Anticholinergic effects are a range of side effects caused by medications that interfere with a specific chemical messenger in the body. Many common drugs produce these effects, even if it is not the medication’s primary purpose. These side effects can influence various bodily functions, from causing a dry mouth to affecting concentration. Understanding what these effects are and which medications cause them is a step toward managing them effectively.
The Role of Acetylcholine
Acetylcholine is a neurotransmitter, a chemical messenger that transmits signals between nerve cells. In the brain, acetylcholine is linked to functions like memory, learning, and attention. Throughout the rest of the body, it helps regulate involuntary actions such as digestion, salivation, and the contraction of certain muscles.
Medications with anticholinergic properties work by blocking acetylcholine from binding to its receptors on nerve cells, similar to a key being blocked from entering a lock. When the neurotransmitter cannot access the receptor, it cannot deliver its message. This interruption disrupts the normal signaling process, leading to the various symptoms associated with these effects.
The body has two main types of acetylcholine receptors: muscarinic and nicotinic. Anticholinergic drugs primarily block muscarinic receptors, which are found in the central and peripheral nervous systems. This widespread presence explains why the side effects can appear in many different parts of the body.
Common Anticholinergic Symptoms
The symptoms of anticholinergic effects can be divided into two main categories: those that affect the body (peripheral) and those that affect the brain (central). The severity of these symptoms often depends on the dose of the medication.
Peripheral Effects
Peripheral symptoms arise from the disruption of acetylcholine’s function in the body’s automatic processes. Common examples include:
- A dry mouth and dry eyes, due to reduced saliva and tear production
- Blurred vision because the muscles that focus the eyes are affected
- Constipation, as the drug slows down the movement of the gastrointestinal tract
- Difficulty urinating (urinary retention)
- An increased heart rate
- Flushing of the skin
- A decreased ability to sweat, which can lead to overheating
Central Effects
Central effects occur when the medication crosses the blood-brain barrier and interferes with acetylcholine’s role in the brain. These symptoms can include drowsiness, dizziness, and confusion. In some cases, individuals may experience restlessness or agitation.
These central nervous system effects are a concern for older adults. With age, the body naturally produces less acetylcholine, so blocking its effects can have a more pronounced impact. This increases the risk of confusion, memory impairment, delirium, and falls in this population.
Medications with Anticholinergic Properties
A wide variety of both prescription and over-the-counter (OTC) medications possess anticholinergic properties. Often, these effects are unintended side effects of a drug designed for another purpose.
One of the most well-known categories is first-generation antihistamines, such as diphenhydramine, which is found in many allergy and cold remedies. Tricyclic antidepressants, like amitriptyline, are another major class of drugs with strong anticholinergic activity. Medications used to treat an overactive bladder, such as oxybutynin, are specifically designed to block acetylcholine receptors to reduce bladder muscle spasms.
Other examples include some muscle relaxants, medications for Parkinson’s disease, and certain antipsychotics. The issue becomes more complex when a person takes multiple medications with these effects simultaneously.
This leads to the concept of “anticholinergic burden,” which is the cumulative effect of all anticholinergic drugs a person is taking. A higher burden, even from several drugs with mild effects, increases the risk of experiencing more severe side effects.
Managing Anticholinergic Side Effects
The primary step in managing anticholinergic side effects is to speak with a healthcare provider. It is not advisable to stop taking a prescribed medication without medical guidance, as this can have other health consequences. A doctor can review all current medications, assess the anticholinergic burden, and determine if an alternative treatment with fewer of these effects is appropriate.
For mild symptoms, several non-pharmacological strategies can provide relief. Sipping water frequently or chewing sugar-free gum can help alleviate dry mouth. For dry eyes, over-the-counter artificial tears can offer comfort. To address constipation, increasing the intake of dietary fiber and drinking plenty of water is often effective.
In some situations, a doctor might recommend adjusting the dosage of a medication. The goal is to find a balance where the therapeutic benefits of the drug are maintained while minimizing the discomfort of its side effects. Regular medication reviews are important for older adults to prevent the accumulation of anticholinergic burden and its associated risks.