Exploring Perceptions About Paracetamol, Tramadol, and Codeine on Twitter Using Machine Learning: Quantitative and Qualitative Observational Study - Carabot, F.; Donat-Vargas, C.; Santoma-Vilaclara, J.; Ortega, M.A.; García-Montero, C.; Fraile-Martínez, O.; Zaragoza, C.; Monserrat, J.; Alvarez-Mon, M.; Alvarez-Mon, M.A. (Journal of medical Internet research, 2023)