1. Baseline characteristics of included studies in all randomized participants aged 18 years or older.

Study Study design	Number of 18‐ to 59‐year‐old participants/total randomized participants (%) Characteristics of all randomized participants in each study	Mean baseline SBP/DBP (mmHg)	Mean age (range)	Control group	Treatment used	Outcomes reported in 18‐ to 59‐year‐old participants
Carter 1970 Open label	49/97 (50.5%); included all hypertensive survivors aged < 80 years of ischaemic type major strokes admitted to Ashford Hospital. Men: 57%	165/101	Not reported (40 to 79 years)	Untreated	Stepped‐up therapy Bendrofluazide (93%), methyldopa and debrisoquine FU 4.0 years	All‐cause mortality
HSCSG 1974 Double blind	252/452 (55.7%). 80% of participants had completed stroke in year before randomization; 16% completed stroke + TIA and 4% TIA only. Severe neurological disability in 9.9% of treated group and 5% of control group. Black: 80% Men: 60%	167/100 77% of the drug treated and 74% of the placebo treated participants had SBP < 180 mmHg	59 years (< 75 years)	Placebo	Fixed‐dose therapy Deserpidine 1 mg + methyclothiazide 10 mg FU 3.0 years	Cardiovascular mortality + morbidity Cerebrovascular mortality + morbidity CHD mortality + morbidity
MRC‐TMH 1985 Single blind	14,541/17,354 (83.8%). Men: 52%. Primary prevention participants. Refer to exclusion criteria listed in Characteristics of included studies table.	161/98.	52 years (35‐64 years)	Placebo 288/12,375 (0.02%) participants randomly assigned to observation taking no tablets and merged with placebo	Stepped‐up therapy Bendrofluazide 10 mg daily (71% monotherapy), propranolol 80‐240 mg daily (78% monotherapy), methyldopa added if required FU 4.9 years	All‐cause mortality Cardiovascular mortality + morbidity Cerebrovascular mortality + morbidity CHD mortality + morbidity SBP DBP
Oslo 1986 Open label	785/785 (100%) Men: 100% Primary prevention participants. Refer to exclusion criteria listed in Characteristics of included studies table	156/97	45 years (40‐49 years)	Untreated	Stepped‐up therapy Hydrochlorothiazide (95%), methyldopa and propranolol (26%). At 5‐year follow‐up, 36.7% were on hydrochlorothiazide alone, 26% were on hydrochlorothiazide + propranolol, 20% were on hydrochlorothiazide + methyldopa and 18% participants were on other drugs. FU 5.5 years	All‐cause mortality Cardiovascular mortality + morbidity Cerebrovascular mortality + morbidity CHD mortality + morbidity SBP DBP
USPHSHCSG 1977 Double blind	389/389 (100%) Men: 80% Primary prevention participants. Refer to exclusion criteria listed in Characteristics of included studies table	147/99	44 years (21‐55 years)	Placebo	Fixed‐dose therapy Chlorothiazide 500 mg twice daily + Rauwolfia serpentina 100 mg twice daily FU 7.0 years	All‐cause mortality Cardiovascular mortality + morbidity Cerebrovascular mortality + morbidity CHD mortality + morbidity SBP DBP
VA‐II 1970 Double blind	299/380 (78.7%) Men: 100% Primary prevention participants. Refer to exclusion criteria listed in Characteristics of included studies table	176/103	51 years (range not reported)	Placebo	Stepped‐up therapy First line: hydrochlorothiazide 100 mg + reserpine 0.2 mg Second line: hydralazine 75‐150 mg FU 3.3 years	Cardiovascular mortality + morbidity Cerebrovascular mortality + morbidity CHD mortality + morbidity
VA‐NHLBI 1977 Double blind	1012/1012 (100%) Men: 100% Primary prevention participants. Refer to exclusion criteria listed in Characteristics of included studies table	SBP not reported/93	38 years (range 21‐50 years)	Placebo	Stepped‐up therapy Chlorthalidone 50 mg, 100 mg (53% chlorthalidone alone) Reserpine 0.25 mg FU 1.5 years	All‐cause mortality Cardiovascular mortality + morbidity Cerebrovascular mortality + morbidity CHD mortality + morbidity DBP
Total of 7 studies published from 1970 to 1986	17,327/19,684 (88% of total randomized participants in the 7 studies were 18‐59 years of age) of which only 301/1,7327 (0.02%) participants were secondary prevention	SBP 147‐176/DBP 99‐103 mmHg	Mean age 37.5‐45 years	5 RCTs were placebo controlled and 2 RCTS had untreated group as control	Mostly high‐dose thiazide and beta‐blockers Mean follow‐up 1.5‐7 years.	5/7 RCTs report on all clinically important outcomes

CHD: coronary heart disease; DBP: diastolic blood pressure; FU: follow‐up; SBP: systolic blood pressure; TIA: transient ischaemic attack.