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Difference Between Vasoconstricting and Vasodilating Medications

Medically Reviewed by Dan Brennan, MD on May 16, 2021

Vasoconstricting and vasodilating medications work in different ways. While vasoconstricting medications tighten your blood vessels to raise blood pressure, vasodilating medications dilate or widen them to improve blood flow and lower blood pressure.

These medications are often used to treat different cardiovascular conditions. Read on to learn more about the differences between these two types of medications and what conditions they can treat.

Vasoconstricting Medications

Vasoconstricting medications are sometimes known as life-support drugs because they can rapidly increase your blood pressure when you’re at a critical care unit for breathing difficulties or low blood pressure.

By sending chemical signals to the smooth muscles lining your blood vessels, these medications tell your blood vessels to tighten, leading to increased blood pressure.

Using vasoconstricting medications. In general, these medications are used to treat people in shock. When a person is in shock, or deprived of oxygen, there is a risk of organ injury caused by low oxygen levels. Vasoconstrictors can rapidly raise the blood pressure of a person in shock, saving their organs from damage.

Additionally, these medications can treat sudden bleeding from your digestive tract’s enlarged veins.

Vasoconstricting medications can also treat migraines. While over-the-counter medicines like NSAIDs or acetaminophen can treat mild migraines, prescription vasoconstrictors like triptan can treat severe migraines. 

Examples of vasoconstricting medications. Many vasoconstrictors are hormones that are found in the body. For example, medicines containing dopamine, norepinephrine, and epinephrine are often used in trauma care to raise your blood pressure. 

Side effects of vasoconstricting medications. Side effects of taking vasoconstrictors can include:

  • Irregular heartbeats
  • Dizziness
  • Diarrhea
  • High blood sugar 

‌If used for a long period of time, vasoconstrictors can also give you gallstones.

Precautions when taking vasoconstrictors. You should only take vasoconstrictors if your doctor has prescribed them for you. Like vasodilators, they can have side effects and may affect your health negatively if you’re not taking the right dosage.

Studies have suggested that vasoconstrictors may be harmful if you have pancreatitis, which already causes you to have low blood pressure. 

You are also more likely to develop heatstroke if you take vasoconstrictors, which affects your body’s ability to respond to heat. You should hydrate more often and try to stay out of the sun in hot weather if you take vasoconstrictors.

Vasodilating Medications

Vasodilating medications are the opposite of vasoconstricting medications. Instead of tightening your blood vessels, they widen them, allowing blood to flow more easily. This lowers your blood pressure.

Like vasoconstrictors, vasodilators affect the muscles in the walls of your blood vessels. They keep the muscles from tightening and narrowing by preventing calcium from entering the blood vessel walls. Other vasodilators, like minoxidil and hydralazine, impact the blood vessel walls directly.

Using vasodilating medications. Vasodilators are usually used to lower blood pressure, particularly during emergencies.

They can treat conditions like:

  • Heart failure
  • High blood pressure
  • High blood pressure affecting your lung arteries (pulmonary hypertension)
  • High blood pressure during pregnancy or childbirth (preeclampsia or eclampsia)

They are also used to treat angina and myocardial infarction. Angina is when you have chest pain because there is less blood flowing to your heart. A myocardial infarction, or a heart attack, happens when blood flow to your heart is blocked.

Examples of vasodilating medications. There are many types of vasodilating medications, including:

  • Nitroprusside, which is used mostly in emergencies and is administered through an IV
  • Labetalol, which can treat severe hypertension (high blood pressure) during labor and prevent eclampsia and hemorrhaging
  • Calcium blockers such as nicardipine and clevidipine, which are also used in an IV during emergencies

Viagra, which widens the blood vessels in the penis to treat erectile dysfunction, is also a vasodilator.

Side effects of vasodilators. Vasodilators can have a lot of side effects since they are powerful medications that doctors often only prescribe when other medicines don’t work.

Side effects can include:

You may also have fluid retention, dizziness, and flushing when taking vasodilators.

You should only take vasodilators if your doctor has prescribed them. Talk to your doctor about your medical history and listen to what they have to say about what medicine you should take. Taking vasodilators without a prescription can be dangerous to your health.

Precautions when taking vasodilators. Remember to keep the following in mind when you are taking vasodilators:

  • Avoid driving until you know how taking a vasodilator will affect you. Some people are particularly sensitive to them and will find it hard to drive when their blood pressure gets low since they can get very dizzy.
  • Ask your doctor if you can take vasodilators with medication for erectile dysfunction. Since most medications for erectile dysfunction, like Viagra, are usually also vasodilators, they may make your blood pressure dangerously low, leading to death.
  • Remember to take your blood pressure regularly while taking vasodilators.

How To Take Vasoconstricting and Vasodilating Medications

Many vasoconstricting and vasodilating medications may only be given in the hospital because small amounts can affect your body heavily. Doctors will monitor you closely and keep an eye on your blood pressure and other organ functions.

If necessary, your doctor may prescribe you a vasoconstricting or vasodilating medicine to take on your own. You should pay close attention to when you take the medicine and follow the prescription instructions.

The number of doses and time between doses depends on your condition. If you have any questions, make sure to talk to your doctor.

WebMD Medical Reference

Sources

SOURCES:

Annals of Surgery: “Adverse effect of therapeutic vasoconstrictors in experimental acute pancreatitis.”

Circulation: “Use of Sildenafil (Viagra) in Patients With Cardiovascular Disease.”

Encyclopedia Britannica: “Adrenergic Drug.”

Hypertension: “Side effects of vasodilator therapy.”

London Health Sciences Centre: Critical Care Trauma Centre: "BLOOD PRESSURE SUPPORT."

Mayo Clinic: "Angina," "Heart attack," “Heatstroke,” “Vasodilators.”

Merck Manual: “Migraine.”

MyHealth.Alberta.ca: “Cirrhosis: Vasoconstrictor Medicines for Variceal Bleeding.”

StatPearls: “Vasodilators.”

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