Neil McKeganey, director of the Centre for Drugs Misuse Research, said the fact that young people were willing to take increasing numbers of drugs without any knowledge of what is contained in them was a major concern.
It comes as investigations continue into the death of Regane MacColl at Glasgow's Arches nightclub after she is believed to have taken a drug named "mortal kombat".
Mr McKeganey said that in the past the number of drugs being taken recreationally was relatively small, with the effects and risks largely known to users.
He said the risks had intensified with the drug ecstasy but were now out of control due to the increasing number of substances being produced and sold including so-called 'legal highs' which are freely available on the high street.
He said: "We are facing a situation which is even more serious that it has been in the past.
"A culture has developed where there is a willingness to pop a pill without any knowledge of what it is and what chemical compounds are within the drugs.
The threat of how potentially damaging they are doesn't seem to be having any impact.
"In the past the number of drugs people were using was relatively small and it was pretty clear what these drugs were. We knew what the effects of LSD would be.
"Young people don't have the faintest idea what they are taking.
"It is difficult to dissuade young people from the view that the tablet is going to be about fun."
Mr McKeganey has urged the government to enforce tighter controls on shops that sell legal highs.
He said: "We should not have a situation that people can walk past a shop and believe a substance is safe because it's on sale in a shop.
"I think the Scottish Government has to take a much tighter control over retailers on the high street who are selling substances to young people that can have very serious health consequences."