Britain's leading scientific institutions say changes to the regulation of homeopathic medicines are putting patients at risk.
Homeopathy has long been controversial
In addition, hundreds of doctors and scientists have signed a statement opposing the rules allowing homeopathic medicines to make medical claims.
The comments have been released as the House of Lords debates the new regulations.
But the drug regulatory agency said the new rules would benefit patients.
In September, the Medicines and Healthcare products Regulatory Agency (MHRA) introduced rules to allow homeopathic remedies to specify the ailments for which they can be used.
In a statement, the Royal College of Pathologists said they were "deeply alarmed" that the regulation of medicine had "moved away from science and clear information for the public".
The Medical Research Council said claims should not be made about efficacy of products without "rigorous and objective evidence".
And the BioSciences Federation warned the MHRA's decision was of "extreme concern" adding "it seems in this case that the MHRA has bowed to industry pressure".
In total, 12 national societies have raised fears over patient safety and accuracy of information, including the Physiological Society, the British Pharmacological Society, the Society for Applied Microbiology, the Royal Society and the Academy of Medical Sciences.
Sense about Science, which has been collating opinion on the issue, says 600 doctors and scientists have also signed a statement which says homeopathic medicines should not be allowed to make "unsubstantiated health claims" and that the policy is "damaging to patients' best interests".
Homeopathy is a system of therapy based on the concept that disease can be treated with drugs (in minute doses) thought capable of producing the same symptoms in healthy people as the disease itself.
Under the voluntary scheme, called the National Rules Scheme, homeopathic products will receive a licence if they can provide data proving the treatments are safe.
But they will not have to produce evidence of efficacy from clinical trials, unlike conventional medicines.
They will also be allowed to indicate what sort of symptoms they can relieve, although this will be limited to minor ailments such as colds, coughs and hay fever.
To make such a claim, the manufacturers need only show that the product has been used to treat those particular conditions within the homeopathic industry.
Critics have also been angered by suggestions that the MHRA has been partly motivated by a desire to boost the homeopathic industry.
In its consultation, the MHRA said failure to introduce the new system would inhibit the industry's expansion.
Lord Dick Taverne, chair of Sense About Science, who is taking part in the House of Lords debate on the regulation change said: "As many of the medical specialists contacting us have pointed out, evidence-based medicine has been a major public gain of the 20th Century.
"This is the first time, since the thalidomide tragedy and the 1968 Medicines Act, that the regulation of medicines has moved away from the science rather than towards it."
'Storm in a teacup'
But Dr Peter Fisher, clinical director of the Royal London Homeopathic Hospital said: "The regulations just tidy up the situation by saying 'this homeopathic medicine has been traditionally used for' and it brings it into line with the regulations for herbal medicines.
"I think it's a bit of a storm in a teacup," he added.
A spokesperson for the MHRA said: "The National Rules Scheme provides a significant opportunity to improve consumer information about the use of homeopathic products on the UK market whilst maintaining rigorous control over their quality and safety.
"The scheme requires that products have patient information leaflets which are regulated to the same standards as conventional medicines, ensuring that they are clear and comprehensive."