Misuse of a powerful painkiller has spread like wildfire among schools in the west African state of Gabon, where teachers blame it for violent changes in mood among normally placid and motivated teenagers.
Known as "kobolo" by local youths, the drug comprises high doses of anti-inflammatory medicine, usually washed down with soda or alcohol. In the United States, abuse of such opioid drugs, say experts, has abetted a crisis of addiction and misery.
"It's easier to ask who in our state schools is not taking kobolo," said a young music teacher in a Libreville high school, who gave her name as Chantal.
"It starts at secondary level, from the age of 12 or 13. The children go through changes almost overnight -- they become aggressive and violent under the effects of kobolo, which we regularly find when we go through their schoolbags," she adds. "The worst thing is that the kids not only use it, they sell it, too."
Almost every week, the press report knife fights between pupils, largely blamed on their use of kobolo, and on arrests of drug dealers, often deemed to be connected to the pharmaceutical business or from Cameroon.
"Kobolo is a combination based on painkillers that act directly on the brain. It induces feelings of well-being due to the secretion of dopamine, the pleasure hormone," said Marie-Louise Rondi, who chairs the National Order of Pharmacists in Gabon.
"This explains addiction and the tendency to increase daily doses, until all the safety fuses in the brain have been blown."
When used by young Gabonese as a recreational drug, the painkiller Tramadol or a generic equivalent is taken in large doses, sometimes mixed with alcohol and a range of juices.
In 2017, its popularity began to spread fast in a country where consumption of cannabis and other substances is very limited.
By July, concern had become so great that prescriptions for the drug became compulsory, and social support was beefed up. "We had meetings with the parents of students to warn them of the scale of the problem," Rondi said.
Under the pseudonym Ted, a self-described "ex-user" of kobolo in his 20s, who comes from a poor neighbourhood, described what it was like to take the drug.
"With a soft drink, it's like you're asleep, having a waking dream. But if you drink it down with a little alcohol, well then...!" he guffawed.
"It awakens your sleeping senses, when you take it you become hot. You can't control yourself, you imagine you're a super-hero, you lose your feelings," laughs the young man. "It gives you too much courage... You don't even feel pain."
Proof of this risk, he displayed a large scar on a forearm -- the legacy of an accident when he "went through a car windscreen without feeling hurt."
Other collateral damage includes loss of appetite and sleep, itching, "epilepsy attacks, liver problems and and memory lapses," he said. Others say unsafe sex is another risk.
Despite regulatory efforts, the painkiller is easy to obtain on the streets of Libreville. Known as the "little red", "pink baby" or "kemeka," pills are sold for between 250 and 500 CFA francs (0.40 to 0.80 euros / $0.50 to $1.00) apiece.
Around the bus station, regular traders and ambulant salesmen help make acquiring kobolo a simple formality. In the maze of narrow streets, the drug is sold not only by the usual dealers but also at little stalls that sell medication along with rat poison.
For lack of official statistics, the kobolo business is difficult to put into figures. Since getting high requires no more than swallowing some cheap pills, the phenomenon is more discreet than smoking pot.
The wholesale dealers are above all Nigerians and Lebanese, Chadians and Guineans, people say in the working-class districts. "Everybody sells it under the counter," said Ted, who described kobolo as "the high-school favourite".
The media gives ample coverage to anti-kobolo operations and the police say they are on the job, reporting the seizure of 5,952 illicit pills in 2017.
"But the silence of health authorities is deafening," protests the director of a state-run hospital. "Not even a simple video clip on the TV to raise awareness among young people."
By contrast, "Goudronier," a video about kobolo by rapper Don'zer, has given the drug nationwide prominence. It has been even broadcast at meetings of political parties.
"What this song is about, with its words and the video full of violence, is what's happening now in our society and our schools," said the teacher Chantal, distraught.
"The drug has become fashionable -- kobolo users are no longer hiding."
Kobolo users are typically aged from 12 to 16 or 17, but there are many who come outside this age range, said a psychologist who has seen many users in her private practice.
"All social classes are affected, including the French and the Lebanese," she said, referring to two large expatriate communities.
The drug has increased the risk of unsafe sex and unwanted pregnancies for girls, the psychologist added.
"Me, I gave it up because of the violence, trouble with my parents," Ted said. "You laugh a lot, but it's not the right kind of laughter. And you lose friends who die in fights, getting stabbed or having their throats cut."