The agency said experts are analyzing samples to determine what toxin is causing problems. It has also asked doctors across the region to report cases of kidney failure that might be linked to the drug.
"This is not just a bad trip," said Gary Schnabel, executive director of the Oregon Board of Pharmacy, which voted to ban the sale and possession of synthetic cannabis products last year. "We are talking about your kidneys, and you only have two of them."
The six patients requiring hospitalization were from the Portland, Salem and Roseburg areas, as well as Vancouver, Wash. The most recent case occurred in late September.
Five of the patients were 18 or younger, and all were male. Though they have been discharged, they remain at heightened risk for kidney problems later in life.
Spice, which is typically smoked, is a mixture of plant material sprayed with a designer drug similar to THC, the main psychoactive component of cannabis. It's marketed under street names such as "K2," ''herbal incense" and "potpourri."
A University of Michigan study found that 11.4 percent of high school seniors reported using synthetic marijuana in the past year. There is no such statistic for Oregon.
The manufacturers are generally overseas and unknown, and there are often no ingredients on the package. The Oregon patients bought the illegal drug over-the-counter at places such as convenience stores, gas stations and tobacco shops, said Dr. Katrina Hedberg, the state epidemiologist.
Hedberg also told KATU News that doctors remain baffled about the chemical that is in the synthetic marijuana that causing the havoc.
"We don't have any good idea," she said. "It's a synthetic marijuana. It's composed of some sort of plant product. We don't know what the plant is, sprayed with some sort of chemical, and we don't know what that is. But it's similar to THC, which is the active ingredient in marijuana."
"It's very hard to regulate something that's being sold as potpourri," Hedberg told The Associated Press. "Doesn't that sound like something you put in your bathroom that smells nice?"
"It's a clear effort to circumvent the law," she added. "The people who are buying it know what it's intended use is while not explicit."
But law enforcement has taken notice. A federal grand jury in Idaho indicted five people in July on charges they conspired to distribute synthetic marijuana products. As part of the investigation, 14 search warrants were issued at businesses in Idaho, Oregon and southwestern Washington.
Meanwhile, authorities in Wyoming arrested three people in March after several users in the Casper area were hospitalized with kidney failure.
Poison centers nationwide responded to 3,200 calls related to synthetic marijuana or "bath salts" in 2010 and that number soared to more than 13,000 last year, said Jodie Underwood, Drug Enforcement Administration special agent in Seattle.
"A teenager thinks it safe because it's being sold in a gas station," Underwood said. "And these products are not for human consumption."
Dr. Sharon Su, a kidney specialist at Legacy Emanuel's Randall Children's Hospital, began treating a 17-year-old boy in August. (Read his firsthand account)
"His kidneys were shutting down," she told KATU News Friday.
The boy admitted he and four friends smoke synthetic marijuana. The boy was the only one of his friends who got sick.
"He was in really bad shape," Su said. "He did not eat for several days. He was in a lot of pain, which is really unusual for kidney failure."
Federal law enforcement does have a good lead on which batch of synthetic marijuana is tainted because of cooperation from the family of the boy Su treated.
"His father said, 'Tell me where it is, and I'll go buy it.' The next day he was able to buy it and bring it back."
Health officials are testing the synthetic marijuana to determine what the chemical is that's causing kidney failure.
Read firsthand account: 17-year-old boy warns of the dangers of 'spice'
- Washington State Department of Health: State permanently bans drugs such as Spice, K2 and "bath salts" (pdf)
KATU News reporter Dan Tilkin contributed to this report.