Long-term laughing gas abuse contributed to a 24-year-old student’s death, an inquest has ruled. Ellen Mercer inhaled up to three “big bottles” of nitrous oxide every day, Berkshire coroner’s court heard. Mercer was taken to Wexham Park hospital for emergency treatment in the early hours of 9 February last year after she reported that she could not walk and would fall over when she tried. Medical staff treated Mercer, but she was found unresponsive the next day and was pronounced dead on 10 February. At the time of the student’s death, getting high on the substance was not illegal. The government made laughing gas a class C drug last November, and possessing it for its psychoactive effects can carry a custodial sentence of up to two years. In the last year, 1.3% of people aged 16 to 59 years and 4.2% of those aged 16 to 24 used nitrous oxide. This was a 48% and 54% decrease compared with the year ending March 2020. The inquest heard that Mercer, from Gerrards Cross, Buckinghamshire, was unable to leave her bed for a fortnight before her death due to abusing the substance. A postmortem examination found the cause of death was bilateral pulmonary thromboembolism, deep vein thrombosis and “long-term complications of nitrous oxide use”. Concluding the inquest, the senior coroner, Heidi Connor, said Mercer’s immobility had contributed to her death. “Ellen Mercer’s death was caused by nitrous oxide abuse and immobility that led to the development of a pulmonary embolism,” she said. Connor said: “This case has highlighted how hugely dangerous it is to use nitrous oxide. It is the nitrous oxide which has been the significant cause of her immobility.” According to the inquest, Mercer had been suffering from bipolar disorder but she was not receiving adequate support from local services, who failed to respond to her mental health review. On 8 February last year, Michaela Kirtley, an emergency medical technician from Phoenix Response Services, a contractor for South Central ambulance service, visited Mercer and was concerned about the state of her bedroom. “There were no sheets on the bed at all,” she said. “There was just the duvet, severely stained. The room was bare.” It was clear to Kirtley that she was dealing with a vulnerable person, but she said Mercer “was talking as normal”, and the only physical abnormality was a raised heart rate, which could have been caused by anxiety. Mercer’s boyfriend showed Kirtley a box of 600g canisters of gas. “I had never seen such big bottles,” she said. The inquest also heard that Mercer’s blood clot could have been identified earlier if hospital staff had performed a venous thromboembolism (VTE) assessment. However, the failure to do so did not cause her death.