Sussex University student Hester Stewart died after taking GBL
A ban on several drugs known as "legal highs" has come into force.
The substances, including GBL and BZP, become Class C drugs, with a possible two-year jail sentence for possession.
Ministers moved to classify them after a recommendation from the Advisory Council on the Misuse of Drugs and fears they are a threat to user health.
GBL was linked to the death of medical student Hester Stewart, 21, in Brighton last April. Her mother, Maryon, campaigned nationally for the ban.
So-called legal highs are typically man-made chemical substances designed to act like banned drugs.
"Joey" describes the effects of the cannabis-like substance, Spice
Scientists, officials and police officers have been concerned for several years that GBL, BZP and other so-called "legal highs" have been sold openly across Britain and on the internet, despite evidence that they can be harmful to health.
GBL, which metabolises in the body into the already banned drug GHB, will become a Class C drug carrying maximum jail terms of two years for possession and 14 years for supply.
Piperazines, of which BZP is the most popular, are also being made Class C drugs.
This group of drugs is popular on the club scene as an alternative to ecstasy and amphetamines.
Synthetic cannabis has also been banned and become a Class B drug. Possession of products such as "spice", a herbal mixture laced with psycho-active chemicals, now carries a maximum five-year jail term.
Fifteen anabolic steroids, associated with drug abuse in sport, have also been classified as Class C.
Police chiefs say their response will be proportionate and focused on dealers.
Home Secretary Alan Johnson said the government was committed to raising awareness of the dangers of psychoactive substances through its Frank campaign, but also wanted to send a clear message to those thinking of using the drugs.
"We are cracking down on so-called 'legal highs' which are an emerging threat, particularly to young people," said Mr Johnson.
"That is why we are making a range of these substances illegal from today with ground- breaking legislation which will also ban their related compounds."
Scientists at the Forensic Science Service laboratories have recently discovered that drug dealers in London have been using one of the newly-banned drugs to manufacture fake "crack cocaine".
The effects of GBL and BZP
Dean Ames of the FSS said: "We occasionally see materials that appear to be crack cocaine, that end up being innocuous substances [such as] candlewax as crack cocaine.
"But, quite recently, we have seen a new form of drug that has been submitted to us that actually contains piperazines and would resemble a crack cocaine-type substance."
Piperazines were first developed as a worming agent and are also used in some manufacturing processes. The FSS says "legal highs" based on the chemical have become more prevalent than ecstasy.
Wednesday's ban is unlikely to be the last. The Advisory Council on the Misuse of Drugs will next year consider a new wave of so-called "legal highs", which are based on a group of chemicals known as cathinones.
However, the recent controversy over the sacking of the council's chairman, Professor David Nutt, and the subsequent resignation of council members in protest, could mean any final recommendations are delayed.
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