Collecting real-time data from substance users raises unique legal and ethical issues: reply to Kuntsche & Labhart

Kuntsche Labhart advocate using smartphones to collect real-time data on substance use so as to reduce biases inherent in `pen-and-paper diary methods? and retrospective studies [1]. They argue that `the main limitation for a more intensive use of this technology in the area of substance use is researchers? hesitation?. However, smartphones raise nascent legal and ethical issues to be addressed if we are to realize their potential as both a research tool and clinical device for illicit drug users. Foremost among these is the protection of participants? privacy and the legal risks associated with collecting potentially incriminating data. Data collected by researchers on illegal drug use and other activities can be subpoenaed by law enforcement agencies in most countries