Twenty-two people have been hospitalized with bleeding from the eyes and ears after using synthetic pot, Illinois health officials have said.

This is the first time that severe bleeding has been associated with the drugs known as cannabinoids, a mix of hundreds of chemicals that act on the same brain cell receptors as the active ingredient in marijuana.

Known as 'fake weed', 'K2' or 'spice', synthetic pot has been known to create a 'zombie-like' psychotic effect with extreme anxiety, paranoia and hallucinations.

Hundreds of people across the US have been hospitalized or killed as a result of synthetic pot in recent years as health officials struggle to regulate the substance.

The Illinois Department of Public Health issued a warning Tuesday about synthetic marijuana after 22 users visited the hospital with severe bleeding from the eyes and ears in recent weeks

The Illinois Department of Public Health (IDPH) issued a statement Tuesday warning anyone who experiences bleeding or bruising after using synthetic marijuana to seek medical attention.

At least four of the 22 cases were attributed to vitamin K-dependent coagulopathy, a condition that reduces the blood's ability to coagulate because of a vitamin K deficiency.

The condition has previously been linked to rat poisoning and is more commonly found in animals than in humans.

Melaney Arnold, a spokesperson for the IDPH, told the Chicago Tribune this new symptom could be a result of a change in chemical formula, but it is difficult to tell without knowing the exact makeup of the products.

Arnold said manufacturers could be tweaking the recipe for these products to get around a statewide ban and allow them to be sold legally.

What is synthetic cannabis? Synthetic marijuana contains man-made chemicals that act on the same cell receptors in the brain as THC does in natural marijuana. Manufacturers first started to sell synthetic pot in the early 2000s, marketing them as 'safe' alternatives to marijuana that do not show up on drug tests. They consist of a mix of plant material - herbs or spices, hence the name - that have been sprayed with chemicals to mimic the effects of marijuana and other cannabinoids. But often, the chemicals have drastically different and dangerous effects. Spice and K2 can cause seizures, nausea, vomiting, high blood pressure and erratic and even violent behavior. Advertisement

The people who were admitted to the hospital with bleeding eyes and ears admitted to having used synthetic pot, but it is unclear what their source was.

Most of the cases were reported in the Chicago area but officials warn contaminated products could be available throughout the state.

'Despite the perception that synthetic cannabinoids are safe and a legal alternative to marijuana, many are illegal and can cause severe illness,' Dr Nirav Shah, IDPH director, said.

'The recent cases of severe bleeding are evidence of the harm synthetic cannabinoids can cause.'

The health effects of using synthetic cannabinoids can be unpredictable, dangerous and possibly life-threatening because it's difficult to know what's in them or how a person will be react to them.

Previous studies have linked the drugs to symptoms including seizures, vomiting, chest pain, cardiac problems, kidney damage and brain damage.

Since 2015 hundreds of people across the US have overdosed and been hospitalized after smoking too much or bad batches of synthetic cannabis.

K2 was long sold in corner stores, wrapped in bright packaging and bearing a 'not for human consumption' stamp.

Government agencies are finally beginning to crack down on the unregulated substance.