What Is an Alpha Agonist?

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  • Written By: Mary McMahon
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 10 October 2019
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An alpha agonist is a chemical compound that stimulates alpha-adrenergic receptors. Normally these receptors interact with transmitters like adrenaline and noradrenaline. An alpha agonist can mimic the effect of these compounds and may be used therapeutically for a variety of purposes. Pharmaceutical companies produce a range of these agonists in different classes, including partially selective medications that can focus on specific kinds of receptors, rather than stimulating all of them.

The opposite of an alpha agonist is an alpha antagonist, also known as an alpha blocker. These medications prevent stimulation of these receptors by locking on to them. The body's own supply of compounds like adrenaline cannot stimulate the receptor because it is blocked. Medications in this class are available to treat conditions where a doctor wants to decrease stimulation of the alpha-adrenergic receptors. These medications are related to beta agonists and antagonists, another group of medications that act on the beta-adrenergic receptors of the body.

When patients take alpha agonists, the medications trigger contraction of smooth muscle throughout the body. They are especially active in the blood vessels, particularly the arteries, and have a vasoconstrictive effect. One reason to give this type of compound is shock or low blood pressure. The medication will clamp the blood vessels down to create an increase in the patient's blood pressure. As the patient stabilizes, the doctor can withdraw the medication and the patient should be able to maintain safe blood pressure independently.


Another reason to use an alpha agonist is in the management of glaucoma. The medication can limit the production of fluid in the eye and prevent progressive damage. Anesthesiologists also use these medications in pain management as part of a drug cocktail to address discomfort associated with surgery. Pain management is critical for surgical patients, as untreated pain can prolong healing time and may lead to secondary issues like depression.

Patients on alpha agonist medications can experience some side effects. Some develop headaches because of the vasoconstriction and they may also experience bradycardia, where the heart rate slows down. Some patients also become restless and may develop nausea, vomiting, and discomfort. If a doctor feels such a medication would be appropriate for a patient, she will calculate the dose carefully. In a hospital setting, nurses and other personnel can monitor patients while they are on alpha agonists. If any signs of distress develop, they can intervene to correct the problem.


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