Health officials say synthetic marijuana has been linked to kidney damage in some teens and young adults.
Sixteen people who smoked synthetic marijuana were hospitalized with kidney problems last year in six states.
All recovered but five of them needed dialysis.
Synthetic marijuana is plant material sprayed with chemicals that can mimic the high from marijuana.
It's been tied to such health problems as a rapid heartbeat and seizures. This is the first report of kidney problems.
The Centers for Disease Control and Prevention said it's not known exactly what caused the kidney damage.
Federal and state laws ban some of the chemicals used for synthetic marijuana.
A CDC report Thursday details the 16 cases in Oregon, Wyoming, Kansas, Oklahoma, New York and Rhode Island.
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