Fingers bloodied, a man tried to dig through concrete with his bare hands because he thought someone was trying to bury him, while another kept hitting his head with an ashtray.

These were scenes at parties that once played out in front of a former LSD user, who wanted to be known as Mr Tan.

The former gang member said reality disappears when a person uses lysergic acid diethylamide, or LSD.

The substance is a potent hallucinogen and a Class A controlled drug listed under the Misuse of Drugs Act.

Mr Tan said that in his experience, the drug often came as little pieces of blotting paper, also known as LSD stamps.

LSD users describe the experience of taking the drug as a "trip".

"For a few hours, you're just a passenger at the mercy of where the trip takes you," said Mr Tan.

The 35-year-old, who was once involved in gang and drug activities, has spent seven years behind bars. He was first sent to the Singapore Boys' Home for rioting at age 13.

He started substance abuse at a young age, inhaling glue before moving on to taking heroin, another Class A controlled drug, and then LSD.

When he was introduced to LSD at 23, he thought his friend was trying to play a prank on him. Like most people, Mr Tan had not heard of LSD before.

He was given a stamp with a heart-shaped logo.

Of his experience in taking the drug, Mr Tan, a father of two young daughters, said: "Nothing made sense.

"When I touched a glass panel, I could feel its heat, and sometimes its smooth surface would poke my fingertips. I realised later it was all my imagination."

The drug, which came in sheets of 20 stamps each, was usually consumed at parties with close friends.

On one occasion, a female acquaintance jumped into a swimming pool thinking she was escaping a tsunami.

"We all laughed at first," said Mr Tan. "That's because the part of the pool she thought was 2m deep was only ankle deep.

"But she was seriously hurt from diving in head first."

Out of fear, the rest of them fled.

By the time Mr Tan was in his mid-20s, he had left the life of drugs and gangs.

He said it was akin to having "one foot in prison and the other in the grave".