Speedballs often give stronger effects than either drug when taken alone due to drug synergy, and are a particularly hazardous mixture that can easily cause heart attack, respiratory arrest and death.[3] When compared to single drugs, speedballs are more likely to lead to addiction,[4][5] and users are more likely to relapse[4][6] and also to overdose.[7][8][9]
^Hunt, Dana E.; Lipton, Douglas S; Goldsmith, Douglas; Strug, David (1984). "Street pharmacology: Uses of cocaine and heroin in the treatment of addiction". Drug and Alcohol Dependence. 13 (4): 377. doi:10.1016/0376-8716(84)90005-X. PMID6479016.
^Wapler, M; Mendelson, J. H.; Teoj, S. K.; Mello, N. K.; Kuehnle, J. C.; Weiss, R. D.; Sholar, S. W.; Hanjra, B; Rhoades, E (1992). "Buprenorphine attenuates drug craving in men with concurrent heroin and cocaine dependence". Problems of Drug Dependence: 339.