Mental health: Side effects of medicines

Last updated: Friday, May 03, 2019

You may be asked for advice on how to manage side effects in patients taking psychiatric medicines. Compared to other therapeutic areas, the medicines used in mental health are particularly likely to be linked to groups of related adverse effects or syndromes, rather than individual complaints.

For example, certain antipsychotics can cause well-established patterns of extrapyramidal side effects. These are characterised by movement disorders such as:

  • Acute dystonia (involuntary muscle contraction). 
  • Akathisia (increased restlessness often in lower limbs, feeling of ‘unease’ and irritability).
  • Parkinsonism (bradykinesia, tremor, rigidity). 
  • Tardive dyskinesia (involuntary movement including myoclonic jerks, tics, chorea and dystonia).


Another example is the Syndrome of Inappropriate AntiDiuretic Hormone secretion (SIADH). Antidepressants, antipsychotics and carbamazepine are amongst the many medicines that can stimulate the over-secretion of antidiuretic hormone which causes significant fluid retention, resulting in hyponatraemia. This triggers symptoms such as weakness, weight gain, cramps, vomiting and anorexia. It can lead to confusions, coma and death so it's important to pick this problem up early.

Anticholinergic burden


Many medicines have anticholinergic side effects, and these are additive when more than one of these types of medicine is taken together. Mental health medicines such as tricyclic antidepressants, many antipsychotics, and procyclidine can all cause these symptoms, as well as medicines used for non-mental health reasons such as hyoscine and older antihistamines like chlorphenamine.

Acetylcholine is a neurotransmitter that mediates activities such as peristalsis, bladder emptying, slowing of the heart, saliva production, control of body temperature, and focusing of the eye. Acetylcholine is also found in the brain where, amongst other actions, it helps alertness, concentration, and learning. Given the widespread role of acetylcholine in controlling basic body functions, medicines with anticholinergic properties can cause a broad range of side effects. Many of  these anticholinergic side effects are summarised in the infographic below: