The first dataset developed was for the CB8 host (Figure ). The host was previously featured in SAMPL3 and SAMPL6 , and is similar to other cucurbituril analogs such as CB7, CB-Clip , and TrimerTrip . The CB8 "drugs of abuse" challenge focuses on binding of CB8 to nine guests which are drugs of abuse, including morphine, hydromorphone, methamphetamine, cocaine, and others (Figure ). The list of guests on GitHub also includes cycloheptanamine and cyclooctanamine (G8 and G9); however, these were not part of the challenge since their experimental values were previously reported. Experimental binding affinities were measured by competition with these guests. CB[n]-guest complexes are well known to have very high affinity, especially for cationic ammonium and diammonium guests like those featured in SAMPL8. The high affinity measurements from these systems have been attributed to an enthalpic driving force provided by the lack of host hydrogen bonds with intracavity waters . Upon binding, protons of the guest's nitrogen interact with the oxygen of the CB8 carbonyl portal, which limits the number of poses that need to be considered computationally .