The worst-rated drugs were alcohol, tobacco, nicotine and cocaine.

Prescribed drugs, such as antidepressants, were generally not well rated for treating eating-disorder symptoms but were positively rated for effects on general mental health.

The research, led by PhD student Sarah-Catherine Rodan at the University of Sydney's Lambert Initiative for Cannabinoid Therapeutics, is published on July 22 in JAMA Network Open.

Ms Rodan said: "Our results provide important insights into the lived experiences of people with eating disorders and their drug use, highlighting promising avenues for future research into treatments.

"The findings suggest more research, including large clinical trials, should be undertaken around the beneficial effects of cannabis and psychedelics for people with eating disorders."

The Lambert Initiative researchers will shortly launch a clinical trial of psilocybin in treating anorexia nervosa in collaboration with the Inside Out Institute at the University of Sydney.

Scope and response of survey

The study analyzed responses from over 7600 self-allocated participants in 83 countries, making it the most comprehensive survey ever conducted on this topic.

The research focused on how people with different types of eating disorders use prescription and non-prescription drugs, and how they perceive these substances' effects on their mental health and eating disorder symptoms.

The major categories of eating disorders were well-represented in the survey: anorexia nervosa (40%); bulimia nervosa (19%); binge-eating disorder (11%); and avoidant/restrictive food intake disorder (ARFID) (9%). About one third of respondents were not formally diagnosed with an eating disorder but self-reported an eating disorder that caused distress.

Co-morbid mental health conditions, which are often found in these populations, were frequently reported including depression (65%), generalised anxiety disorder (55%), ADHD (33%), drug dependence (15%) and alcohol dependence (9%).

Respondents were predominantly female (94%), with most from English-speaking places, like Australia (30%), the UK (21.3%) and the US (18%).

The results revealed patients with eating disorders have high rates of cannabis and psychedelic use relative to the general populations and rate their effects positively in terms of managing symptoms. Notably, cannabis was highly rated by respondents with restrictive eating disorders such as anorexia and ARFID, most likely because it enhances the rewarding value of food, addressing a core issue in these eating disorders.

In contrast, prescription stimulants such as lisdexamfetamine, which have strong appetite suppressing effects and are sometimes prescribed for binge eating disorder (BED), were positively rated by people with BED but poorly rated by those with restrictive type disorders.

Psychedelics, typically only taken once or twice a year by respondents, were reported to have remarkable long-lasting benefits, supporting recent research showing their therapeutic potential in treating conditions such as depression and anxiety. Conversely, commonly prescribed medications - such as antidepressants - which are typically taken daily, were generally rated as relatively ineffective for reducing ED symptoms but were widely acknowledged to help with overall mental health.

The survey also found that drugs like alcohol, nicotine, and cocaine, although quite widely used, led to negative outcomes on eating disorder symptoms and general mental health.

Ms Rodan said: "These findings highlight an important pattern: with traditional medications often falling short in treating eating disorders directly, while many individuals are self-medicating with substances they perceive as helpful. This underlines the urgent need to better investigate these substances in rigorously controlled clinical trials."

Next steps: clinical trials

The insights gained by this study have already prompted further research initiatives. The Lambert Initiative, in collaboration with the Inside Out Institute at the University of Sydney, is preparing to launch a clinical trial of psilocybin in treating anorexia nervosa. Additionally, a pilot study examining the therapeutic potential of the non-intoxicating cannabis component, cannabidiol (CBD), in treating severe anorexia in young people, is nearing completion.

Professor Iain McGregor, the senior author on this paper and Academic Director of the Lambert Initiative, said: "This research suggests that cannabis and psychedelics hold significant promise for improving quality of life in individuals suffering eating disorders. This is particularly salient since current pharmacological options for these patients are severely limited and current treatment outcomes so disappointing.

"Of course, rigorous clinical trials are needed to confirm these benefits and better determine safety profiles."

Ms Rodan said: "I hope this study gives a voice to people living with eating disorders, revealing that their often-stigmatized experiences with drugs might in fact have therapeutic potential. We are extremely grateful to the many thousands of respondents who took the time to provide such detailed responses around their lived experiences. This should spur further research and open new treatment pathways for these challenging conditions."

The study was funded by the Lambert Initiative for Cannabinoid Therapeutics, a philanthropically funded research program at the University of Sydney. Researchers report funding support from the National Health and Medical Research Council of Australia. Dr Anastasia Suraev reports consulting fees from the Medicinal Cannabis Industry Australia (MCIA). Professor Iain McGregor receives fees from Althea, Jannssen and the MCIA. He also has share options with Kinoxis Therapeutics, consultancies with Psylo and Emyria and patents with Kinoxis.