Justices on Thursday rejected the challenge by a coalition of conservative groups who had asked the court to block the proposed measure from the November ballot. 

The measure would allow patients with qualifying conditions to buy marijuana from nonprofit dispensaries with a doctor's recommendation. 

The proposal acknowledges that marijuana is still illegal under federal law, but its opponents argued that it doesn't adequately explain that users could face federal prosecution. 

Arkansas will be the first Southern state to put the medical marijuana issue to voters. Seventeen states and the District of Columbia have legalized it in some fashion.

(Copyright 2012 by The Associated Press. All Rights Reserved.)