Synthetic marijuana products have been linked to a spiralling public health crisis in Illinois, where authorities say two people have died and dozens more have been hospitalised.

In dozens of cases that have rippled through the greater Chicago area in recent weeks, people have reported severe bleeding after using synthetic cannabinoid products, the Illinois Department of Public Health warned.

The toll has risen rapidly in recent days, climbing from 38 recorded incidents last week to 56. Nine of the afflicted have tested positive for a lethal ingredient often used as rat poison.

The agency has sent warning notices to emergency medical workers and local health departments around the state warning them to be alert. Noting that people sickened during the current outbreak have obtained the products from convenience stores and dealers, the department urged residents to not use any synthetic cannabinoids they’ve purchased in the last month.

Also referred to by names like “K2” and “spice”, synthetic cannabinoids are chemicals that mimic the effects of marijuana’s active components. But their effects are far less predictable and can include physical harm.

“Despite the perception that synthetic cannabinoids are safe and a legal alternative to marijuana, many are illegal and can cause severe illness”, Illinois Department of Public Health director Nirav Shah said in a statement. “The recent cases of severe bleeding are evidence of the harm synthetic cannabinoids can cause.”

Manufacturers are known to alter the chemical content to elude government prohibition, authorities say.

“Some of these substances may have been around for years but have reentered the market in altered chemical forms, or due to renewed popularity”, the Illinois health department said.

Even as states across the country have relaxed their laws governing marijuana usage, allowing people to possess the plant and its derivatives for medical and recreational purposes, a series of new laws have sought to crack down on synthetic marijuana.

Months before California voters approved recreational marijuana sales in 2016, for instance, Governor Jerry Brown signed a law expanding the state’s prohibition on synthetic cannabinoids to cover new chemical variations, following up on a 2011 law banning the products.