An American man almost died after psychedelic mushrooms started growing in his veins after he injected them into himself.

The 30-year-old patient survived but he suffered liver damage, kidney failure, jaundice, diarrhoea, fatigue, nausea and vomiting blood.

It took doctors in a Nebraska hospital a series of tests to figure out what was wrong with the man since he was too confused to answer questions.

According to a case report published in the Journal of the Academy of Consultation-Liaison Psychiatry, the man had reduced the magic mushrooms into fine particles, made them into tea, and then injected it into his body.

Then the fungus began to sprout in his bloodstream.

He injected the psychedelic instead of following his usual schedule of medications for dealing with bipolar disorder.

He was in the hospital for 22 after being placed on a ventilator when he went into septic shock and acute respiratory failure.

However, he will have to remain on antibiotics and antifungals to stop the fungus from sprouting again in his bloodstream.

"The case reported above underscores the need for ongoing public education regarding the dangers attendant to the use of this, and other drugs, in ways other than they are prescribed," read the study.

Psychedelic mushrooms contain psilocybin, a chemical that is responsible for causing hallucinations on ingestion. When used as a drug it has shown to cause euphoria and is being researched as a potential treatment for depression and anxiety.

But a "bad trip" on psilocybin can result in panic attacks, suicidal thoughts, psychosis, violent behaviour, and convulsions.