SAN FRANCISCO (KGO) -- The use of fentanyl is going up and the medical community is trying to understand just what it does to the human body.
Things you may have witnessed are people so high, they just stand in the middle of the sidewalk bent over, appearing as if they were frozen in place.
The simple explanation:
"It's a degree of loss of consciousness and a degree of lost muscular control," said Dr. Daniel Ciccarone, a UCSF professor of addiction medicine.
But the effects of the opioid continue to linger on as the person continues with their daily life, in most cases awake but not able to stand up straight.
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We bumped into Andy Berger, who tried to explain his physical state at that moment. He told us he had used fentanyl earlier that morning, so it was still in his body. He was not able to straighten out.
"I mean, I can, but it hurts a lot to have to do that," he told us.
"Fentanyl can be a short-action drug and a long-acting drug. So some people they're back upright in 45 minutes to an hour. Some people could be longer than that," Ciccarone said.
He says fentanyl in long-term users takes time to clear out of the system because the drug tends to accumulate in the fat tissue.
The research community has yet to determine if fentanyl impacts the person's spine at all.
Berger told us he's more concerned about his swollen legs than his back.
"People's legs swell up and end up looking, getting sores," he said as he showed us his legs, which were in need of medical attention.
What researchers think might be happening there is that because the chemical is acidic, in some cases, it eventually makes veins collapse.
"I just didn't care about anything, drugs were my only driving force every day," said Ben Campofreda, once a heavy fentanyl user who weighed only 100 pounds when a spine infection sent him to the emergency room.
"I wore a hole in my leg from being in the wheelchair so long and that got infected, and the infection went into my spine," he said.
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Mind you, Campofreda had existing back issues. His pain is what drove him to addiction. The use of fentanyl made his condition even worse.
Because of that infection, UCSF surgeons had to remove two of his disks and two implants were inserted, providing more spacing between the vertebrae. This relieved the pressure on the nerves.
Campofreda now lives in Oregon and considers himself among the few able to get off fentanyl.
Earlier this year, he hiked the well-known Camino de Santiago de Compostela in Spain -- that's approximately 550 miles.
"My back is great. I'm in better shape than I've been since I was 20. I exercise every day. I stay very active. I'm very grateful to have that second chance at getting my life together," he said.
Campofreda acknowledges that the reason he is free of fentanyl is because he was hospitalized for his back, for months and months. He is grateful that he was.