Data from Bulgaria's National Focal Point for Drugs and Drug Addiction shows a surge in deaths with confirmed fentanyl over the past three years.
In Plovdiv, drug prevention classes now reach younger children. Until now, experts at the Plovdiv municipal drug centre worked with pupils in grades 5 to 12, described as "middle school level".
Primary schools now regularly ask the experts for help, said psychologist Dobrina Yovcheva of the municipal drug council. "We also work with parents of children in grades 1 to 4. The age limit is falling," she said.
Fentanyl is spreading fast on the Bulgarian market. Psychologists call drug use "Russian roulette". Illegally sold medicines for depression also contain fentanyl.
"There are many stories from people who supposedly take Xanax, but feel strange and later find out it had fentanyl added," said Galya Dancheva, a psychologist at the municipal drug council and the prevention and information centre in Plovdiv.
Specialists say even a tiny amount of the drug can kill. Crystals the size of the tip of a very sharp pencil, similar to salt or sugar, are enough. They can cause an overdose, death or very serious harm.
Dancheva described the signs of poisoning. Less oxygen reaches the body and the so-called "wooden chest" sets in. The pupils become very narrow, "like pinpoints", speech is slurred, and the person vomits and feels dizzy.
On the streets of big cities, there are people who stand hunched over and helpless, and such cases are becoming more frequent in Plovdiv. Videos of them appear on social media every day.
One woman filmed such a group on Saedinenie Square. She said the people were not in their right mind. She was frightened and did not try to talk to them, because it was clear they could not answer.
In such a situation, specialists advise calling 112 immediately.