Drugs users across East Anglia were last night warned to exercise extreme caution after research showed cannabis supplies are being contaminated with harmful glass particles.

Drugs users across East Anglia were last night warned to exercise extreme caution after research showed cannabis supplies are being contaminated with harmful glass particles.

Campaign bodies lobbying for the legalisation of cannabis claim small glass beads - believed to be an industrial spray used for glass frosting - are being added to herbal cannabis in a bid to increase its weight and making “deals” more expensive.

Norwich-based group Cannaprag says police raids during the summer of 2006 which saw large scale cannabis farms - including several in Norwich, Yarmouth and King's Lynn - closed down have created a shortage of the drug meaning dealers are contaminating supplies in a bid to meet demand.

But this could have serious health consequences for thousands of users with some already reporting mouth ulcers, sore throats and chesty persistent coughs.

Cannaprag spokesman Derek Williams said the cannabis using community has had suspicions about contamination for about six months but has only now obtained evidence by analysing samples of the drug. At first the substance was thought to be a relatively harmless material such as sands but the results are far more worrying.

Mr Williams added: “What has become clear through this incident is that the government has no method of warning illegal drug users of dangers such as this and seemingly has no desire to do so.

“Government policy towards illegal drugs should not act in such a way as to increase the danger of using them by adding unknown risks.

“Cannaprag is calling for public information campaign to raise awareness of this contamination as a matter of urgency. It will be affecting a huge number of people. A public health warning is urgently needed to inform users that they should not smoke this contaminated cannabis and dealers should not sell it.”

Mr Williams said that such contamination is a result of prohibition and legalising cannabis would allow the government to ensure the safety of supplies.

“The reality is that people are going to use cannabis and, if that is the case, the government should have some way of ensuring their safety. The only way of doing this is through legalisation,” he said.

Magnification of three samples shows small beads 50 - 120 micrometers diameter, made of non-soluble high melting point glass like substance.

If smoked without a filter - as is common - these glass beads are drawn into the lungs.

The author of the research has remained anonymous but Cannaprag and other legalisation campaign groups are calling on the government to conduct its own research.