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Anticholinergic (muscarinic antagonist)

Scopolamine

Scopolamine (hyoscine) is a tertiary amine antimuscarinic agent derived from plants of the Solanaceae family. It is primarily used for prevention of motion sickness and postoperative nausea and vomiting. Its high CNS penetration distinguishes it from other antimuscarinics and accounts for both its efficacy and its central adverse effects.

Practice questionsHigh-yield facts
Drug classAnticholinergic (nonselective muscarinic antagonist)
MechanismBlocks M1-M5 muscarinic receptors centrally and peripherally
Main usesMotion sickness, PONV, cycloplegia, antisialagogue
Key adverse effectCentral anticholinergic syndrome (confusion, hallucinations, sedation)
6 min readFor medical studentsUpdated 2026-10-14

Mechanism of action

Scopolamine is a competitive antagonist at all five muscarinic acetylcholine receptor subtypes (M1–M5). Unlike quaternary ammonium antimuscarinics such as glycopyrrolate, scopolamine is a tertiary amine that readily crosses the blood-brain barrier, producing significant central nervous system effects.

Key receptor actions:

  • M1 receptors (CNS, gastric parietal cells): blockade reduces gastric acid secretion and contributes to cognitive effects
  • M2 receptors (heart): blockade can cause tachycardia, though bradycardia may occur at low doses via central mechanisms
  • M3 receptors (smooth muscle, glands): blockade reduces GI motility, salivary and bronchial secretions, causes mydriasis and cycloplegia
  • M4 and M5 (CNS): contribute to central sedative and amnestic effects

In the vestibular system, scopolamine blocks muscarinic transmission in the vestibular nuclei and in pathways to the vomiting center, interrupting the neural signals that trigger motion sickness. Its antisialagogue effect makes it useful in preoperative settings to reduce oral and respiratory secretions.

High-yield for exams
  • Scopolamine is a tertiary amine antimuscarinic that crosses the blood-brain barrier, causing central sedation and amnesia.
  • The transdermal patch must be applied 4+ hours before anticipated need for motion sickness; it is prophylactic, not acute treatment.
  • Classic presentation: unilateral mydriasis after touching patch then rubbing one eye; anisocoria resolves spontaneously.
  • Central anticholinergic syndrome: confusion, hallucinations, hyperthermia, dry skin, mydriasis; treat with physostigmine.
  • Scopolamine causes bradycardia at low doses (central effect) but tachycardia at higher doses (peripheral M2 blockade).
  • Avoid in elderly due to high risk of delirium and cognitive impairment (Beers Criteria); contraindicated in angle-closure glaucoma.
  • Glycopyrrolate does not cross the BBB and is ineffective for motion sickness, unlike scopolamine.
  • Scopolamine has antisialagogue effects (reduces secretions), making it useful preoperatively and in hypersalivation.

Indications

Approved uses:

  • Motion sickness prophylaxis: transdermal patch is the most common formulation for this indication
  • Postoperative nausea and vomiting (PONV): used as part of multimodal antiemetic prophylaxis
  • Preoperative antisialagogue: reduces secretions before anesthesia
  • Ophthalmic applications: produces mydriasis and cycloplegia for refraction and examination (ophthalmic solution)
  • Antispasmodic: occasionally used for gastrointestinal or genitourinary smooth muscle spasm

Off-label uses:

  • Hypersalivation in Parkinson disease or other neurologic conditions
  • Nausea in palliative care

Scopolamine is generally more effective when used prophylactically rather than for treatment of established nausea or motion sickness.

Pharmacokinetics

Absorption and distribution:

  • Transdermal patch delivers approximately 1 mg over 72 hours after an initial loading phase
  • Oral and parenteral (IV, IM, subcutaneous) routes are also used
  • Tertiary amine structure allows excellent CNS penetration
  • Volume of distribution suggests wide tissue distribution

Metabolism and excretion:

  • Hepatic metabolism, primarily via hydrolysis and conjugation
  • Renal excretion of metabolites and small amounts of unchanged drug
  • Elimination half-life approximately 4.5–9.5 hours depending on route and formulation

Clinical considerations:

  • Transdermal patch should be applied at least 4 hours before anticipated need, ideally the evening before travel
  • Hands must be washed after handling patches to avoid accidental ocular contamination and unilateral mydriasis
  • Effects may persist for 24 hours or more after patch removal due to depot effect in skin

Adverse effects

Adverse effects follow predictably from antimuscarinic blockade. Central effects are more prominent with scopolamine than with peripheral antimuscarinics.

Common (peripheral antimuscarinic):

  • Dry mouth (xerostomia), most frequent complaint
  • Blurred vision, mydriasis, cycloplegia
  • Urinary retention
  • Constipation
  • Tachycardia
  • Dry skin, decreased sweating (risk of hyperthermia in hot environments)

Central nervous system (more common with scopolamine than other antimuscarinics):

  • Sedation and drowsiness: dose-dependent
  • Confusion, disorientation, memory impairment: especially in elderly
  • Hallucinations, agitation, delirium: central anticholinergic syndrome
  • Dizziness

Serious:

  • Acute angle-closure glaucoma: precipitation in susceptible individuals
  • Central anticholinergic toxicity: confusion, hallucinations, hyperthermia, seizures (high doses)
  • Severe hyperthermia in hot environments due to impaired sweating

Ophthalmic formulations:

  • Local irritation, increased intraocular pressure, photophobia

Transdermal patch-specific:

  • Contact dermatitis at application site
  • Withdrawal symptoms if discontinued abruptly after prolonged use (dizziness, nausea, headache)

Elderly patients are at higher risk for central effects including confusion and falls.

Contraindications and warnings

Absolute contraindications:

  • Hypersensitivity to scopolamine or belladonna alkaloids
  • Angle-closure glaucoma or untreated narrow anterior chamber angle

Relative contraindications and warnings:

  • Elderly patients: increased sensitivity to central anticholinergic effects; use with caution and consider lower doses
  • Benign prostatic hyperplasia or bladder neck obstruction: risk of urinary retention
  • Gastrointestinal obstruction, paralytic ileus, severe ulcerative colitis, toxic megacolon: antimuscarinic effects may worsen obstruction
  • Myasthenia gravis: may worsen muscle weakness
  • Cognitive impairment or dementia: anticholinergics worsen cognition and should generally be avoided (Beers Criteria)
  • Tachyarrhythmias, coronary artery disease: tachycardia may exacerbate ischemia
  • Hyperthyroidism: increased sensitivity to tachycardia
  • Hepatic or renal impairment: reduced clearance may prolong effects

Pregnancy and lactation:

  • Pregnancy category C (US, historical): animal studies show risk; use only if benefit justifies potential fetal risk
  • Scopolamine crosses the placenta; may cause respiratory depression or neonatal hemorrhage if used near term
  • Excreted in breast milk in small amounts; may reduce milk production and cause infant sedation or other anticholinergic effects; use caution

Special populations:

  • Children may be more susceptible to CNS effects (paradoxical excitation or sedation)
  • Down syndrome patients have increased sensitivity to anticholinergics

Drug interactions

Scopolamine has primarily pharmacodynamic interactions due to its anticholinergic activity.

Additive anticholinergic effects (increased risk of toxicity):

  • Other antimuscarinics (atropine, glycopyrrolate, oxybutynin, tolterodine)
  • Tricyclic antidepressants (amitriptyline, nortriptyline)
  • First-generation antihistamines (diphenhydramine, hydroxyzine, promethazine)
  • Antipsychotics with anticholinergic properties (chlorpromazine, clozapine, olanzapine)
  • Antiparkinson drugs (benztropine, trihexyphenidyl)
  • Muscle relaxants (cyclobenzaprine, orphenadrine)

CNS depressants (additive sedation):

  • Benzodiazepines, barbiturates, opioids, alcohol
  • May impair mental alertness and motor coordination

Medications affected by altered GI motility:

  • Reduced GI motility may delay or reduce absorption of some oral drugs, or increase absorption of others via prolonged contact time
  • Sublingual nitroglycerin absorption may be reduced (dry mouth)

Cholinergic agonists:

  • Scopolamine antagonizes effects of bethanechol, neostigmine, and other cholinergic drugs

Digoxin:

  • Bradycardia from digoxin may be antagonized; monitor for reduced effect

CYP enzyme interactions:

  • Minimal clinically significant cytochrome P450 interactions; scopolamine is not a major substrate, inhibitor, or inducer

Clinical pearls

Exam and clinical high-yield points:

  • Scopolamine is the anticholinergic of choice for motion sickness because of its CNS penetration and vestibular effects; glycopyrrolate does not cross the blood-brain barrier and is ineffective for motion sickness
  • The transdermal patch is convenient but must be applied hours before exposure (not for acute treatment)
  • Classic exam scenario: patient with unilateral dilated pupil after touching a scopolamine patch and then rubbing one eye
  • Central anticholinergic syndrome presents with the mnemonic "hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter"; treat with physostigmine (acetylcholinesterase inhibitor)
  • Scopolamine produces amnesia as well as sedation, making it useful (and sometimes problematic) in the perioperative setting
  • Elderly patients are especially vulnerable to delirium and falls; scopolamine should generally be avoided in this population (Beers Criteria)
  • Abrupt discontinuation of the transdermal patch after prolonged use (>3 days) may cause withdrawal symptoms (rebound nausea, headache, dizziness)
  • Scopolamine has been historically used as a "truth serum" and in obstetrics for "twilight sleep" (amnesia during labor), though these uses are now obsolete
  • In contrast to atropine, scopolamine causes bradycardia at low doses due to central vagal stimulation before peripheral blockade predominates
  • The tertiary amine structure of scopolamine (vs. quaternary ammonium structure of glycopyrrolate) explains its CNS activity

Practical considerations:

  • Warn patients about drowsiness and advise against driving or operating machinery
  • Instruct patients applying transdermal patches to wash hands thoroughly after application to prevent accidental eye contamination
  • Use is generally limited to 72 hours for transdermal patches; prolonged use increases risk of tolerance and withdrawal
  • In surgical settings, scopolamine may be combined with other antiemetics (5-HT3 antagonists, dexamethasone) for multimodal PONV prophylaxis
Mnemonic

Anticholinergic toxicity: "Hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter."

Practice questions

1. A 68-year-old woman with a history of Parkinson disease is prescribed a scopolamine patch for an upcoming cruise. Three days after applying the patch, she presents to the emergency department with confusion, visual hallucinations, and agitation. Her temperature is 38.2°C (100.8°F), heart rate 110/min, and blood pressure 145/88 mmHg. Physical exam reveals dilated pupils, dry mucous membranes, and flushed skin. Which of the following is the most appropriate initial treatment?

Answer: C. This patient has central anticholinergic syndrome from scopolamine toxicity, characterized by confusion, hallucinations, hyperthermia, tachycardia, mydriasis, dry skin, and flushed appearance. Physostigmine, an acetylcholinesterase inhibitor that crosses the blood-brain barrier, is the antidote and reverses central anticholinergic toxicity. Haloperidol and diphenhydramine have anticholinergic properties and would worsen the syndrome. Lorazepam would sedate but not reverse the underlying cause.

2. A 45-year-old man applies a scopolamine transdermal patch behind his right ear in preparation for a fishing trip. The next morning, he notices that his right pupil is significantly larger than his left. He denies eye pain, vision changes, or headache. The rest of his neurologic exam is normal. Which of the following is the most likely explanation?

Answer: D. Unilateral mydriasis after applying a scopolamine patch is a classic presentation caused by touching the patch and then rubbing the ipsilateral eye, transferring drug to the conjunctiva. The affected pupil is dilated and poorly reactive but the patient is otherwise asymptomatic. This is a benign, self-limited phenomenon. Third nerve palsy would present with ptosis and ophthalmoplegia. Horner syndrome causes miosis, not mydriasis. Angle-closure glaucoma would cause pain and vision changes.

3. A 72-year-old woman with mild dementia undergoes elective cholecystectomy. Postoperatively, she receives a scopolamine patch for nausea prophylaxis. On postoperative day 1, nursing staff report that she is increasingly confused, cannot find her way to the bathroom, and does not recognize her family. Vital signs are within normal limits. Which of the following is the most appropriate next step in management?

Answer: C. This patient has postoperative delirium precipitated by scopolamine, an anticholinergic drug that should be avoided in elderly patients with dementia (Beers Criteria). The most appropriate step is to remove the patch and discontinue the offending agent; delirium often improves with supportive care once the drug is cleared. Haloperidol is anticholinergic and would worsen the problem. Head CT and antibiotics are not indicated in a hemodynamically stable patient with a clear medication-related cause.

Frequently asked questions

How does scopolamine work?

Scopolamine works by blocking muscarinic acetylcholine receptors (M1–M5) both centrally and peripherally. Its tertiary amine structure allows it to cross the blood-brain barrier, where it inhibits vestibular pathways and the vomiting center, preventing motion sickness and nausea. Peripheral blockade reduces secretions, causes mydriasis, and decreases gastrointestinal motility.

What are the side effects of scopolamine?

Common side effects include dry mouth, drowsiness, blurred vision, constipation, and urinary retention. Central nervous system effects are prominent and include sedation, confusion, memory impairment, and hallucinations, especially in the elderly. Serious risks include acute angle-closure glaucoma precipitation, central anticholinergic syndrome with high doses, and hyperthermia due to impaired sweating.

Is scopolamine a controlled substance?

No, scopolamine is not a controlled substance in the United States or most countries. It is available by prescription for medical uses such as motion sickness prevention and postoperative nausea. However, it has been misused illicitly in some regions for sedation and incapacitation, leading to regulatory concerns in certain jurisdictions.

Scopolamine vs atropine — what is the difference?

Both are nonselective muscarinic antagonists, but scopolamine has greater CNS penetration, causing more sedation, amnesia, and antiemetic effects, making it better for motion sickness. Atropine is preferred for bradycardia and anticholinesterase poisoning due to stronger cardiac effects and less sedation. At low doses, scopolamine may cause bradycardia (central effect) whereas atropine causes tachycardia.

How long does a scopolamine patch last?

A scopolamine transdermal patch is designed to deliver medication continuously for 72 hours (3 days). It should be applied at least 4 hours before travel or anticipated need. After removal, effects may persist for up to 24 hours due to a depot of drug remaining in the skin. Prolonged use beyond 72 hours is not recommended due to risk of tolerance and withdrawal.

Conditions it is used for

Motion sicknessPostoperative nausea and vomitingNauseaHypersalivationMydriasis (ophthalmic)Cycloplegia (ophthalmic)
AtropineGlycopyrrolateMeclizinePromethazineOndansetronDiphenhydramineBenztropineOxybutynin

Sources and further reading

DailyMed (FDA labels)StatPearls (NCBI Bookshelf)MedlinePlusWHO ATC/DDD index: A04AD01WHO ATC/DDD index: N05CM05

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.