Sharing, group-buying, social supply, offline and online dealers: how users in a sample from six European countries procure New Psychoactive Substances (NPS) - Werse, B.; Benschop, A.; Kamphausen, G.; van Hout, M.-C.; Henriques, S.; Silva, J.; Dabrowska, K.; Wieczorek, L.; Bujalski, M.; Felvinczi, K.; Korf, D. (2019)