AimsYouth are frequently exposed to drugs, and most youth who misuse drugs are reluctant to seek help from services due to the worry of others being judgmental, lacking expertise, exposing their personal information, or informing their parents. Considering these concerns, we propose to evaluate the effectiveness of a medical peer-delivered intervention comprising brief motivational interviewing via instant-messaging interaction in reducing drug misuse among youth in Hong Kong.MethodsA two-group single-blind, randomised controlled trial will be conducted. Multiple approaches, including online and face-to-face methods, will be used to recruit the participants. The participants, aged 25 years or younger and reporting any drugs that they have taken within the past 30 days, will be recruited and randomised to receive either brief motivational interviewing via interactive instant-messaging (the intervention) or general health text-messages (comparator). The primary outcome will be the change in the participants’ reductions in self-reported drug consumption at 12 months compared to that at baseline. The secondary outcomes will be the changes in the drug-abusing participants’ reductions in self-reported drug consumption at 6 months, the changes in the drug-quitting participants’ 6- and 12-month contemplation stages and relapse risk compared to that at baseline, 30 days’ self-reported drug abstinence at 6 and 12 months, and the treatment needs and motivation at 6 and 12 months compared to that at baseline. The effectiveness of the proposed intervention will be examined with adjusted regression models, with adjustment for baseline characteristics and the use of an intention-to‐treat approach.DiscussionThis proposed study will be the first randomised controlled trial to assess the effectiveness of a medical peer-delivered interactive intervention to reduce drug misuse among youth in Hong Kong. The proposed intervention has the potential to increase the help-seeking behaviour and intention to quit among youth who misuse drugs. As a result, more youth misusing drugs may be helped to abstain from drugs. This proposed study will inform decisions on whether it is worthwhile to invest resources in large-scale implementation of such an intervention.