Scientists looked at the dangers to both the individual and to wider society and found that alcohol was the most dangerous substance, according to the study by the Independent Scientific Committee on Drugs (ISCD).
The results fly in the face of long-held opinions about which drugs pose the greatest dangers, with the authors claiming they demonstrate "the present drug classification systems have little relation to the evidence of harm."
"They also accord with the conclusions of previous expert reports that aggressively targeting alcohol... is a valid and necessary public health strategy," said the authors.
Drug experts on the committee devised their own system to judge substances and believe their consensus provides a valuable assessment which could guide policymakers.
The research, published in medical journal The Lancet, looked at the how much a drug harms the human body as well as other factors such as what its use costs the health care and prison systems.
Heroin, crack cocaine and methamphetamine -- or crystal meth -- were found to be the most deadly. But when the wider social effects were factored in, alcohol was the most dangerous, followed by heroin and crack cocaine, said the study.
Substances were given a mark from zero to 100 based on certain criteria, with alcohol scoring 72 overall followed by 55 for heroin and 54 for crack.
One of the study's authors was David Nutt, a former British government drugs adviser during the previous Labour administration.
He was sacked after a disagreement with the government over the decision to upgrade the classification of cannabis.
The ISCD says its remit is to investigate and review scientific evidence relating to drugs, free from political concerns.
-MSN News
