Medications with anticholinergic properties are associated with a range of adverse effects that tend to be worse in older people. To investigate medication regimens with high anticholinergic burden, prescribed for older adults under the care of mental health services. Clinical audit of prescribing practice, using a standardised data collection tool. Fifty-seven trusts/healthcare organisations submitted data on medicines prescribed for 7915 patients: two-thirds (66%) were prescribed medication with anticholinergic properties, while just under a quarter (23%) had a medication regimen with high anticholinergic burden (total score ≥3 on the anticholinergic effect on cognition (AEC) scale). Some 16% of patients with a diagnosis of dementia or mild cognitive impairment were prescribed medication regimens with a high anticholinergic burden, compared with 35% of those without such diagnoses. A high anticholinergic burden was mostly because of combinations of commonly prescribed psychotropic medications, principally antidepressant and antipsychotic medications with individual AEC scores of 1 or 2. Adults under the care of older people's mental health services are commonly prescribed multiple medications for psychiatric and physical disorders; these medication regimens can have a high anticholinergic burden, often an inadvertent consequence of the co-prescription of medications with modest anticholinergic activity. Prescribers for older adults should assess the anticholinergic burden of medication regimens, assiduously check for adverse anticholinergic effects and consider alternative medications with less anticholinergic effect where indicated. The use of a scale, such as the AEC, which identifies the level of central anticholinergic activity of relevant medications, can be a helpful clinical guide.