The Advertising Standards Authority (ASA) has ordered 150 UK homeopaths to stop claiming they can care autism.
Five homeopaths are facing prosecution for advertising Cease "therapy", which is not supported by scientific evidence and can be harmful to children.
The National Autistic Society praised the advertising watchdog's decision, saying autism was not a disease to be cured but a lifelong part of many people's identity.
Cease, or Complete Elimination of Autistic Spectrum Expression, is supposedly a method of ridding children of toxins – including from vaccines and medication – that some homeopaths claim causes autism. Therapists claim they can care for children using homeopathic remedies and dietary supplements.
The treatment includes giving children time to five times more than is recommended by the Department of Health, and 200 times more vitamin C. Excessive quantities of vitamin C can cause diarrhea and vomiting. Cease therapists claim this is evidence of the child's body purging itself of toxins.
The ASA's chief executive, Guy Parker, told BBC Radio 4 there were concerns about false and potentially harmful treatments.
He said: “We felt enforcement to 150 Cease therapists operating in the UK. We have set up very clearly that they need to treat or treat their autism. Those failing to get their houses in order will be targeted with further sanctions. "
Experts say the therapy may be psychologically as well as physically damaging. Prof Nicola Martin, of London South Bank University, who advised the Westminster commission on autism, said: "It is really harmful to give parents the idea that the way to love and nurture their autistic child is to try and cure their autism."
The director of the National Autistic Society's Center for Autism, Carol Povey, said: "Many autistic people feel that their autism is a core part of their identity. It is deeply offensive to anyone to claim that they are unhealthy and therapies and products can 'cure' autism – and particularly appalling where people target vulnerable families. "
Said Emma Dalmayne: "As an autistic adult it disgusts me that these charlatans are taking advantage of parents."
A minority of Cease therapists in the UK are members of the Society of Homeopaths, which is regulated by the Professional Standards Authority. The society said the therapy may be renamed to avoid being misleading and it would take action to avoid further unfounded claims being made.
Cease was invented by a Dutch doctor, Tinus Smits, who died of cancer in 2010. Andrew Wakefield, a former gastroenterologist, was struck off the UK medical register in 2010 over his comprehensively discredited claim.