A deadly drug, which has been banned from the battlefield under the Chemical Weapons Convention and is being blamed for a spate of drug overdoses in the United States, can be easily bought over the internet for just a few thousand pounds, it has been revealed.

Twelve Chinese online businesses said they could export carfentanil – a synthetic opioid which is being cut with heroin and other illicit drugs - at just $2,750 (£2,233) to the US, Canada and various European countries including the UK, an investigation by the Associated Press found.

Carfentanil is the most potent commercial opioid in the world, according to the US Drug Enforcement Agency (DEA).

Its chemically similar cousin fentanyl is up to 50 times stronger the heroin and carfentanil is 100 times stronger than fentanyl itself.

Before being discovered by drug dealers, carfentanil and substances like it were viewed as chemical weapons. Assistant Secretary of Defence for Nuclear, Chemical and Biological Defence Programmes between 2009 and 2014 described the drug as a “weapon”, adding “companies shouldn't be just sending it to anybody”.

World's 10 deadliest street drugs Show all 10 1 /10 World's 10 deadliest street drugs World's 10 deadliest street drugs Whoonga Whoonga is a combination of antiretroviral drugs, used to treat HIV, and various cutting agents such as detergents and poisons. The drug is widely available in South Africa due to South Africa’s high rate of HIV sufferers, and is believed to be popular due to how cheap it is when compared to prescribed antiretrovirals. The drug is highly addictive and can cause major health issues such as internal bleeding, stomach ulcers and ultimately death Getty World's 10 deadliest street drugs Scopolamine Scopolamine is a derivative from the nightshade plant found in the Northern Indian region of South America (Ecuador, Colombia and Venezuela). It is generally found in a refined powder form, but can also be found as a tea. The drug is more often used by criminals due its high toxicity level (one gram is believed to be able to kill up to 20 people) making it a strong poison. However, it is also believed that the drug is blown into the faces of unexpecting victims, later causing them to lose all sense of self-control and becoming incapable of forming memories during the time they are under the influence of the drug. This tactic has reportedly been used by gangs in Colombia where there have been reports of people using scopolamine as way to convince victims to rob their own homes World's 10 deadliest street drugs Heroin Founded in 1874 by C. R. Alder Wright, heroin is one of the world’s oldest drugs. Originally it was prescribed as a strong painkiller used to treat chronic pain and physical trauma. However in 1971 it was made illegal under the Misuse of Drugs Act. Since then it has become one of the most destructive substances in the world, tearing apart communities and destroying families. The side effects of heroin include inflammation of the gums, cold sweats, a weak immune system, muscular weakness and insomnia. It can also damage blood vessels which can later cause gangrene if left untreated World's 10 deadliest street drugs Crack cocaine Crack cocaine first came about in the 1980’s when cocaine became a widespread commodity within the drug trafficking world. Originally cocaine would have attracted a high price tag due to its rarity and difficulty to produce, but once it became more widespread the price dropped significantly. This resulted in drug dealers forming their cocaine into rock like shapes by using baking soda as a way of distilling the powder down into rock form. People were doing this because it allowed for them to sell cocaine at a lower quantity and to a higher number of people. The side effects of crack cocaine include liver, kidney and lung damage, as well as permanent damage to blood vessels, which can often lead to heart attacks, strokes, and ultimately death World's 10 deadliest street drugs Crystal meth Not just famous because of a certain Walter H White, but also because it is one of the most destructive drugs in the world. First developed in 1887, it became widely used during the Second World War when both sides would give it to their troops to keep them awake. It is also believed that the Japanese gave it to their Kamikaze pilots before their suicide missions. After the war crystal meth was prescribed as a diet aid and remained legal until the 1970s. Since then it has fallen into the hands of Mexican gangs and has become a worldwide phenomenon, spreading throughout Europe and Asia. The effects of crystal meth are devastating. In the short-term users will become sleep depraved and anxious, and in the long-term it will cause their flesh to sink, as well as brain damage and damage of the blood vessels World's 10 deadliest street drugs AH-7921 AH-7921 is a synthetic opioid that was previously available to legally purchase online from vendors until it became a Class A in January 2015. The drug is believed to have 80% of the potency of morphine, and became known as the ‘legal heroin’. While there has only been one death related to AH-7921 in the UK, it is believed to be highly dangerous and capable of causing respiratory arrest and gangrene World's 10 deadliest street drugs Flakka Flakka is a stimulant with a similar chemical make-up to the amphetamine-like drug found in bath salts. While the drug was originally marketed as a legal high alternative to ecstasy, the effects are significantly different. The user will feel an elevated heart rate, enhanced emotions, and, if enough is digested, strong hallucinations. The drug can cause permanent psychological damage due to it affecting the mood regulating neurons that keep the mind’s serotonin and dopamine in check, as well as possibly causing heart failure World's 10 deadliest street drugs Bath salts Bath salts are a synthetic crystalline drug that is prevalent in the US. While they may sound harmless, they certainly aren’t the sort of salts you drop into a warm bath when having a relaxing night in, they are most similar to mephedrone, and have recently been featured throughout social media due to the ‘zombification’ of its. The name comes from the fact that the drug was originally sold online, and widely disguised as bath salts. The side effects include unusual psychiatric behaviour, psychosis, panic attacks and violent behaviour, as well as the possibility of a heart attack and an elevated body temperature World's 10 deadliest street drugs Purple Drank One of the more unusual drugs around at the moment, purple drank was popularised in 90s hip hop culture, with the likes of Jay Z and Big Moe all mentioning it in their songs. It is a concoction of soda water, sweets and cold medicine, and is drunk due to cold medicines high codeine content, which gives the user a woozy feeling. However it can also cause respiratory issues and heart failure World's 10 deadliest street drugs Krokodil Krokodil is Russia’s secret addiction. It is believed that over one million Russians are addicted to the drug. Users of krokodil are attracted to the drug due to its low price; it is sold at £20 a gram while heroin is sold for £60. However, krokodil is considered more dangerous than heroin because it is often homemade, with ingredients including painkillers, iodine, lighter fluid and industrial cleaning agents. This chemical make-up makes the drug highly dangerous and likely to cause gangrene, and eventually rotting of the flesh

The drug was first developed in the 1970s and its only official use is to sedate large zoo animals such as elephants. Just 10mg of carfentanil will sedate a 5000kg elephant.

A spate of overdoses in the US in recent months has been attributed to dealers lacing heroin and other substances with carfentanil to boost profit margins.

One of the worst-hit areas is Ohio where in Hamilton County there were more than 96 heroin overdoses and three deaths in under a week in late August, Fox 19 reports.

In nearby East Liverpool, the Ohio police department shared a photo of two adults who had overdosed in their car with a four-year-old child in the back.

In Ohio’s Cuyahoga County there were 14 opioid related overdoses in the first week of September, two of which were directly related to carfentanil, ABC 5 News reports.

"Our community has been devastated by heroin and fentanyl abuse,” said Hamilton County Coroner Dr Lakshmi K Sammarcoin in a statement released by Hamilton County Heroin Coalition. “The fact that there is a new lethal drug that has been found on the streets of Hamilton County is frightening.”

Heroin production on the rise in Mexico

In 2014, US authorities seized 3.7kg of fentanyl. This year, until mid-July, they have seized 134.1kg, according to US Customs and Border Protection data obtained by the AP. Fentanyl is the most frequently seized synthetic opioid, US Customs reports.

In China, however, carfentanil is not a controlled substance and it can be manufactured legally and sold openly online.

"We can supply carfentanil . for sure," a saleswoman from Jilin Tely Import and Export Co told the AP in an email in September. "And it's one of our hot sales product."

Vendors said they lie on customs forms, guaranteed delivery to countries where carfentanil is banned and volunteered strategic advice on sneaking packages past law enforcement.

At a chemicals industry conference in Shanghai last month, several vendors said they would be able to supply carfentanil and some also recommended sending the drugs via EMS, the express mail service of state-owned China Postal Express & Logistics Co.

China's Ministry of Public Security and EMS have not commented on the allegations.

Not all of the websites used to sell the drugs are based in China. At least six Chinese companies offering versions of fentanyl, including carfentanil, had IP addresses in the US, hosted at US commercial web providers, the AP found.

The US government has urged China to blacklist carfentanil, but Beijing has yet to act.

Most synthetic drugs that arrive in the US come from China, either directly or by way of Mexico, according to the DEA. China has already placed controls on 19 fentanyl-related compounds.