What Are Anticholinergics?

Anticholinergics are drugs used to treat involuntary muscle movements. In some cases, these involuntary movements are a result of a physical health condition such as Parkinson's disease or asthma. Other times, they are a side effect of psychiatric medications.

If you have been prescribed an anticholinergic, it's helpful to understand how these medications work and what type of conditions they can help manage or treat. It's also important to know the potential side effects of anticholinergics and precautions associated with this category of drugs.

History of Anticholinergics

Anticholinergics were originally derived from atropine-containing plants like deadly nightshade and thorn apple. As far back as the 17th century, these plants were burned and the smoke was inhaled as a treatment for diseases obstructing the airways.

Over the next several centuries, patients with asthma started using cigarettes and tobacco pipes to inhale the smoke from the burned plants. While this was a popular over-the-counter option, the dosage of atropine the patient received varied depending on how deeply they inhaled and whether they absorbed any of the atropine in their mouths or gastrointestinal tracts.

In the 19th century, anticholinergic agents were introduced into medications for Parkinson’s disease. As other more effective drugs have been developed, the use of anticholinergics to treat Parkinson’s has declined. This is largely due to the more severe side effects that these medications can have on older people. 

How Anticholinergics Work

Anticholinergics work by blocking the action of a chemical messenger called acetylcholine. Acetylcholine is responsible for transferring signals that affect communication between nerves and certain types of muscles and organs in several parts of the body.

One of the most common uses of anticholinergics is as a treatment for asthma. These medications help ease asthma symptoms by relaxing and enlarging the airway, which makes breathing easier. 

Types of Anticholinergics 

Anticholinergics can be split into two broad categories: drugs that are primarily anticholinergic and drugs that are designed for other purposes but produce anticholinergic effects. 

Primary Anticholinergics

There are several pure anticholinergic medications and they all work in the same way—by blocking the actions of acetylcholine. These anticholinergics generally cannot be bought over the counter; they can only be prescribed by a physician.

The anticholinergic a healthcare provider might prescribe depends on the condition that is being treated. While there are many that exist, some options include:

• Atropine: Used to treat eye conditions such as uveitis, and to reduce the secretion of saliva and mucus in the airways during surgery.
• Bentyl (dicyclomine): Used to treat irritable bowel syndrome (IBS) symptoms.
• Cogentin (benztropine mesylate) and Trihexyphenidyl HCL: Used to treat symptoms of Parkinson's disease, and to help manage the side effects of certain psychiatric medications.
  

• Ditropan (oxybutynin): Used to treat overactive bladder.
• Enablex (darifenacin): Used to treat urinary incontinence. 
• Tudorza Pressair (aclidinium): Used to treat respiratory conditions, like asthma.

Drugs With Anticholinergic Effects

Some prescription and over-the-counter medications also have anticholinergic properties. This means that they can block the actions of acetylcholine, even though they are not formulated for that purpose.

Medications that fall into this category include: 

• Antipsychotic medications: Thorazine (chlorpromazine), Clozaril (clozapine), Zyprexa (olanzapine)
• First-generation antihistamines: Benadryl (diphenhydramine), Vistaril (hydroxyzine), and Tavist (clemastine)
• Tricyclic antidepressants: Elavil (amitriptyline), Anafranil (clomipramine), and Tofranil (imipramine)

Uses for Anticholinergics

Anticholinergics may be used to help treat several health conditions, including: 

• Allergies
• Asthma 
• Chronic obstructive pulmonary disease (COPD)
• Diarrhea 
• Gastrointestinal disorders 
• Hyperhidrosis (excessive sweating)
• Motion sickness 
• Muscle spasms 
• Overactive bladder 
• Parkinson's disease
• Poisoning
• Urinary incontinence 

Anticholinergics can also be used during surgery to reduce bronchial secretions and dilate the airways, decreasing airway resistance during the procedure. 

Side Effects of Anticholinergics

People taking anticholinergics can experience side effects. Some of these effects are more common than others, some are severe, and some effects can be long-term.

Common Side Effects

The side effects experienced most often with anticholinergic medications include:

• Cognitive impairment
• Constipation
• Dry mouth
• Functional difficulties, or trouble performing everyday activities
• Urinary retention (when the bladder does not fully empty during urination)

Severe Side Effects

When anticholinergics are used at high doses, one may experience severe side effects. Severe side effects are also more common in older people, which is why anticholinergics are used with caution, if at all, in the elderly.

Some of the serious side effects that can occur with anticholinergics include: 

• Blood pressure changes (either low or high)
• Delirium
• Dilated pupils
• Fever
• Hallucinations
• Increased heartbeat
• Trouble regulating body temperature, due to increased heat production and inability to sweat

Long-Term Side Effects

Some research suggests that long-term use of anticholinergics may contribute to cognitive decline. A 2018 study evaluated the risk of older people who used anticholinergics long-term and found an association between long-term use and an increased risk of developing dementia.

Long-term use of anticholinergics is also not recommended for people with schizophrenia. The reason for this is that, over time, the use of anticholinergics can make these individuals' cognitive impairment worse, impacting their quality of life.

Precautions for Anticholinergics

Certain precautions need to be taken when using anticholinergics. They include:

• Overheating: It’s important to prevent your body from overheating by staying hydrated when on anticholinergics, especially if one of the side effects you experience is decreased sweating. When there’s a decrease in how much you sweat, your body temperature rises and you are more likely to experience heat strokes. 
• Overdose: Taking several anticholinergic drugs at once—such as by taking numerous over-the-counter cold medicines—can result in an overdose. Signs of overdose include confusion, hallucinations, rapid heartbeat, fever, and dizziness. 
• Use with alcohol: Like with almost all medications, the use of anticholinergics with alcohol is strongly discouraged.
• Other medical conditions: People with certain medical conditions may be discouraged from using anticholinergics. Talk with your physician if you have any medical conditions before taking anticholinergic drugs.
• Use with other drugs: People who are already taking certain other drugs shouldn’t take anticholinergics. Let your healthcare provider or pharmacist know if you are taking other medications and have been prescribed an anticholinergic agent.