Chemical cosh antipsychotic drugs given to dementia patients put them at a far higher risk of stroke than other people, according to research.
Up to 105,000 are inappropriately prescribed drugs used to treat agitation, anxiety, mania and aggression, according to the Alzheimer's Society.
It believes that thousands of elderly patients - often in care homes - are prescribed antipsychotic drugs to control them and keep them quiet.
A new study looking into the the various types of drugs available found that dementia patients were 3.5 times more likely to have a stroke while taking the drugs.
Published online in the British Medical Journal (BMJ), the study used GP records to work out the risk of stroke in patients on antipsychotics.
The risk of stroke associated with first generation (typical) antipsychotics, and whether the risk differs in people with and without dementia, has not been studied before.
The UK's Committee on Safety of Medicines had previously recommended that the atypical drugs risperidone or olanzapine should not be used in people with dementia.
It had also advised that a risk of stroke for other antipsychotics could not be excluded. Prescribers were advised to review the treatment of all patients with dementia receiving atypical antipsychotics.