Doctors were mystified when an 18-year-old French woman appeared at a hospital with scaly skin on her legs and hands, and was unsteady and mentally sluggish.
They were even more confused as her twin sister displayed similar, but less severe, symptoms and there was no family history of such a problem.
But several days later, doctors discovered the cause when a bag of mothballs was found stashed in her hospital room.
It seems the teenagers had been using the mothballs to get high by inhaling air from the bag for about 10 minutes a day because classmates had recommended it.
The sicker of the young women also had been chewing half a mothball a day for two months and took six months to fully recover.
Her twin, who had only been "bagging" for a few weeks, recovered after three months.
The doctors described the high as "dangerous" and likely to be the most under-reported in medical literature.
Doctors at the Hospital of Timone in Marseille, France say the teenager continued to use the mothballs during her hospitalization "because she thought her symptoms were not related to her habit.
Mothballs contain paradichlorobenzene (PDB) which is used to prevent moth larva from getting into clothing; the substance is also found in air fresheners and insect repellents and when abused can cause liver and kidney failure, and severe anemia.
Experts say teenagers are increasingly experimenting with legal drugs such as OxyContin, widely known as "hillbilly heroin," and Vicodin, often bought online or taken from medicine cabinets, even before trying marijuana or alcohol.