Health experts are urging people not to rely on untested remedies advertised on the Internet, insisting that they sell "false hope".
Backed by charity Sense About Science, the group of medical experts has revealed that the online promotion of treatments is increasingly exploiting vulnerable people.
According to them, many untested therapies being advertised on the Internet involve high costs, and do not work.
The experts say that such therapies are based on "unreliable" evidence.
Sense About Science says that people desperate for a cure are being targeted by hundreds of online advertisers.
The charity says that most online adverts and chat-room conversations testify to the "incredible" benefits of new medicines and treatments, often selling the empty promise of curing the incurable.
While some offer stem cell treatments for brain disorders for tens of thousands of pounds, others sell cures for multiple sclerosis and cancers.
However, the evidence backing the efficacy of such therapies is often unreliable, the experts say.
They insist that there should be tighter regulations to reduce unfounded claims.
"It can be tempting to believe personal stories of miracle cures, but only by using tried and tested methods can we move forward and provide people with Parkinson's with the best available advice and treatments," the BBC quoted Dr. Kieran Breen, director of research at the Parkinson's Disease Society, as saying.
Lib Dem MP Phil Willis, chairman of the Innovation, Universities, Science and Skills Select Committee, said that it would be the "cruellest deception" for a patient with chronic illness if he/she was promised a cure on the basis of "empty hope not evidence".
"This makes them particularly vulnerable to treatments that are supported only by anecdote and rumour," said Ian Douglas, who has multiple sclerosis.
Sense About Science, the Multiple Sclerosis Society, Motor Neurone Disease Association, Alzheimer's Society, and Parkinson's Disease Society have now taken out a new guide to help patients recognise bogus treatments.
The new guidline is called I've got nothing to lose by trying it.
Hazel Thornton, a patient advocate who acts as a liaison between patients and healthcare providers, said that the guide would help people "bring a critical eye and a questioning mind to what they read and hear".