of cannabis develop behavioral and pharmacolo gical tolerance such that it can be difficult
to detect when they are under the influence. Signs of acute and chro nic use include red eyes
(conjunctival injection), cannabis odor on clot hing, yellowing of finger tips (from smoking
joints), chronic cough, burning of incense (to hide the odor), and exaggerated craving and
impulse for specific foods, sometimes at unusual times of the day or night. 
Prevalence 
Cannabinoids, especially cann abis, are the most widely us ed illicit psychoactive sub-
stances in the United States. The 12-month prevalence of ca nnabis use disorder (DSM-IV
abuse and dependence rates combined) is appr oximately 3.4% among 12- to 17-year-olds
and 1.5% among adults age 18 years and older.  Rates of cannabis use disorder are greater
among adult males (2.2%) than among adult females (0.8%) and among 12- to 17-year-old
males (3.8%) than among 12- to 17-year-old  females (3.0%). Twelve-month prevalence
rates of cannabis use disorder among adults decrease with age, with rates highest among
18- to 29-year-olds (4.4%) and lowest amon g individuals age 65 years and older (0.01%).
The high prevalence of cannabis use disord er likely reflects the much more widespread
use of cannabis relative to other illicit drug s rather than greater addictive potential. 
Ethnic and racial differences in prevalence are moderate. Twelve-month prevalences
of cannabis use disorder vary markedly across racial-ethnic subgroups in the United
States. For 12- to 17-year-olds, rates are hi ghest among Native American and Alaska Na-