The war against synthetic drug heats up. On Wednesday, the US Drug Enforcement Administration (DEA) cracked down on designer drugs in a continuing execution of Project Synergy, which chalked up more than 150 arrests and a seizure of US$20 million (S$25 million) in cash and assets.

The first phase of the operation began in December 2012. In the sweep, more than 227 arrests across 35 states and five countries were made. A total of US$60 million in cash and assets and nearly 10,000kg of individually packaged drugs were also confiscated.

The message of the DEA's Project Synergy operation was clear. "Many who manufacture, distribute and sell these dangerous synthetic drugs found out first hand today that the DEA will target, find and prosecute those who have committed these crimes," said DEA administrator Michele Leonhart.

In New Zealand, Prime Minister John Key conceded that an attempt to regulate the synthetic-drugs market had failed. As a result, from May 8, 2014, the sale of all psychoactive products, such as synthetic cannabis, will be banned in the country.

The move mirrors Singapore's legislation, which lists New Psychoactive Substances as Class A controlled drugs as of May 1, 2014.

But what exactly is the furore over synthetic drugs about? How different are they from "natural" drugs? Which is more harmful?

Here's the lowdown on synthetic drugs:

Synthetic drugs are...
...drugs with properties and effects similar to a known hallucinogen or narcotic. Simply put, synthetic drugs are "those substances that are produced entirely from chemical reactions in a laboratory", according to the United Nations Office on Drugs and Crime, and they mimick illegal substances.

What's frightening about synthetic drugs is that no one really knows what goes into them. It is all in a day's work for manufacturers to constantly change the chemical compounds of the drugs just to dodge existing laws. What's more, they are highly addictive.

The problem of synthetic drugs, which also go by the monikers legal highs and designer drugs, has become so huge all over the world that the "bad guys" - meth, cocaine and heroin - now trail after them.

Most of the chemicals that are used to make these synthetic drugs are coming directly from China, according to DEA official John Scherbenske in a CNN interview late last year.

Time magazine reported in September 2013 that "suburban laboratories around Chinese port cities are the principle source, from where they can be easily shipped to Europe or North America using regular international courier services".

Synthetic drugs include...
...3,4-methylenedioxymethamphetamine or MDMA, which is more commonly known as Ecstasy and Molly. It is similar to stimulants amphetamine and mescaline, a hallucinogen, and comes in the form of tablets or capsules.

Why people take it: Ecstasy pills send users on an euphoric high for three to four hours, resulting in an emotionally relaxed and physically exhilarated state, according to Brown University's Health Education.
Negative effects: Confusion, depression, sleep problems, drug craving and anxiety. These may occur shortly after consumption, and even weeks after. Nausea, muscle tension, involuntary teeth clenching, blurred vision, faintness and chills can also occur.

...Lysergic acid diethylamide (LSD), also sometimes known as acid, Electric Kool-Aid, California Sunshine, dots and blotter. First hitting the streets in the early 1960s, the most widely-studied psychedelic soon became the drug of choice for hippies, with its mood-changing potency.

LSD is odourless, colourless and has a slightly bitter taste. Users lick it off a piece of paper.

An acid trip can last up to 12 hours.

Why people take it: The hallucinogenic, mind-altering drug's primary effects are visual. Colours and lights are sharpened, appearing stronger and brighter. There is an overall sense of happiness and everything is beautiful and magical.
Negative effects: Increased blood pressure, a high body temperature, dizziness, sweating, blurred vision, tingling in hands and feet, drowsiness (but not sleepiness), impulsiveness and poor judgement.

...Phencyclidine, or PCP, a recreational drug that was also used as a horse tranquiliser. Commonly known as Angel Dust, PCP is a white crystalline powder that readily dissolves in water or alcohol, and has a bitter chemical taste. This is when it is in its purest form.

But PCP sold on the streets can range from tan to brown and the consistency from powder to a gummy mass, depending on the level of contamination.

It is typically sprayed onto mint, parsley, oregano or marijuana leaves and smoked. It was a much more popular drug back in the 1970s than it is today.

Why people take it: PCP is dissociative in nature, and has sedative and out-of-body effects.
Negative effects: A decrease in blood pressure, pulse rate, and respiration. Possible nausea, vomiting, blurred vision, drooling, loss of balance and dizziness. High doses can result in illusions, hallucinations, seizures and coma.

...Spice, also called K2, which is also the world's most treacherous peak - perhaps there is good reason for the identical name. Spice is a potpourri of dried, shredded plant mixed with chemical additives to mimic the psychoactive ingredient in the marijuana plant.

The National Institute on Drug Abuse in the US cautioned that while Spice products do contain dried plant material, chemical analyses show that their active ingredients are synthetic cannabinoid compounds.

Spice is smoked or prepared as an herbal drink.

Just a few days ago, more than 30 people in Dallas overdosed on it in just one day, according USA Today.

Why people take it: Elevated mood, relaxation and altered perception, similar to what smoking marijuana induces. In some case, the effects are stronger.
Negative effects: Extreme anxiety, paranoia and hallucinations.

...bath salts, the newest kids on the synthetic drug block. They are crystallised chemicals that users snort, swallow or smoke. The two powerful stimulants in these drugs mimic cocaine, LSD and methamphetamine. They contain at least one synthetic chemical related to cathinone, an amphetamine-like stimulant found naturally in the Khat plant, according to the US National Institute on Drug Abuse.

They look like white or brown crystalline powder, and are sold under a variety of innocuous-sounding names - Ivory Wave, Bloom, Cloud Nine, Lunar Wave, Vanilla Sky and White Lightning - and the ominous Scarface. Packaged in small plastic or foil packages, they typically come with the label "not for human consumption". They are also marketed as jewellery cleaner, plant food or phone-screen cleaner.

Why people take it: Euphoria, increased sociability and a galvanised sex drive
Negative effects: Paranoia, agitation and hallucinatory delirium. Psychotic and violent behaviour is not uncommon. Deaths have also been reported.