Published: 7 March 2024


Unexplained mood and behavioural changes – could it be a side effect?

Published 7 March 2024
Prescriber Update 45(1): 5–8
March 2024

Key messages

  • Some non-psychotropic medicines can cause psychiatric side effects such as changes in mood and behaviour.
  • Very old and very young patients and those with past or present psychiatric disorders may be more susceptible to psychiatric side effects.
  • Advise patients and their whānau or caregivers to seek medical advice if they notice any changes in mood or behaviour when starting medicines with psychiatric effects.
  • Consider medicine side effects as part of the differential diagnosis in people presenting with new or worsening psychiatric symptoms.

Medicines can cause psychiatric side effects, including mood and behavioural changes.1

This article highlights the psychiatric side effects of non-psychotropic medicines frequently prescribed in primary care settings.

Medicines with psychiatric side effects

Psychiatric side effects of medicines are defined as new psychiatric symptoms that develop during treatment or worsening of pre-existing psychiatric disorders.1 In some cases, symptoms may also occur on withdrawal of a medicine.2

Side effects may resemble symptoms associated with psychiatric disorders, such as agitation, euphoria, confusion, delusional thoughts, hallucinations, low mood and depression.2

Risk factors that may predispose patients to develop psychiatric side effects with medicines include present or past history of psychiatric disorders, extremities of age (very young or very old) and higher doses.2

Table 1 provides examples of medicines (excluding psychotropics) where the data sheets list psychiatric side effects as known adverse reactions. Note: Table 1 is not a complete list of all medicines and adverse reactions.

Table 1: Examples of medicines (excluding psychotropic medicines) that can cause psychiatric side effects

Medicine class Examples of medicine(s) Examples of psychiatric side effects listed in data sheet
ACE inhibitors Enalapril, quinapril Depression, confusion, insomnia
Antivirals Aciclovir, valaciclovir Confusion, hallucinations, agitation, psychotic disorder
Antibiotics Sulfamethoxazole + trimethoprim Depression, hallucination, psychotic disorder, insomnia, apathy, mental depression, hallucinations
Metronidazole Psychotic disorder, confusion, hallucinations, depression, insomnia, irritability
Rifampicin, isoniazid Psychotic disorder
Anticholinergic Oxybutynin Agitation, anxiety, hallucinations, nightmares, paranoia, depression, confusion, behavioural disorders
Hyoscine hydrobromide Confusion, hallucinations
Antihistamines Cetirizine Agitation, aggression, confusion, depression, hallucination, insomnia, tic, suicidal ideation, nightmare
Promethazine Euphoria, excitation, catatonic-like states, hysteria, agitation, confusional states
Beta-blockers Metoprolol, bisoprolol Depression, hallucinations, insomnia, nightmares
Calcium channel blockers Amlodipine, diltiazem Mood changes
Cardiac glucosides Digoxin Depression, psychotic disorder, apathy, confusion
Combined oral contraceptives Levonorgestrel + ethinylestradiol Norethisterone + ethinylestradiol Depressed mood, altered mood
Corticosteroids Prednisone, dexamethasone Euphoria, depression, mania, delusions, hallucinations, insomnia, suicidal ideation
Leukotriene receptor antagonists Montelukast Nightmares, agitation, depression, psychomotor hyperactivity, hallucinations, obsessive-compulsive symptoms, suicidal behaviour
Proton pump inhibitors Omeprazole, pantoprazole Agitation, confusion, depression, hallucinations
Other Isotretinoin Depression, behavioural disorders, suicidality
Tacrolimus Insomnia, confusion, depression, mood disorders, mood disturbances, nightmare, hallucination, psychiatric disorder

Note: This table is not a complete list of all medicines and adverse reactions.

Source: Medsafe data sheets and consumer medicine information search. URL: (accessed 11 January 2024).

Advise patients, whānau and caregivers about psychiatric side effects

When starting medicines with known psychiatric side effects, advise patients and their whānau and/or caregivers about possible signs and symptoms and what to do if these occur.

Whānau, friends and caregivers can play an important role in alerting patients to possible changes in their mood and/or behaviour.

Advise parents and/or caregivers to closely monitor young children, including asking the child about possible side effects.

Psychiatric side effects may be difficult to identify

Consider medicine side effects as part of the differential diagnosis in patients presenting with new or worsening psychiatric symptoms.3

It may be challenging to establish if the symptoms are medicine-related.3 Consult the medicine data sheet to check if psychiatric effects are known to be associated with the suspected medicine.

One or more of the following features may suggest a medicine-related effect:3

  • a temporal relationship between medicine exposure and side effect
  • positive de-challenge (symptoms improve after stopping the medicine)
  • positive re-challenge (symptoms recur after restarting the medicine).

Psychiatric side effects are generally reversible after discontinuation of the suspected medicine.3

Further information

Healthify: Medicines that affect mood

Previous Prescriber Update articles:


  1. Zareifopoulos N, Lagadinou M, Karela A, et al. 2020. Neuropsychiatric effects of antiviral drugs. Cureus 12(8): e9536. DOI: 10.7759/cureus.9536 (accessed 11 January 2024).
  2. Casagrande Tango R. 2003. Psychiatric side effects of medications prescribed in internal medicine. Dialogues in Clinical Neuroscience 5(2): 155-65. DOI: 10.31887/DCNS.2003.5.2/rcasagrandetango (accessed 11 January 2024).
  3. Gupta A, Chadda RK. 2016. Adverse psychiatric effects of non-psychotropic medications. BJPsych Advances 22(5): 325-34. DOI: 10.1192/apt.bp.115.015735 (accessed 11 January 2024).
Hide menus
Show menus
0 1 2 4 5 6 7 9 [ /