Benzodiazepines.
The single most important fact about benzodiazepines is what they cannot do. They cannot open the chloride channel without GABA present, and that ceiling is the reason they displaced barbiturates and the reason overdose on a benzodiazepine alone is usually survivable.
The mechanism in one sentence
Benzodiazepines increase the frequency of chloride channel opening at the GABA-A receptor, amplifying inhibition that GABA itself must initiate.
GABA-A is a ligand-gated chloride channel and the main inhibitory receptor in the brain. When GABA binds, the channel opens, chloride enters and the neuron becomes harder to fire. Benzodiazepines bind a separate allosteric site and increase how often the channel opens in response to GABA, without opening it themselves. Barbiturates bind elsewhere again and increase how long the channel stays open, and at high concentrations can open it without GABA at all. That difference, frequency versus duration and the presence or absence of a ceiling, is the whole safety story of the two classes.
Members of the class
| Drug | What sets it apart |
|---|---|
| Diazepam | Long-acting with active metabolites; used in withdrawal and status epilepticus. |
| Lorazepam | Intermediate-acting, no significant active metabolites, preferred in liver impairment. |
| Midazolam | Short-acting, used for procedural sedation. |
| Temazepam | Short to intermediate, used for insomnia. |
| Chlordiazepoxide | Long-acting, standard in alcohol withdrawal regimens. |
What the class is used for
- Short-term severe anxiety and insomnia
- Status epilepticus and acute seizure termination
- Alcohol withdrawal, exploiting cross-tolerance at the same receptor
- Procedural sedation and muscle spasm
Side effects, derived from the mechanism
Each entry below follows from the mechanism above rather than being a separate fact. Read the middle column as the answer to the question, why would that happen.
| Effect | Why it follows |
|---|---|
| Sedation and impaired coordination | Generalised central inhibition; the therapeutic effect appearing in motor and cognitive systems too. |
| Anterograde amnesia | Inhibition of hippocampal encoding, which is useful for procedures and unwanted otherwise. |
| Falls in older adults | Sedation plus impaired postural control, on a background of slower clearance and higher sensitivity. |
| Tolerance and dependence | Receptor adaptation to sustained potentiation, which is why courses are kept short. |
| Respiratory depression in combination | Benzodiazepines alone have a ceiling, but combined with opioids or alcohol the inhibition compounds and the ceiling no longer protects. |
Contraindications and cautions
- Severe respiratory insufficiency and sleep apnoea
- Caution in older adults, in liver impairment and alongside opioids
- Avoid abrupt cessation after prolonged use
The part you cannot derive
Withdrawal after prolonged use can include seizures and is potentially life-threatening, which is unusual among drugs of dependence. Long-acting agents are used to taper precisely because their slow offset smooths the decline.
Exam traps
Frequency versus duration
Benzodiazepines increase frequency of channel opening; barbiturates increase duration. This single distinction explains the difference in overdose lethality.
Flumazenil is not routine
Reversing benzodiazepine activity abruptly can precipitate seizures in a dependent patient or in mixed overdose, so it is used selectively.
Lorazepam in liver disease
Agents without active metabolites and with simpler conjugation are preferred when hepatic function is impaired.
Members of this class that get confused
Within a class, the members differ on one property at a time, and that property is what exam questions are usually built on. These pairs split cleanly.
- Diazepam vs Lorazepam — Diazepam is metabolised by the liver into long-lasting active metabolites, so its effect accumulates and persists.
Test yourself on this
Reading a mechanism and being able to retrieve it under time are different skills, and only the second one is examined. These are free and need no account.
- CNS pharmacology practice questions — 10 questions with explanations
- Anticholinergic burden in older adults
- False positives on urine drug screens
- Half-life and steady state calculator — free calculator with a worked example
Common questions
How do benzodiazepines differ from barbiturates?
Benzodiazepines increase how often the GABA-A chloride channel opens and still require GABA to be present, which puts a ceiling on their effect. Barbiturates increase how long the channel stays open and at high doses can open it without GABA, which removes that ceiling and makes overdose far more dangerous.
Why is benzodiazepine overdose usually survivable?
Because the drug only amplifies a signal GABA has already started. Once every available receptor is potentiated, more drug adds little. That protection disappears when opioids or alcohol are taken alongside.
Is benzodiazepine withdrawal dangerous?
It can be. Unlike most drugs of dependence, abrupt withdrawal after prolonged use can cause seizures, which is why treatment is tapered and often switched to a longer-acting agent first.
Other drug classes
Beta blockers · ACE inhibitors · Statins · Anticoagulants · Diuretics · Opioids · All drug classes
Study aid only. This page is written for learning and examination practice. It is not medical advice, not clinical decision support, and must never be used to make a decision about a real patient. Always verify against your local formulary, the product literature and a qualified pharmacist. See our medical disclaimer.
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