Sold as heroin, it actually contains alprazolam which when injected or inhaled can cause hypoventilation (respiratory depression), slow down the heart and potentially cause death, especially when mixed with alcohol.

Reports have come in from Dorchester, Bournemouth, Wareham, Guildford, Woking, Camberly, and Hastings in East Sussex, where four cases of respiratory arrest linked to overdoses were reported yesterday afternoon. The substance is believed to have originated in the Thames Valley area.

The substance is brown with a red/orange tint. When burnt it appears to go orange, when chased it goes liquid orange and seems sticky, even after a day on the foil. When cooked to inject it is reported that it turns different colours such as black, dark green, dark red (probably other cuts).

Symptoms include extreme drowsiness, lethargy, flu-like symptoms, shaking, vomiting and forgetfulness. It should be noted that these symptoms are similar to withdrawal symptoms, as the so-called heroin may contain no opiates and block the effect of other opiates taken.

If symptoms occur the user must be taken to hospital where treatments are available including flumazenil or another benzodiazepine antagonist.

Another substitute increasingly being found is Subutex. Using Subutex on top of heroin can precipitate symptoms of full withdrawal. Buprenorphine, the active ingredient of Subutex, is a partial opiate antagonist. This means that as well as preventing withdrawal and producing morphine-like effects, it can block the effects of heroin and thereby induce withdrawal symptoms, if used in conjunction with other opiates. It may prevent opiates taken afterwards from being effective. To find out more information on Subutex click here for more information on the Release website.

Whilst the substitute alprazolam has been found in the South of England, its presence has been linked to a UK-wide shortage of heroin. This shortage has even caused an estimated 20% rise in the price of methodone, despite prices having remained constant for more than 20 years. Other factors thought to have contributed to this rise include 'supervised consumption,' the inconvenience of daily-pickups, and a more target-based approach to treatment, leading drug users to seek methodone outside of treatment centres during a drought such as this.

Shortages are not uncommon but usually correct themselves. However the drug is still being heavily cut and producers are finding more ways of cutting corners, since the price of heroin bottomed out at around £35 a gram.

The increase in the number of dealers who are not themselves users means there is less reliable information about what users are actually buying, and users are advised to be vigilant.