Mixing cocaine and alcohol together creates a "deadly combination" which can increase violent and impulsive behaviour, doctors are warning.
At least 13 "self-inflicted" deaths happened in a year in England among people who took the two substances, the Victoria Derbyshire programme found.
Many, including two contestants on Love Island, took their own lives between April 2018 and March 2019.
Coroners have reported seeing a rise in such cases.
The charity Inquest uses the term "self-inflicted" to describe deaths where a person had injured or harmed themselves, resulting in death.
The programme has also uncovered a death in similar circumstances in Wales during the same period, and there were also another five in England where cocaine and alcohol were consumed but coroners said there was not enough evidence to record suicide conclusions.
One of those was Logan Woolliscroft, 21, who died after falling off a cliff near the family's Derbyshire home in 2018.
His father, Steve, said he found 8g of cocaine bags and a bottle of Disaronno liqueur at the top of the cliff and "just knew" he had fallen. Police then found his body.
Logan had become increasingly volatile and depressed in the three months before his death, Steve said.
He had made some new friends and started taking cocaine and drinking heavily.
The coroner said while Logan left notes for his family, he could have fallen while intoxicated and recorded an open conclusion.
Steve says he believes "100%" that taking cocaine and alcohol together caused his death.
"To mix a stimulant with a depressant, it muddles your brain up completely and you just don't know where you are," he says.
Logan's sister, Tillie, added: "I like to think of who he was before. He was such a nice boy. To think of something like this changing someone in such a drastic way, it shows what it can do to you."
Figures show there has been a rise in the number of alcohol-and-cocaine-related deaths over the past two decades, plus an increase in cocaine use.
Professor of addiction psychiatry Julia Sinclair, who is chairwoman of the faculty of addictions at the Royal College of Psychiatrists, explained that alcohol and cocaine were very different pharmacologically.
"Alcohol is a depressant, it increases the levels of Gaba (gamma-aminobutyric acid) in the brain, which is like its handbrake and makes us feel less anxious.
"You add cocaine into the mix and you have a rocket-fuelled increased impulsivity which gives people the driver to complete an act that they may not otherwise do. It's like crossing a road in front of a car speeding towards you."
Some research in the US even suggests the mixture could increase the risk of suicide by a factor of 16.
There are calls for more research into the combination of alcohol and cocaine and its links with suicide or life-threatening behaviour.
Some doctors believe that when you mix the two the liver produces a substance called cocaethylene, which may temporarily enhance the high - but also increases blood pressure, poor judgement and violent thoughts.
Prof Sinclair said: "People are looking for what the ingredient that makes alcohol and cocaine such a toxic combo. It might be cocaethylene - but we don't know and everyone has a different response."