Recent studies have linked hayfever medication with decreased brain size and slower metabolism. Last year, a US study found that taking a daily dose of medications like Clarityn or Piriton for three years or more increased the risk of developing alzheimer's disease by 60%. However, the reasons for the links were unclear and those suffering with allergies were advised to continue taking their medications. Now researchers at Indiana University School of Medicine believe they have found the reason between the link, as well as some other nasty side effects that come with taking hayfever medication. Spotted on The Telegraph, it has been found that the drugs work by blocking acetylcholine, a chemical involved in the transmission of electrical impulses between nerve cells. People diagnosed with alzheimers often lack acetylcholine, meaning that hayfever meds could indeed trigger or exacerbate the condition. In the new study, people who had taken the pills continually for over two years were found to have smaller brains and slower metabolisms, and also scored worse in memory and cognitive tests. Author of the paper,  Dr Shannon Risacher said: "These findings provide us with a much better understanding of how this class of drugs may act upon the brain in ways that might raise the risk of cognitive impairment and dementia. “These findings might give us clues to the biological basis for the cognitive problems associated with anticholinergic drugs. "Given all the research evidence, physicians might want to consider alternatives to anticholinergic medications if available when working with their older patients.”