Benzodiazepines learning module

3.8 Important drug interactions

Concomitant administration of a benzodiazepine with a drug which is sedative (eg alcohol) or which reduces blood pressure (eg ACE inhibitor) can increase the potential for these effects.

Consult summaries of product characteristics and other sources of information on the interactions of individual benzodiazepines.

Interacting drug or drug class

Effect of interaction

Risk-reduction measures

Drugs that reduce blood pressure:

  • ACE inhibitors and angiotensin-II receptor antagonists
  • Alpha1 adrenoceptor antagonists (eg alfuzosin, doxazosin, indoramin, prazosin, tamsulosin, terazosin)
  • Beta-blockers
  • Calcium-channel blockers
  • Clonidine
  • Diazoxide
  • Diuretics (thiazide eg bendroflumethiazide and loop eg furosemide)
  • Methyldopa
  • Moxonidine
    Nitrates (glyceryl trinitrate, isosorbide dinitrate, isosorbide mononitrate)

Increased hypotensive effect

Monitor blood pressure

Drugs that cause sedation (either as their primary effect or as an unwanted effect):

  • Alcohol
  • Anaesthetics, general
  • Antidepressants (including tricyclic antidepressants and mirtazapine)
  • Antihistamines, sedative
  • Antipsychotics
  • Lofexidine
  • Moxonidine
  • Opioid analgesics
  • Tizanidine

Increased sedation and increased risk of respiratory depression and hypotension. 

Combined disinhibitory effects of alcohol and a benzodiazepine may increase the possibility of aggressive behaviour.

Warn individual of excessive sedation and psychomotor impairment.

Effects on respiration and blood pressure may need to be monitored when initiating treatment or increasing the dose.


Increased sedation

Warn individual of excessive sedation and psychomotor impairment


Benzodiazepine effect increased



Benzodiazepine effect increased


Enzyme-inducing drugs such as:

  • Carbamazepine
  • Phenobarbital
  • Rifampicin

Enzyme induction may reduce benzodiazepine effect



Antiparkinsonian effect of levodopa may be reduced rarely



Benzodiazepines may raise or lower the concentration of phenytoin in blood



Effect of benzodiazepine increased—risk of excessive CNS depression

Avoid concomitant use, especially of alprazolam, diazepam and flurazepam

Sodium oxybate

Effect of sodium oxybate increased

Avoid concomitant use of a benzodiazepine and sodium oxybate

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Page last modified: 17 February 2015