According to research, there is “Good evidence” that attention deficit hyperactivity disorder (ADHD) drugs could also be used to treat Alzheimer’s disease.

Pooled data analysis of the available research, published online in the Journal of Neurology Neurosurgery & Psychiatry says that there is “good evidence” that drugs used to treat ADHD could also successfully treat key aspects of Alzheimer’s disease.

The researchers say that clinical trials on noradrenergic drugs, which include medicines to treat ADHD and high blood pressure, as well as antidepressants, are now warranted.

Noradrenergic drugs work by targeting the neurotransmitter noradrenaline, which is released by a network of specialised noradrenergic neurons. The network is used in many cognitive processes including attention, learning, memory, readiness for action, and suppression of inappropriate behaviours.

Alzheimer's disease causes noradrenergic disruption, which leads to the cognitive and neuropsychiatric symptoms that are characteristic of the disease. This suggested to the researchers that the noradrenergic system would be a good target for drug treatment.

The researchers looked at clinical trials published between 1980 and 2021 where noradrenergic drugs, including atomoxetine, methylphenidate, and guanfacine, had been used to potentially improve cognitive and/or neuropsychiatric symptoms in people with neurodegenerative disease.

The clinical trials included a total of 19 randomised controlled trials focusing on Alzheimer’s disease and mild cognitive impairment, involving 1811 patients. Of the 19 trials, six were judged to be ’good’ quality, seven as ’fair’, and six as ’poor’.

The researcher pooled the results from 10 trials, involving 1300 people, for global cognition — orientation/attention, memory, verbal fluency, language and visuospatial ability.

The results showed a small, but significant, positive effect of noradrenergic drugs on overall cognition, as measured by the Mini-Mental State Exam or the Alzheimer’s Disease Assessment Scale.

Following this, the results of 8 clinical trials, involving 425 people, were then pooled for behaviour and neuropsychiatric symptoms, agitation and apathy. These results demonstrate a large positive effect of noradrenergic drugs on apathy, even after outliers were removed to account for differences in trial design and intended outcomes.

The researchers concluded: “Repurposing of established noradrenergic drugs is most likely to offer effective treatment in Alzheimer’s disease for general cognition and apathy,”

They continued: “There is a strong rationale for further, targeted clinical trials of noradrenergic treatments in Alzheimer’s disease.”

However, they did warn that several factors need to be considered first including appropriate targeting of particular groups of patients and understanding the dose effects of individual drugs and their interactions with other treatments to minimise the cons and maximise the pros of noradrenergic drugs.