One of the suspects was apprehended while trying to flee the patrol in Kandahar province on Saturday, the military said in a statement.
The unit later investigated a camp near a "suspicious" mud hut and detained seven others. While at the site, the patrol seized the drugs, which the military only described as "narcotics."
Afghan border police arrived at the scene and confiscated the narcotics. Five of the detainees were transferred to the Afghan army. The other three were taken to a coalition base, the military said.
Afghanistan is the world's biggest producer of opium, the raw material of heroin. Last year, more than 4,500 tons of opium were harvested, about 90 percent of the global supply, the AP reports.
Some of the profits from the illicit business also are believed to go to militants allied with the Taliban, Afghanistan's former hard-line government that was toppled by U.S.-led airstrikes following the Sept. 11, 2001, terror attacks. Officials and police are also believed to benefit.
The U.S. government and other foreign donors have pumped hundreds of millions of dollars into fighting drugs in Afghanistan, but coalition forces are not normally involved in anti-drugs operations.