Cannabis will be used to treat symptoms of dementia in the first major UK trial to test its use, scientists have announced.

Pensioners with symptoms of Alzheimer’s disease will be recruited to see how cannabis-based treatment compares with a dummy drug.

Scientists are testing whether Sativex - a Peppermint-flavoured mouth spray containing cannabinoids - could be used to reduce symptoms of agitation or aggression.

Around half of the 850,000 dementia sufferers in the UK experience such symptoms, as well as memory problems and confusion.

The drug is already prescribed to some patients with multiple sclerosis to relieve muscle stiffness and spasms.

Alzheimer’s Research UK is committing £300,000 funding to the Kings College London trial, involving elderly patients living in care homes.

The study team will recruit 60 volunteers with Alzheimer’s disease between 55 and 90 years old who are living in care homes and have symptoms of agitation or aggression.

Volunteers will take the medication for four weeks, with results compared with those given a placebo drug.

Lead researcher Prof Dag Aarsland said: “While people most often associate Alzheimer’s disease with memory problems, this is just one aspect of a complex condition that can affect people in different ways.