Cannabis concentrates are gaining rapid popularity in the California medical cannabis market. These extracts are increasingly being consumed via a new inhalation method called 'dabbing'. The act of consuming one dose is colloquially referred to as "doing a dab". This paper investigates cannabinoid transfer efficiency, chemical composition and contamination of concentrated cannabis extracts used for dabbing. The studied concentrates represent material available in the California medical cannabis market. Fifty seven (57) concentrate samples were screened for cannabinoid content and the presence of residual solvents or pesticides. Considerable residual solvent and pesticide contamination were found in these concentrates. Over 80% of the concentrate samples were contaminated in some form. THC max concentrations ranged from 23.7% to 75.9% with the exception of one outlier containing 2.7% THC and 47.7% CBD. Up to 40% of the theoretically available THC could be captured in the vapor stream of a dab during inhalation experiments. Dabbing offers immediate physiological relief to patients in need but may also be more prone to abuse by recreational users seeking a more rapid and intense physiological effect.