SAMHSA's Office of Applied Studies released a Short Report based on the National Survey on Drug Use and Health that discusses substance use treatment need and receipt among people living in poverty.

From the report:

Combined 2006 to 2008 data indicate that 3.7 million persons aged 12 or older living in poverty were in need of substance use treatment in the past year.  Of these, 17.9 percent received treatment at a specialty facility during this time period.  Males living in poverty were nearly twice as likely as their female counterparts to need treatment in the past year (17.1 vs. 8.9 percent), but were only as likely as their female counterparts to have received treatment.  Among persons living in poverty, those aged 18 to 25 had the highest rate of past year treatment need; however, this age group had the lowest rate of treatment receipt. 

Full report: http://www.oas.samhsa.gov/2k10/173/173Poverty.cfm

U.S. Dept. of Health and Human Services. Substance Abuse and Mental Health Services Administration. (2010). The NSDUH report: substance use treatment need and receipt among people living in poverty.