Summary of characteristics of the 11 shortlisted social media platforms.

“Platform focus” gives a brief description of the primary usage of the platform. “Text data available” lists the types of text content that the platform contains, as determined by manual inspection of platforms. “Drug discussion not restricted” column has a checkmark if the platform does not restrict drug-related discussion, and an X if the platform has some form of restrictions, as determined by inspection of platform terms of use (provided in Appendix G in S1 Text). “Has API” column has a checkmark if the platform has an API available (whether the API is freely available or requires authorization before access), and an X if not. “Has research portal” column has a checkmark if the platform has a non-API platform for acquisition of platform data or to receive more information about collaboration with the platform, and an X if not. API and research portal designations were determined by inspection of platform data availability (provided in Appendix H in S1 Text). “Previously researched for opioid pharmacovigilance” column reflects the relative amount of prior research related to opioid surveillance, with a checkmark indicating some prior use in the literature, two checkmarks indicating high prior use in the literature, and an X indicating no prior use in the literature (see “Prior Use in Research Literature” section of Results). “Geolocation available” column has a checkmark if explicit geolocation data is provided for any platform content (this does not indicate explicit geolocation available for all content), and an X if not, as determined by inspection of public-facing platform data specifications (see “Evaluating data accessibility for academic research purposes” section of Results). “Example of geolocation inference strategy” column provides one possible method for inferring geolocation of platform content, based on inference strategies previously employed in the broader literature (see “Evaluating data accessibility for academic research purposes section” of Results).