The characteristics of the studies are reported in Additional file
1: Table S1. Three studies were conducted in the United States [
43‐
46] with the remainder in Norway [
47], Spain [
48], Jordan [
49] and the United Kingdom [
50]. Adherence to various medications were examined including (i) Theophylline [
43]; (ii) Prednisolone and β
2 agonists [
47]; (iii) Short and long-acting β
2 agonists, anticholinergic, methylxanthines, inhaled and oral corticosteroids [
48]; (iv) Short and long-acting β
2 agonists, long acting anti-cholinergic inhaled steroids, oral steroids, antibiotics [
49]; (v) Short and long-acting β
2 agonist, long acting anticholinergic, inhaled steroids, oral steroids [
50]; and (vi) Ipratropium bromide [
44,
45]. Medication adherence was the primary outcome in five studies (reported in six publications) [
43‐
47,
50], and a secondary outcome in two [
48,
49]. Outcomes were measured directly (blood serum ratios [
43], observation of inhaler technique [
48]) and indirectly (prescription refills [
43], Medication Adherence Scale [
48], Inhaler Adherence Scale [
48], Moriksy Scale [
46,
49,
50], inhaler device data [
44,
45], patient self-report [
44], pharmacy data [
47], canister weighing [
44] and tablet counts [
46]). Five studies assessed adherence using two or more measures [
43‐
48]. Brief counselling [
43], monitoring and feedback about medication use [
44,
45], and multi-component interventions were examined [
44‐
50]; delivered by pharmacists [
43,
46,
49,
50], general practitioners [
47], and a health educator [
44,
45]. Timing of outcome measures was relatively homogenous, with the majority involving a 6 and/or 12 month follow-up.