek prompt medical attention.
• An erection that doesn't go away on its own. Called priapism, this rare condition can be painful and requires medical treatment to avoid damage to your penis. If you have an erection that lasts more than four hours, seek immediate medical attention.

Buying oral erectile dysfunction medications online

Treatments for erectile dysfunction are big business, and online scams abound. If you do buy medications over the internet:

• Check to see if an online pharmacy is legitimate. Never order medications from an online pharmacy if there's no way to contact the pharmacy by phone, if prices seem too good to be true or if you're told no prescription is necessary. Some illegal businesses sell counterfeit versions of legitimate medications, which can be ineffective or dangerous. In the U.S., the National Association of Boards of Pharmacy can tell you whether an online pharmacy is licensed and in good standing.
• Make sure you get the right prescription and dose. When you order medications — and when you receive them in the mail — make sure they're the exact dose and type prescribed by your doctor.
• Don't be fooled into buying 'herbal viagra.' Never take any medications that claim to be the "herbal" or nonprescription equivalent of an oral medication for erectile dysfunction. These aren't an effective alternative, and some contain harmful substances.

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June 11, 2019 See more In-depth