In 2006, 23.6 million persons aged 12 or older needed treatment for an illicit drug or alcohol use problem (9.6 percent of the persons aged 12 or older). Of these, 2.5 million (10.8 percent of those who needed treatment) received treatment at a specialty facility. Thus, 21.2 million persons (8.6 percent of the population aged 12 or older) needed treatment for an illicit drug or alcohol use problem but did not receive it. These estimates are similar to the estimates for 2005.*  see the rest of the NIDA article here