Whether or not at-risk youth eschew illicit drugs because of its expected harm remains uncertain. In theory, expectancy is influential when the harm is valuable to the youth. Hence, to examine this possibility, this study employed a prospective design to collect data from 169 at-risk youths identified by social workers in Hong Kong, China.

Results revealed that when a youth has higher expectancy and valuation of harm in the baseline survey, he/she had considerably more drug-free days in the follow-up survey. However, neither the expectancy nor valuation alone introduced an effect on drug-free days.

These results sustained approaches to fostering the expectancy and valuation of harm for effective drug rehabilitation. Specifically, the approaches required to raise the expectancy of youth on the harm of drug abuse to their vigour and the value of sustaining their vigour simultaneously.