Dicyclomine Side Effects

Overview

Dicyclomine causes side effects primarily due to its anticholinergic (antimuscarinic) properties. These effects result from blocking acetylcholine receptors throughout the body, not just in the gastrointestinal tract. Most side effects are dose-related and may improve with continued use or dose reduction.

Understanding potential side effects helps patients recognize what to expect and when to seek medical attention.

Common Side Effects

The most frequently reported side effects of dicyclomine include:

Dry mouth (xerostomia):

One of the most common anticholinergic effects
May be mild to moderate
Can be managed with frequent sips of water or sugar-free candy

Dizziness:

May occur especially when standing quickly
Usually mild and temporary

Blurred vision:

Due to effects on the muscles controlling the eye lens
Usually temporary
May affect ability to read or drive

Nausea:

May occur, especially when starting treatment
Taking with food may help

Drowsiness or sedation:

Can affect alertness
Use caution when driving or operating machinery

Nervousness:

Some patients experience restlessness or anxiety

Weakness:

General fatigue or lack of energy

Gastrointestinal Side Effects

Despite being used for GI symptoms, dicyclomine can cause:

Constipation:

Anticholinergic effect that slows intestinal movement
May be problematic for some IBS patients

Bloating:

Reduced GI motility can lead to trapped gas

Nausea:

Usually mild
May improve with continued use

Decreased appetite:

Some patients experience reduced hunger

Anticholinergic Effects

Dicyclomine produces classic anticholinergic side effects:

“Dry as a bone”:

Dry mouth
Dry eyes
Dry skin
Reduced sweating

“Blind as a bat”:

Blurred vision
Dilated pupils
Sensitivity to light

“Red as a beet”:

Flushed skin
Especially in hot environments

“Hot as a hare”:

Decreased sweating leading to heat intolerance
Increased body temperature in hot conditions

“Mad as a hatter”:

Confusion (especially in older adults)
Memory impairment
Delirium (at high doses or in susceptible individuals)

“Full as a flask”:

Urinary retention
Difficulty urinating

Cardiovascular Side Effects

Dicyclomine may affect the heart and blood vessels:

Tachycardia:

Rapid heartbeat
Palpitations

Other cardiovascular effects:

Changes in heart rhythm
Blood pressure fluctuations

Patients with pre-existing heart conditions should be monitored carefully.

Central Nervous System Effects

Beyond drowsiness and dizziness, dicyclomine can cause:

Confusion and memory problems:

More common in older adults
May affect cognitive function

Headache:

Occasionally reported

Insomnia:

Some patients have difficulty sleeping

Numbness or tingling:

Rarely reported

Speech disturbance:

Uncommon

Serious Side Effects

While rare, serious side effects can occur and require immediate medical attention:

Severe allergic reactions:

Rash, hives, or itching
Swelling of face, lips, tongue, or throat
Difficulty breathing
Anaphylaxis (rare)

Heat stroke:

Due to inability to sweat properly
Risk increases in hot environments or during exercise
Symptoms: high body temperature, confusion, rapid heartbeat, lack of sweating

Severe constipation or intestinal obstruction:

Significant abdominal pain
Inability to pass stool or gas
Abdominal distension

Urinary retention:

Inability to urinate
Painful bladder distension
More common in men with enlarged prostate

Psychiatric effects:

Psychosis (rare)
Severe confusion
Hallucinations

Eye problems:

Worsening of narrow-angle glaucoma
Increased eye pressure

Risk Factors for Side Effects

Certain factors increase the likelihood or severity of side effects:

Age

Older adults are significantly more susceptible to:

Cognitive effects (confusion, memory problems)
Falls due to dizziness
Urinary retention
Heat intolerance
Constipation

The American Geriatrics Society Beers Criteria recommends avoiding anticholinergics like dicyclomine in older adults when possible.

Pre-existing Conditions

Higher risk with:

Glaucoma (narrow-angle)
Enlarged prostate (benign prostatic hyperplasia)
Urinary obstruction
Cardiac arrhythmias
Gastrointestinal obstructive disorders
Autonomic neuropathy
Cognitive impairment or dementia

Concomitant Medications

Risk increases when combined with:

Other anticholinergic medications
Antihistamines
Tricyclic antidepressants
Antipsychotics
Muscle relaxants with anticholinergic properties

Environmental Factors

Hot weather increases heat stroke risk
Strenuous exercise when unable to sweat properly

Side Effects in Special Populations

Infants (Under 6 Months)

CONTRAINDICATED - Dicyclomine should never be used in infants under 6 months due to reports of:

Seizures
Syncope (fainting)
Respiratory symptoms
Muscular hypotonia (weak muscles)
Aspiration
Coma
Death

Children

Safety and efficacy not established in children. Use is not recommended.

Older Adults

Particular concerns include:

Increased sensitivity to anticholinergic effects
Higher risk of cognitive impairment
Falls due to dizziness
Urinary retention
Constipation
Heat stroke

Pregnant Women

Limited data on fetal effects. Use only if clearly needed.

Breastfeeding Women

Excreted in breast milk
May reduce milk production
Respiratory symptoms reported in nursing infants
Weigh benefits against risks

Drug Interactions That Increase Side Effects

Additive anticholinergic effects with:

Antihistamines (diphenhydramine, chlorpheniramine)
Tricyclic antidepressants (amitriptyline, nortriptyline)
Antipsychotics (chlorpromazine, olanzapine)
Antiparkinson drugs (benztropine, trihexyphenidyl)
Other antispasmodics
Muscle relaxants

Enhanced sedation with:

Alcohol
Opioids
Benzodiazepines
Sleep aids

Other interactions:

May increase digoxin levels (with slow-dissolving tablets)
May decrease absorption of medications requiring gastric acidity

Managing Side Effects

To reduce the likelihood and severity of side effects:

For dry mouth:

Sip water frequently
Use sugar-free candy or gum
Avoid caffeine and alcohol
Consider saliva substitutes

For constipation:

Increase fiber intake gradually
Stay well hydrated
Exercise regularly
Consider stool softeners if needed

For dizziness:

Rise slowly from sitting or lying positions
Avoid sudden movements
Hold onto stable objects when standing

For blurred vision:

Avoid driving until effects are known
Do not operate dangerous machinery
Effects usually diminish with continued use

For heat intolerance:

Avoid strenuous activity in hot weather
Stay in cool environments
Stay well hydrated
Watch for signs of heat stroke

When to Stop Taking Dicyclomine

Discontinue and contact your healthcare provider if:

Severe allergic reaction occurs
Signs of heat stroke develop
Unable to urinate or severe urinary difficulty
Severe constipation or intestinal obstruction symptoms
Significant confusion or memory problems
Rapid or irregular heartbeat
Severe eye pain or vision changes
Side effects are intolerable
Symptoms do not improve after adequate trial

Comparison with Other Medications

Compared to Loperamide:

Loperamide has fewer anticholinergic side effects
Dicyclomine more likely to cause dry mouth, blurred vision, urinary retention
Loperamide more likely to cause constipation related to slowed transit
Dicyclomine has more drug interactions

Compared to other antispasmodics:

Side effect profiles vary among antispasmodic medications
Peppermint oil (natural alternative) has different side effects
Hyoscyamine has similar anticholinergic effects

Sources

FDA-approved prescribing information for Bentyl (dicyclomine hydrochloride)
American Geriatrics Society Beers Criteria
Clinical pharmacology references
Drug safety databases