Medically reviewed by Thomas Fischer (Pharmacist). This article was written according to medical standards. More Info

Medically reviewed by Thomas Fischer (Pharmacist)More Info

You probably already know that Viagra is a popular medication for treatment of erectile function. However, you might not know about its potential drug interactions or contraindications. Keep reading to understand how to use this medication as safely as possible.

Interactions between Viagra and Other Drugs

Let your doctor know about any medications or substances you are taking while using Viagra. Remember, this includes all the following types of drugs:

Viagra

If you take any of the following medications, it is especially critical to talk with your doctor:

Patients who take protease inhibitors for HIV should talk with their doctor before using Viagra. Protease inhibitors can cause increased risk and severity of Viagra’s side effects. Because of this, the dosage of Viagra is usually limited to 25mg every 48 hours in such individuals.

Taking alpha-blockers too close to the time Viagra is ingested can lead to dangerously low blood pressure. This can be avoided by taking the alpha-blockers at least four hours before taking Viagra.

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Viagra and Aspirin

Taking Viagra with other medications can sometimes be dangerous. Some lists of interactions do not include non-prescription drugs, even though some do interact with Viagra. One of these is aspirin, often used for pain relief.

Viagra and Aspirin

Aspirin can also be used for mild inflammation or flu symptoms. Since aspirin is an over-the-counter drug, people may take more than the recommended dose. These doses are high enough to cause interactions with Viagra. Aspirin works as a blood thinner. The thinner blood can flow more easily through the blood vessels, thus fighting inflammation. However, it is problematic to use a blood thinner like aspirin with Viagra, since Viagra widens the blood vessels.

Taking Viagra with aspirin can lead to a higher risk of gastrointestinal side effects like nausea and vomiting. The dilation of blood vessels caused by Viagra can also increase the effect of the aspirin. The interaction of the two drugs can also decrease the amount of time Viagra is effective.

Viagra and Grapefruit

Grapefruit and its juice can affect the way Viagra functions. One study showed that 23% more of the erectile dysfunction drug was absorbed when it was taken with grapefruit juice instead of water.  Grapefruit juice contains a substance that sticks to an enzyme in your digestive tract. This affects the absorption of other foods and medications, including Viagra.

Grapefruit juice can delay Viagra’s absorption, leading patients to believe it is not working. If an individual thinks that the medication is not working, he may take a larger dose and even end up overdosing.

It has not yet been proven whether other citrus fruits cause similar problems with Viagra’s absorption. However, you must always follow the instructions that come with any medication, paying close attention to what kinds of interactions may occur with food, drink, or other medicines.

Interaction of Viagra and Alcohol

In general, taking Viagra with alcohol is not a good idea. There can be several undesired effects. First, alcohol use can actually cause erectile dysfunction problems.

The interaction of alcohol with Viagra can also increase the intensity of Viagra’s side effects. This can lead to dizziness, fainting, or heart palpitations. Additionally, alcohol can decrease Viagra’s effectiveness. Viagra works by dilating blood vessels to increase blood flow to the penis, allowing an erection to occur. Alcohol slows bodily functions, including blood flow, thus working against Viagra’s desired effect.

Some men may find they can use Viagra safely and effectively while drinking alcohol in moderation. In general, this means less than three drinks per day and not more than one drink an hour.  While mixing alcohol with Viagra may not immediately result in damage to your health, long-term health risks do exist. Some of these are:

For your safety, consult your doctor before using Viagra with alcohol. He may agree that it is safe for you to drink in moderation if you do not experience extreme side effects. However, remember that this means no more than two drinks per day, spaced more than an hour apart. Each of the following is considered to be a single drink:

Absolute Contraindications to Viagra: When Should I Not Take Viagra?

Certain health conditions can make it dangerous to take Viagra. You should also not take Viagra if you are allergic to sildenafil or take nitrate drugs.

Conditions

If you have any of the following conditions, it can be risky to take Viagra. Be sure to talk to your doctor if you are thinking about taking it and have one of these conditions:

Other Contraindications

Viagra and High Blood Pressure

Since Viagra acts to increase the dilation of blood vessels, it may lower blood pressure. People who are thinking about using medication for erectile dysfunction should consult with their doctor. 

When Can Viagra Be Dangerous?

One of the most dangerous potential side effects of Viagra is damage to the optic nerve — nonarteritic anterior ischemic optic neuropathy (NAION). This side effect is extremely rare, but if it occurs, the damage is irreversible. There are specific anatomical risk factors for NAION that can be identified through an eye exam. Thus, if you are concerned about this possibility, you can have your eye care professional screen you for risk factors.

Other possible side effects include:

Viagra can contribute to hearing loss and vision loss. It is not yet understood how Viagra is linked to vision loss. It is thought that Viagra may decrease blood supply to the optic nerve, which can cause loss of vision. This is very rare and most frequently occurs in patients who have pre-existing problems with their eyes, heart disease, diabetes, high cholesterol, or high blood pressure.

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Precautions and Warnings - Drug interactions

It is crucial to understand what medications are unsafe to take with Viagra. The most dangerous combination is the mixture of Viagra with nitrate drugs. Nitrate drugs are typically used for treating heart problems or chest pain. They include amyl nitrate, isosorbide dinitrate, isosorbide mononitrate, nitroglycerin, and nitrite poppers. Taking Viagra with any of these drugs can cause an immediate and life-threatening drop in blood pressure.

Another medication that cannot be combined with Viagra is Adempas (riociguat). This drug is used for the treatment of pulmonary hypertension.

Pre-existing conditions

If you are thinking about using Viagra, it is crucial for your doctor to know if you have had any of these conditions:

Let your doctor know if you have ever experienced an erection that lasted hours. Include information about whether you have recently been dehydrated or if you smoke. Tell your healthcare provider if you have been told not to have sexual intercourse due to health problems.

Vision loss and other side effects

As explained above, Viagra has been linked to sudden vision loss in rare cases. Risk factors for this side effect include:

If you notice a sudden loss of vision, stop using Viagra immediately. Get emergency medical help as soon as possible.

Get in contact with your doctor right away if you have any of the following symptoms during sexual activity while taking Viagra:

Age restrictions

Viagra is approved for use by individuals 18 years of age and older. In general, it should not be administered to anyone below this age.

Surgery

Before you have any surgical work done, let your doctor or surgeon know you are taking Viagra. This includes dental procedures.

Driving and Operating Machinery

Some men experience dizziness when using Viagra. As explained earlier, there can also be side effects involving vision. You need to be aware of how your body reacts to this medication before you drive or operate machinery.

Viagra During Pregnancy and Breastfeeding

The FDA has only approved Viagra for use by men, so it usually would not be an issue for women during pregnancy or outside of it. However, sildenafil could be prescribed for a woman with other conditions, such as pulmonary arterial hypertension.

Please consult your doctor if you are thinking about becoming pregnant while using sildenafil. It is not known whether sildenafil passes into breast milk. Talk with your doctor about whether it is safe to breastfeed while taking sildenafil.

You should never take medications without consulting your doctor. This is even more critical during pregnancy and breastfeeding due to the potential effects on the baby.

References:
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