Background About half of the daily smokers in Hong Kong have never tried and have no intention to quit smoking. 37.9% of daily smokers attempted to quit but failed. Nicotine replacement therapy (NRT) is a safe and effective pharmacotherapy to reduce withdrawal symptoms during early stage of tobacco abstinence and increase quit rate. However, the prevalence of using NRT in Hong Kong is lower than most of the developed countries. The proposed project aims to test if providing free NRT sampling to smokers can increase quit attempt and hence quit successfully.

Methods Nurses and university undergraduate students will be trained, and will invite smokers at outdoor public places to participate in the randomized controlled trial, which randomized eligible smokers to intervention or control group. The intervention group will be provided with 1-week free NRT sampling and medication counselling, whereas the control group will only be advised to purchase NRT on their own. The primary outcome is the proportion of any self-reported quit attempt (no smoking for at least 24 hours) in the past month at 1- and 3-month telephone follow-up.

Discussions The findings will inform the feasibility and effectiveness of delivering free NRT sampling to increase quit attempt and abstinence. It will yield more information on smokers' adherence to the NRT sampling, side effect and safety issue of the usage. Moreover, it will guide a future larger trial to test the effect from the NRT sampling and translation to practice.

Trial design The study aims at motivating smokers to have quit attempt using nicotine replacement therapy (NRT) sampling. We will firstly train nurses and university undergraduate students as outreach smoking cessation ambassadors. These trained ambassadors will proactively approach the smokers at outdoor smoking hotspots, where rubbish bins with a collector of cigarette butts are nearby, and invite them to participate in the RCT.

Subjects Smokers with the following inclusion criteria will be invited to participate in our RCT: (1) Aged 18 years or above; (2) Smoke 10 cigarettes or more per day in the past week; (3) Able to read and speak Chinese; (4) Have not used NRT for the past 3 months; (5) Have no severe angina and serious cardiac arrhythmias; (6) Have not suffered from acute myocardial event in the past 4 weeks; and (7) Not pregnant and breastfeeding The recruitments of subjects will take place at 9 outdoor urban places where smokers stayed and smoked from July 2015 to September 2015 (To be confirmed) Procedures We target to train nurses and smoking cessation ambassadors for the recruitment and providing intervention to the subjects. Recruitment of outreach smoking cessation ambassadors will be conducted through sending mass mails to students of the University of Hong Kong. Retired nurses who are now providing counselling services in our existing smoking cessation projects will be recruited. They will be invited to participate in a training programme which provides them an overview of the smoking cessation counselling and pharmacotherapy in helping smokers quit smoking. Our research team (comprised of physicians and nurses) will develop the training material and intervention guide based on the principles of the US Agency for Health Care Policy and Research (AHCPR) guidelines in the US [28], the guidelines of the National Institutes of Health [29] and World Health Organization [30]. The training content will cover (1) smoking trend in Hong Kong; (2) health hazards of smoking, (3) basic skills in assessing smoking dependence and quitting readiness; (4) knowledge of smoking cessation medication (types of NRT, adherence and side effects etc.) and (5) brief counseling skills. At the end of the training, participants should be capable of delivering brief intervention of smoking cessation including the advice on using NRT.

Smoking cessation ambassadors will approach the smokers and distribute souvenirs with smoking cessation messages at the outdoor smoking hotspots. The souvenir will be a small pack of tissue paper, with motivational messages (e.g. 1 in 2 smokers will be killed by smoking), quitline number (e.g. Quitline of Tobacco Control Office 1833183) and other resources for quitting printed on the tissue pack. If the smoker is willing to accept the souvenir and talk to the ambassador, the ambassador will ask further questions related to the eligibility through an informal conversation. If the subject is eligible, the ambassador will seek his/her consent to receive further intervention and provide his/her mobile phone number.

Interventions The intervention group will receive a free pack of one-week NRT. The nurse will help the subject to decide which NRT product (patch, gum and lozenge) he/she can use and advise how to use the NRT based on his/her smoking habit and amount of cigarette consumption, followed by the delivery of the sampling, instructions of using the NRT sampling, an education card about NRT and a 12-page smoking cessation booklet (Figure 1). Based on the experience in the previous trials, the choice of NRT (either patch, lozenge or gum) will be made according to subject's preference, and the counsellors will provide medication counselling [25-27]. If the subject is willing to continue the counselling at recruitment, the ambassador will further introduce the NRT's side effects, adherence and effectiveness (Table 1). Otherwise, the ambassador will contact the subject for providing these details and enquiring the usage through telephone within 2 days.

Some subjects may not be interested to use NRT sampling or some may not use them for quitting it. An envelope with a return address and pre-paid postage will be given with the NRT sampling, so that subjects can send back any unused NRT sampling to us to avoid wastage.

The control group subjects will only be advised by the ambassador to purchase the NRT on their own, but will not be given the sampling. The same education card and the 12-page smoking cessation booklet will be provided.

Outcomes The primary outcome of the RCT is the proportion of any self-reported quit attempt (no smoking for at least 24 hours) in the past month at the 1- and 3-month follow-up. The secondary outcomes are (1) self-reported 7-day point prevalence of abstinence at 1-, 3- and 6-month follow-up; (2) perceived importance, confidence and difficulty to quit (scale 0-10) at all the follow-ups; (3) proportion of using all free NRT samples; (4) biochemically validated abstinence at 1-month follow-up.

At 1 week, 1, 3 and 6 months after the recruitment, all subjects will be contacted by a trained interviewer via telephone to assess their smoking status and discuss any difficulties they might have encountered. At least 7 call attempts at different time will be made before the subject is considered as loss to follow-up. Subjects who report no smoking in the past 7 days will be considered as self-reported quitters. Self-reported quitters at 1 month will be invited to participate in a biochemical validation including measurement of exhaled carbon monoxide (CO) and salivary cotinine level by NicAlert® strips (www.nymox.com). The criteria for validated abstinence were exhaled CO < 4 ppm and salivary cotinine < 10ng/ml [31, 32].

Sample size determination Since the RCT will test the feasibility and generate preliminary estimates of effectiveness of the NRT sampling, we propose the sample size as 50 for each arm (i.e. total sample size = 100). A similar RCT conducted by Jardin et al. (2014) which evaluated the effectiveness of 2-week free NRT to help non-motivated smokers to quit smoking was chosen for the power estimation. The results showed that the 3-month quit attempt rate of receiving free NRT was significantly higher than those who only received a quitline referral only (32% vs 16%, p=0.05). The relative risk (RR) is therefore determined (32%/16% = 2.0). Based on the RR of 2.0, and the 100 subjects, the power and type I error for detecting the difference using the Fisher's exact test will be 69.7% and 0.08.

Randomization Sequentially numbered, opaque sealed envelopes (SNOSE) and block randomization will be used to allocate subjects into two RCT groups. The primary investigator will prepare 100 identical, opaque, sealed, A5-sized envelops. 50 of them will each contain an eligibility form, an education card of NRT, an action plan for the intervention group, and an empty box of NRT. The other 50 envelops will contain the same eligibility form and education card, and an action plan for the control group. The ambassador will create a block of 4 envelops, with 2 in the intervention group and 2 in the control, and shuffle them thoroughly and contain them in a separate pile. Recruitment staff will use 1 of the 25 piles of the envelopes and randomly select 1 envelope for the intervention.

Allocation concealment The group allocations were concealed to the subjects and the ambassador. Subjects will not be aware of the allocation throughout the study.

Blinding As the assessors of the outcomes will be blinded to the group allocation, this RCT will be single-blinded.

Data analyses All data will be entered and analyzed with SPSS for Windows version 20. The rate of quit attempt and 7-day abstinence will be assessed with t-test and odds ratio from logistic regression. Both intention-to-treat (assuming missing subjects have no changes) and complete case analysis will be done.

Ethics NRT for smoking cessation was proved as an effective and safe aid to smoking cessation, which can be purchased over-the-counter in pharmacy or freely prescribed in the smoking cessation clinics in Hong Kong. Common side effect of nicotine patch is skin reaction. About 50% of patients using the nicotine patch will experience a local skin reaction. The reaction is usually mild and self-limiting, but occasionally worsens over the course of therapy. Local treatment with hydrocortisone cream (1%) or triamcinolone cream (0.5%) and rotating patch sites may ameliorate such local reaction. In fewer than 5% of patients, such reaction requires the discontinuation of the NRT. Other side effects are insomnia and/or vivid dreams. Common side effects of nicotine gum include mouth soreness, hiccups, dyspepsia, and jaw ache. These effects are generally mild and transient and often can be alleviated by correcting the patient's chewing technique. [10] These effects are generally mild and can be alleviated by correcting the patient's using habit. All subjects will be asked at the first 7-day telephone follow-up if they have the above side effects. If so, the counsellor will provide counselling on the usage. If the side effects are serious, counsellor will ask them to cease the usage and mail back the sampling.

Inclusion criteria:

1. Aged 18 years or above;
2. Smoke 10 cigarettes or more per day in the past week;
3. Able to read and speak Chinese;
4. Have not used NRT for the past 3 months

Exclusion criteria:

1. Have severe angina and serious cardiac arrhythmias;
2. Have suffered from acute myocardial event in the past 4 weeks;
3. Pregnant and breastfeeding