Any regular duplicate drug class prescription, for example, two concurrent opiates, NSAIDs, SSRIs, loop diuretics, ACE inhibitors. Excludes duplicate prescribing of drugs that may be required on a p.r.n. basis, for example, inhaled β2 agonists (long and short acting) for asthma or COPD, and opiates for management of breakthrough pain. This evidence concerns the gene ACE and asthma.