Final answer:
It's not possible to accurately determine the least likely used drug by arrestees from the information provided, but given marijuana-related offenses are most common, marijuana would not be the least likely. Drug use trends and arrest rates vary greatly and are influenced by multiple factors.
Step-by-step explanation:
The drug or drug type that arrestees are least likely to have used, according to ADAM's (Arrestee Drug Abuse Monitoring) data, is not specifically mentioned in the provided reference material. However, given the context of the information, it can be deduced that marijuana-related offenses are the most numerous, suggesting that marijuana is not the least likely drug to have been used by arrestees. Additionally, the materials indicate a significant concern with the use and illegal distribution of prescription opioids as well as the historic heavy penalties associated with crack cocaine use.
It is imperative to note that drug use trends can vary significantly across different regions and over time. Arrest rates can be influenced by law enforcement practices, social attitudes, as well as the availability of various substances. Without the explicit data from ADAM or a reference to a direct comparison of all the listed drug types, it is not possible to accurately identify which drug arrestees are least likely to have used.