The home secretary's plans to clamp down on some currently legal drugs are lacking in clarity, experts have warned.
Alan Johnson announced on Tuesday that a range of drugs and a man-made cannabis substitute are to be banned by the end of the year.
At present, the government said, these "legal highs" are available to purchase and are an "emerging threat".
The two drugs, known as BZP and GBL, have been linked to a number of deaths.
Both will become Class C drugs and banned when intended for human consumption, meaning users could be punished with a two-year jail term while dealers would face sentences of up to 14 years.
The Home Office said it will launch an awareness campaign when students begin university in September.
Johnson said: "There is a perception that many of the so called 'legal highs' are harmless, however in some cases people can be ingesting dangerous industrial fluids or smoking chemicals that can be even more harmful than cannabis.
"Legal highs are an emerging threat, particularly to young people, and we have a duty to educate them about the dangers.
"That's why we are also launching a campaign in September to highlight the risks."
Martin Barnes, chief executive of the charity DrugScope, supported the government's decision to ban the drugs but warned that the law alone was a "blunt instrument".
"We have concerns that in lumping all these substances together as 'legal highs', the significant differences in the effects and potential harms might be hard for young people to identify," he added.
"It is important that public information and education campaigns are comprehensive and ongoing."
The announcement came as shadow home secretary Chris Grayling attacked the government's record on tackling drugs, saying some cities in Britain have the same culture of gangs and violence as seen in parts of the United States.
Dods Parliamentary Communications Ltd