2. Details of intervention & comparator content & intensity.

Study ID	MI intervention description	Intervention intensity (no. of sessions; total duration)	Non‐MI comparator description	Comparator intensity	Intensity matched?	Pharmacotherapy used?	Other common intervention components
Ahluwalia 2006	MI counselling using semi‐structured script	6 sessions; 2 h	SC counselling providing information & advice to develop a quit plan	6 sessions; 2 h	Yes	NRT in half each condition; placebo NRT in other half	Tailored smoking cessation booklet
Audrain‐McGovern 2011	MET counselling	5 sessions; 3 h 15 min	Structured brief advice, using '5As' or '5Rs'	5 sessions; 1 h 15 min	No, comparator lower	n/a	n/a
Bastian 2013	MI & adaptive coping skills counselling + self‐directed materials. Skills training informed by Transactional Model of Stress & Coping	6 sessions; 3 h	Self‐help materials ‐ letter from oncologist encouraging quitting, quit kit (including SC guide), individually tailored booklet	n/a	No, comparator lower	NRT	Self‐help materials
Battaglia 2016	MI counselling + written SC information	12 sessions; 3 h 20 min	PTSD home telehealth programme + electronic (Health Buddy) device	n/a	No, comparator lower	NRT, bupropion or varenicline	PTSD home telehealth programme + electronic (Health Buddy) device
Bock 2008	MI counselling + self help resources	5 sessions; 1 h 20 min	Non‐MI counselling calls + self‐help resources	2 sessions; 20 min	No, comparator lower	NRT	2 brief non‐MI counselling calls, review of NRT use instructions
Bock 2014	MI counselling + 5As intervention	3 sessions; approx 1 h	5As intervention	1 session; 5 min	No, comparator lower	NRT	5As intervention
Butler 1999	Brief MI session	1 session; 10 min	Brief SC advice	1 session; 2 min	No, comparator lower	n/a	n/a
Catley 2016	MI counselling	4 sessions; length unclear	1. brief advice 2. SC counselling based on clinical guidelines	1. 1 session 2. 4 sessions (lengths unclear)	Yes (health education intensity matched) & No (brief advice ‐ lower)	NRT or varenicline	Self‐help guide
Colby 2005	MI counselling	2 sessions; 50 min	Brief recommendation to quit + follow‐up call	2 sessions; 10 min	No, comparator lower	n/a	SC pamphlet + treatment referrals information
Colby 2012	MI counselling. Participants' parents also discussed child's quit attempt and supporting it with researchers, using MI principles.	2 sessions for adolescents + 1 for parents; 1 h adolescents; 15 min parents	Brief SC advice with follow‐up session	2 sessions for adolescents; 10 min (none for parents)	No, comparator lower	n/a	SC pamphlet + treatment referrals information
Cook 2016	MI counselling	4 sessions; 50 min	1. Behavioural smoking reduction guidance 2. No treatment	1. 7 sessions; 1 h 20 min. 2. No sessions	1. No, higher 2. No, lower	NRT dependent on trial arm (balanced across arms of interest)	n/a
Davis 2011	Mi counselling	1 session; 15 min	Prescriptive interview regarding smoking ‐ firm & authoritative	1 session; 15 min	Yes	n/a	n/a
De Azevedo 2010	MI counselling	8 sessions; 1 h 40 min	Brief SC advice	1 session; 15 min	No, comparator lower	n/a	n/a
Demétrio Faustino‐Silva 2018	MI taught to SC advisors as additional resource to standard CBT approach used	Average 3 sessions; length unclear	Standard CBT approach advocated by Brazilian Ministry of Health's smoking programme	Average 3 sessions, length unclear	Yes	n/a	CBT counselling approach
Ellerbeck 2009	1. High intensity MI 2. Moderate intensity MI	1. 6 sessions every 6 min; length unclear 2. 2 sessions every 6 min; length unclear	n/a	n/a	n/a	NRT or bupropion	Welcome letter, information about medication, smoking cessation pamphlets, 6‐monthly personalised newsletter, periodic progress reports with counselling suggestions faxed to participants' physicians
Harris 2010	MI counselling	4 sessions; average 1 h 40 min	MI counselling focused on increasing fruit & vegetable consumption	4 sessions; average 1 h 40 min	n/a	Pharmacotherapy for highly dependent smokers	n/a
Helstrom 2007	MET counselling	1 session; length unclear	Information session on tobacco use based on American Cancer Society pamphlet	1 session; length unclear	Yes	n/a	n/a
Hollis 2007	1. high intensity MI 2. moderate intensity MI 3. low intensity MI	1. 5 sessions; at least 1 h 2. 2 sessions; at least 45 min 3. 1 session; 15 min	n/a	n/a	n/a	NRT for half of participants in each group	“Quit kit” including SC booklet
Kelly 2006	MI counselling	1 session; 1 h	SC counselling based on psychoeducation model	1 session; 1 h	Yes	n/a	Written materials
Lewis 1998	Brief motivational message to quit smoking, with follow‐up counselling incorporating CBT & MI	5 sessions; approx 1 h	Brief motivational message to quit smoking + SC pamphlet	1 session; 3 min	No, comparator lower	Placebo NRT	Brief motivational message to quit + SC pamphlet
Lloyd‐Richardson 2009	MET counselling	5 sessions; at least 2 h	Brief assessment of quitting plans with brief in‐person follow‐up	2 sessions; approx 10 m	No, comparator lower	NRT	n/a
Louwagie 2014	Brief MI session + short standardised SC message + SC booklet	1 session; 15‐20 min	Short standardised SC message + SC booklet	1 session; 1 min	No, comparator lower	n/a	Short SC message + SC booklet
Marshall 2016	MI counselling session + audio quit material + printed materials + quit‐line details	1 session; approx 25 min	Non‐tailored printed materials + quit‐line details	n/a	No, comparator lower	n/a	Written materials + quit‐line details
Matuszewski 2018	1. MI counselling + control intervention 2. MI counselling intervention + additional brief follow‐up	1. 1 session; average 10 min 2. 2 sessions; average 15 min	Referral to patient resource centre + quit‐line brochure	n/a	No, comparator lower	n/a	Referral to patient resource centre + quit‐line brochure
McClure 2005	MET counselling + control intervention	4 sessions; 1 h	Letter explaining association between cervical cancer & smoking + SC booklet + quit‐line details	n/a	No, comparator lower	NRT or bupropion	Letter explaining association between cervical cancer & smoking, SC booklet, quit‐line details
Naik 2014	MI counselling	not reported	No intervention (waiting list control)	n/a	n/a	n/a	n/a
NCT02645838	MI counselling	7 sessions; unclear‐ over 20 min	Brief SC advice	1 session; 5 min	No, comparator lower	n/a	n/a
Okuyemi 2013	MI SC and NRT adherence counselling	6 sessions; average 1h 45 min	Brief smoking cessation advice + SC guide	1 session; 10‐15 min	No, control lower	NRT	SC guide
Rohsenow 2014	1. MI counselling session 2. MI counselling session + booster sessions	1. 1 session; 45 min 2. 3 sessions 1h 5min	1. Brief advice using US AHRQ method 2. Brief advice + 2 booster sessions	1. 1 session; 15 min 2. 3 sessions; 35 min	No, comparator lower	NRT	SC pamphlets, information on SC skills groups & hard candy
Rohsenow 2015	MI session + booster sessions (half received non contingent payments & half contingent payments)	4 sessions; approx 2 h	Brief advice using US AHRQ methods (half received non contingent payments & half contingent payments)	4 sessions; approx 55 min	No, comparator lower	NRT	SC pamphlets & hard candy
Sherman 2016	1. MI & Problem Solving Therapy counselling 2. Referral to state Quitline (usually New York state) ‐ counsellors trained in MI	1. 7 sessions; approx 1 h 30 min 2. 2 sessions; approx 30 min	n/a	n/a	n/a	NRT	n/a
Soria 2006	MI counselling	3 sessions; 60 min	Brief anti‐smoking advice	1 session; 3 min	No, comparator lower	Bupropion for highly dependent smokers	n/a
Stein 2006	MI counselling	3 sessions; approx 1h	Brief advice using 4As + self‐help materials	2 sessions; approx 5 min	No, comparator lower	NRT	n/a
Tevyaw 2009	MET (half received non contingent payments & half contingent payments)	3 sessions; 2 h	Progressive muscle relaxation training (half received non contingent payments & half contingent payments)	3 sessions; 2 h	n/a	n/a	n/a
Vidrine 2019	1. Brief advice + text messages based on CBT & MI 2. Brief advice + texts + counselling calls based on CBT & MI	1. 1 session; approx 5 min. 2. 11 sessions; approx 2 h	Brief SC advice	1 session; approx 5 min	No, comparator lower	NRT	Brief quitting advice, written materials, quit‐line details
Woodruff 2007	Online virtual world (The Breathing Room) ‐ participants' avatars had MI group counselling with other participants & the counsellor within a virtual shopping mall setting	7 sessions; 5 h 15 min	No treatment	n/a	n/a	n/a	n/a
Wu 2009	MI counselling + SC self‐help materials	4 sessions; 4 h	Health education counselling + self‐help materials covering nutrition, exercise, and tobacco use	4 sessions; 4 h	Yes	NRT	n/a

^{5As: 'Ask, Advise, Assess, Assist, and Arrange'}

^{5Rs: 'Relevance, Risks, Rewards, Roadblocks, Repetition'
 AHRQ: Agency for Healthcare Research and Quality
 approx: approximately
 CBT: Cognitive Behavioural Therapy
 h: hour(s)}

^{m: month(s)
 min: minute(s)
 MI: Motivational interviewing
 MET: Motivational Enhancement Therapy
 n/a: not applicable
 NRT:nicotine replacement therapy
 PTSD: post traumatic stress disorder
 SC: smoking cessation}