Core69: Drug-induced adverse reaction: sedation

😴 High-yield / 要点：Sedation is a CNS-depressant adverse effect that commonly occurs with drugs used in psychiatry and neurology, but any CNS-penetrating drug can cause it.

Definition / 定義

• Sedation = reduced CNS activity with calming and sometimes hypnotic effect.
• Common symptoms:
  • Drowsiness.
  • Dizziness.
  • Reduced alertness.
• Important clinical issue:
  • Higher fall/injury risk, especially in older adults.

Key principles / 重要ポイント

• Sedative drugs can enhance each other’s effects.
• Alcohol also enhances sedation.
• This matters when dosing or combining drugs.

Main mechanisms / 主な機序

• Enhancement of GABA effect
• Reduction of glutamate release
• H1 receptor blockade
• μ-opioid receptor stimulation
• Central α2 receptor stimulation

Main sedating drug groups / 主な鎮静性薬

Group	Mechanism	Examples
Sedatives / hypnotics	Enhance GABA effect	Diazepam, alprazolam, midazolam, clonazepam, zolpidem
Antiepileptics	Enhance GABA or reduce glutamate release	Diazepam, clonazepam, phenobarbital, vigabatrin, gabapentin, pregabalin, carbamazepine, lamotrigine
Antipsychotics	H1 receptor blockade	Olanzapine, quetiapine, risperidone, chlorpromazine
Opioid analgesics	μ-opioid receptor stimulation	Morphine, fentanyl, codeine, tramadol
Centrally acting skeletal muscle relaxants	Central α2 stimulation	Tizanidine
Centrally acting antihypertensives	Central α2 and/or I1 receptor stimulation	Rilmenidine
Some antidepressants	H1 receptor blockade	Amitriptyline, mirtazapine, trazodone
1st-generation antihistamines	H1 receptor blockade	Diphenhydramine, promethazine

Remember / 覚え方

• Benzodiazepines, Z-drugs, opioids, sedating antipsychotics, 1st-gen antihistamines = classic causes
• Alcohol potentiates sedation
• Falls in the elderly are a major exam and clinical clue