The call came at 6:15am. The voice on the line sounded artificial, almost computerised, with chattering background noise. It must be a sales call, thought Graham Bloor. He hung up.

It rang again. This time when Graham answered, he waited, listening — just in case. It was a hospital in Brighton. What he was told would change his life, and his family, forever.

His son Thomas, one of Graham’s 21-year-old triplets, was in intensive care. An overdose. The doctor said that Tom had gone into cardiac arrest and was “resuscitated in the community” — at the scene of the overdose, a party in Brighton — and that the family should come.

Graham, himself a doctor, knew the most important question to ask: What is Thomas’s score on the Glasgow Coma Scale? This tells you, following a trauma to the body, how grave the situation is, how deeply unconscious someone is. Anything less than 8 indicates severe brain injury.

“Three,” the doctor said.

Graham knew what this meant. His son’s brain was all but dead.

Ninety miles away in Eastbourne, another phone rang. Barbara Bloor picked up, irritated that her husband up in London would ring so early, just because he has to be awake at that time. But then she heard him say: “Thomas is in intensive care on a ventilator.”

“I remember screaming,” Barbara says now, four months on.

She began to pace up and down the landing of their family home where she and Graham had raised their boys, Thomas, Paddy, and Eoin. She had been a nurse for decades but now she did not know what to do. They had student lodgers staying. Things had to be organised. She ran to the car and started driving. Autopilot. Trying not to crash. Trying to get to the hospital.

Barbara and Graham both had the same thought: This means we’ll lose two sons. Their eldest triplet, Paddy — the cleverest, most extroverted of the three — had been fighting a drug problem for years. They had tried everything. They knew he might not survive. Now that Thomas was unlikely to make it, it was only a matter of time before they had only one son left.

But there was so much more that they were about to discover.

They would learn that the drug on which their son had overdosed was GHB. They had never heard of it. The potent intoxicant comes in either powder or liquid form, and suppresses the central nervous system into a high that users describe as a like a combination between alcohol and ecstasy: disinhibiting, euphorically.

While much of the media refers to it as a “date-rape” drug, within the LGBT community GHB is known as one of the three key drugs used in chemsex, the drug-fuelled sex scene particularly popular among gay men. Its rising use over the last decade has entwined with increasing availability: Dealers sell GHB through gay dating apps.

But the Bloors also did not know what makes this substance uniquely dangerous. They had no idea, either, how many people GHB kills. This is because no one knows what the total figures are. It takes months for the family to discover why there is such a blackout: why the data is so patchy and the response from the authorities is so scant. Silence surrounding such deaths, meanwhile, pervades.

The evidence that is available suggests in Britain alone it could be hundreds who die from GHB every year. A question, therefore, encircles these figures: How many people — how many gay men — have to die before something is done?

The Bloors want to challenge the stigma surrounding GHB and stop more young men dying. They invited BuzzFeed News to interview them and their other sons about what happened. It is the first time an entire family has spoken out about the loss of a loved one to GHB. Graham and Barbara Bloor are uncomfortable having their photo taken and disclosing the most personal details about their family, but, they say, they cannot allow this silence to continue.

“I feel we have to,” says Graham. If people do not start talking, he fears the drug will proliferate more widely. He knows, too, that there was only one reason his family uncovered the truth about their son’s death: chance.