Intervention(s) and comparator(s)	Duration of intervention	Description of participants	Country	Setting	Ethnic groups (%)	Duration of diabetes (mean/range years (SD), or as reported)
Avilés 1999	I: metformin	24 weeks	Participants with poorly controlled type 2 diabetes on insulin therapy	USA	Secondary care outpatients	White: 49 African‐American: 23 Hispanic :23 Other: 5	9.2 (6.4)
	C: placebo					White: 68 African‐American: 18 Hispanic: 14	10.1 (4.7)
Barnett 2013	I: saxagliptin	52 weeks	Inadequately controlled type 2 diabetes individuals with insulin alone (subgroup in the publication)	Canada, Hungary, India, Mexico, Poland, Russia, South Africa, UK	Multiple choices possible	White: 84.2 Black: 6.3 Asian: 7.4 Other: 2.1	12.1 (6.3)
	C: placebo					White: 76.1 Black: 10.9 Asian: 6.5 Other: 6.5	10.3 (6.4)
Casner 1988	I: glibenclamide	12 months	Participants with type 2 diabetes on insulin therapy	USA	Unclear	Hispanic: 84 Non‐Hispanic white: 10 Non‐Hispanic black: 6	14.3 (0.1)
	C: placebo					Hispanic: 94 Non‐Hispanic white: 6	10.9 (0.1)
Chiasson 1994	I: acarbose	12 months	Participants with type 2 diabetes (26% pretreated with insulin, only results of this subgroup is used)	Canada	Secondary care outpatients	‐	‐
	C: placebo					‐	‐
	all:					White: 92	12.9 (0.8 SE)
Coniff 1995	I: acarbose	24 weeks	Insulin pretreated participants with type 2 diabetes	Canda, USA	Not stated	‐	‐
	C: placebo
Feinglos 1998	I: glipizide	3 months	Participants with type 2 diabetes taking insulin	USA	Secondary care inpatients and outpatients	‐
	C: placebo
	all:						15 (3 ‐ 30)
Fonseca 2007	I: vildagliptin	24 weeks	Participants with type 2 diabetes inadequately controlled by insulin	Finland, Germany, Spain, USA	Unclear	Black: 15 White: 70 Hispanic + Latino: 12 Other: 3	14.4 (8.6)
	C: placebo					Black: 11 White: 72 Hispanic + Latino: 15 Other: 2	14.9 (8.4)
Fritsche 2000	I: metformin	10 weeks	Severely obese participants with type 2 diabetes on intensified insulin therapy	Germany	Secondary care inpatients and outpatients	‐
	C: placebo
	all:					‐	10 (8)
Giugliano 1993	I: metformin	6 months	Obese type 2 diabetes on insulin therapy	Italy	Secondary care outpatients	‐	11.9 (1.2)
	C: placebo						11.5 (1.2)
Groop 1985	I: glibenclamide	8 weeks	Poorly controlled participants with type 2 diabetes on insulin	Finland	Secondary care outpatients	‐
	C: placebo
	all:						8 (1)
Hermann 2001	I: metformin	12 months	Overweight and obese type 2 diabetes participants on insulin therapy	Sweden	Secondary care outpatients	‐	13 (3 ‐ 31)
	C: placebo						13 (4 ‐ 25)
Hirsch 1999	I: metformin	5 months	Participants with type 2 diabetes and sub optimal insulin therapy	USA	Secondary care outpatients	‐	‐
	C: placebo					‐	‐
Hong 2012	I: Sitagliptin	24 weeks	Participants with uncontrolled type 2 diabetes on insulin therapy	Korea	Secondary care outpatients	‐	15.9 (10.5)
	C: insulin increase						15.8 (9.9)
Kitabchi 1987	I: tolazamide	3 months	Obese insulin‐requiring participants with type 2 diabetes	USA	Secondary care inpatients and outpatients	‐
	C: insulin alone
	all:						10 (1)
Krawczyk 2005	I: metformin	6 months	Obese insulin‐requiring participants with type 2 diabetes	Poland	Secondary care outpatients	‐	12.2 (4.8)
	C: insulin alone						11.9 (5.9)
Kyllastinen 1985	I: glibenclamide	2 months	Elderly participants with type 2 diabetes on insulin therapy	Finland	Secondary care outpatients	‐
	C: placebo
	all:						11 (1)
Lewitt 1989	I: glibenclamide	3 months	Insulin‐treated type 2 diabetes participants	Australia	Secondary care outpatients	‐	‐
	C: placebo
Lindström 1999	I: glibenclamide	3 months	Type 2 diabetes participants on insulin monotherapy	Sweden	Unclear	‐
	C: placebo
	all:						10.5 (1.2)
Longnecker 1986	I: tolazamide	8 weeks	Type 2 diabetes participants on insulin monotherapy	USA	Secondary care outpatients	‐
	C: placebo
	all:						12 (2)
Mattoo 2005	I: pioglitazone	6 months	Type 2 diabetes participants on insulin monotherapy	Australia, Belgium, Canada, New Zealand, Romania, Spain	Secondary care outpatients	White: 97	13.6 (6.8)
	C: placebo					White: 97	13.4 (6.1)
Mauerhoff 1986	I: glibenclamide	16 weeks	Type 2 diabetes participants on insulin monotherapy	Belgium	Secondary care outpatients	‐	11 (2)
	C: placebo						10 (2)
Mezitis 1992	I: glibenclamide	20 weeks	Type 2 diabetes participants on insulin monotherapy	USA	Secondary care outpatients	‐	‐
	C: placebo
Mudaliar 2010	I: pioglitazone	12 to 16 weeks	Type 2 diabetes participants on insulin monotherapy	USA	Clinical research centre	‐	‐
	C: placebo
Nemoto 2011	I: miglitol	24 weeks	Type 2 diabetes participants on insulin monotherapy	Japan	Secondary care outpatients	‐
	C: placebo
	all:						15.1 (8.5)
Osei 1984	I: glibenclamide	16 weeks	Type 2 diabetes participants on insulin monotherapy	USA	Secondary care inpatients and outpatients	‐	12.3 (1.2)
	C: placebo						12.9 (1.6)
Quartraro 1986	I: gliclazide	12 months	Type 2 diabetes participants on insulin monotherapy	Italy	Secondary care inpatients and outpatients	‐	12.1 (1.4 SE)
	C: insulin alone						11.8 (1.3 SE)
Reich 1987	I: glibenclamide	4 months	Type 2 diabetes participants on insulin monotherapy	USA	Secondary care inpatients and outpatients	‐	9.0 (3.1)
	C: placebo						9.7 (3.3)
Relimpio 1998	I: metformin	4 months	Type 2 diabetes participants on insulin monotherapy	Spain	Secondary care outpatients	‐	15.4 (7.7)
	C: insulin dose increase						15.3 (6.0)
Robinson 1998	I: metformin	12 weeks	Type 2 diabetes participants on insulin monotherapy	UK	Secondary care outpatients	‐	Study 1: 15 (7) Study 2: 14 (6)
	C: placebo
Rosenstock 2002	I1: pioglitazone 15 mg	16 weeks	Type 2 diabetes participants on insulin ± oral antidiabetic medication. Those participants on insulin + oral antidiabetic medication discontinued the oral drug at the beginning of the screening period. In addition the run‐in period for those participants was 6 weeks instead of 3 for the participants on insulin monotherapy.	USA	Unclear	White: 75	‐
	I2: pioglitazone 30 mg					White: 73	‐
	C1: placebo					White: 71	‐
Schade 1987	I: glibenclamide	16 weeks	Type 2 diabetes participants on insulin monotherapy	USA	Secondary care outpatients	‐	‐
	C: placebo						‐
	all:						10 (1)
Schiel 2007	I1: glimepiride	16 weeks	Type 2 diabetes participants on insulin monotherapy	Germany	Secondary care outpatients	‐	15.3 (8.4)
	I2: glimepiride + metformin						14.2 (8.0)
	C1: insulin alone						16.3 (6.7)
Simpson 1990	I: glipizide	8 weeks	Type 2 diabetes participants on insulin monotherapy	UK	Secondary care outpatients	‐	9 (2 ‐ 18)
	C: placebo						10 (1 ‐ 20)
Stenman 1988	I: glibenclamide	4 months	Type 2 diabetes participants on insulin monotherapy	Finland	Secondary care inpatients and outpatients	‐	‐
	C: placebo						‐
	all:						9.8 (4.7)
Strowig 2002	I1: metformin	4 months	Type 2 diabetes participants on insulin monotherapy	USA	Unclear	White: 52 Afro‐American: 15 Hispanic: 30 Other: 4	7.6 (4.1)
	I2: troglitazone					White: 57 Afro‐American: 17 Hispanic: 27	11.6 (6.8)
	C1: insulin alone					White: 55 Afro‐American: 29 Hispanic: 16	10.5 (7.3)
Wulffelé 2002	I: metformin	16 weeks	Type 2 diabetes participants on insulin monotherapy	The Netherlands	Secondary care outpatients	‐	14.0 (8.4)
	C1: placebo						12.0 (8.0)
Yilmaz 2007	I1: acarbose	6 months	Type 2 diabetes participants on insulin monotherapy	Turkey	Secondary care outpatients	‐	13.9 (7.2)
	I2: metformin						12.1 (7.7)
	I3: rosiglitazone						12.1 (7.9)
	C1: insulin alone
‐ denotes not reported C: comparator; I: intervention; SD: standard deviation; SE: standard error