Use of the drug K2, which can lead to erratic behavior and unpredictable side effects, is on the rise in Philadelphia, cropping up in neighborhoods like Kensington, the heart of the city’s opioid epidemic, and at Suburban Station, where officials say it is contributing to a tense relationship between police and people who shelter there.

Twice in two months, SEPTA transit police have come under scrutiny for their interactions with homeless people, including a clash in January that turned violent, in which officers sprayed people with mace and hit them with batons. These incidents prompted an outcry from advocates for vulnerable people who often suffer from serious mental health and addiction issues. Blossoming use of K2 — a synthetic compound sprayed on plant matter and smoked — is making the situation more volatile, they say.

“What’s happening in Suburban Station right now is very different than what was happening three years ago,” said Sister Mary Scullion, executive director of the homeless support nonprofit Project HOME. The big problem is addiction, she said, and K2 is exacerbating the problem.

Transit officers described some people acting almost unresponsive, while others become wild, as if they had taken PCP. K2 is a lab-made cannabinoid that acts on the same brain receptors as marijuana, but has far more unpredictable effects, which can include catatonia, psychosis, and agitation that can lead to violence.