What Are Parasympathomimetics?

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  • Written By: Marlene Garcia
  • Edited By: Daniel Lindley
  • Last Modified Date: 15 September 2019
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Parasympathomimetics define drugs that mirror the action of the parasympathetic nervous system of the brain and spinal column. These medications either stimulate neurotransmitters that release the chemical acetylcholine or inhibit its action. Parasympathomimetics are used to treat glaucoma, depression, asthma, heart conditions, and retention of urine. Some muscle relaxers and diet pills are also classified as parasympathomimetics, along with nasal decongestants and drugs to treat erectile dysfunction.

These medicines act on neurotransmitters that send messages between muscles and nerves, including main receptors controlling the bladder, heart, lungs, and stomach. The parasympathetic nervous system regulates gland and organ functions while the body is at rest. Also called the automatic nervous system, it controls digestion, sexual desire, and the formation of tears, saliva, urine, and feces without conscious awareness.

The parasympathetic nervous system works as a complement to the sympathetic nervous system, which is activated during stress or danger. This part of the nervous system regulates flight-or-fight chemicals and produces physical reactions, such as faster breathing and heart rate, and increased perspiration. This inborn response also sends more blood to large muscles to enable running away.

Parasympathomimetics work specifically on the chemical acetylcholine to block it or activate it. Drugs that mimic acetylcholine, such as bethanechol chlorides, are commonly administered after surgery to promote urination and defecation. Side effects of these medicines include headache, increased saliva and sweat, and low blood pressure. Some patients report stomach pain when taking these parasympathomimetics.


Pilocarpine hydrochlorides also act on the parasympathetic nervous system by increasing the production of tears and saliva. These are used to treat dry eyes and mouth, and in the treatment of glaucoma. These medicines relieve pressure on the eye by allowing fluid to flow freely, but also constrict pupils. Patients using these parasympathomimetics might experience trouble seeing at night. Eye drops or gel might also produce stinging and headache.

Anticholinergic drugs inhibit acetylcholine receptors, reducing the amount of chemical released. Drugs under this class include antihistamines and asthma drugs. They might decrease the amount of mucus and help open bronchial tubes. Side effects of these drugs might include a faster heart rate, dry mouth, constipation, and vision problems.

Other forms of these drugs serve as muscle relaxers or treat high blood pressure and heart conditions, and gastrointestinal disorders from too much acid production. Some drugs might also ease symptom of depression and psychosis. Erectile dysfunction might improve with parasympathomimetics because the parasympathetic nervous system regulates sexual activity.


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