The availability of a test to detect cocaine in suspect powders that can be used 'on-the-spot' by Police is a welcome advance in controlling drug use. It will enable the Police to rule out whether a suspect substance is cocaine, although it will not test for other drugs. Previous on-the-spot tests used unpleasant chemical reactions to produce a coloured product and these reactions were prone to interferences. The new system uses antibodies to bind to cocaine in a test called an immunoassay, which is more specific and avoids the use of unpleasant chemicals.

However, even with immunoassay 'on-the-spot' tests, nothing is as simple as it seems. Previous experience has taught us that there may be interferences that cause a sample not containing cocaine to test positive or one that contains cocaine to test negative.

Positive results, which might be used to prosecute, need to be confirmed in a laboratory. This procedure is necessary because of the way these tests work - they 'recognise' the 3-dimensional structure of the drug molecule. Because of this, any other substance that 'looks' the same or similar as the drug can also give a positive test result. This other substance may be perfectly legal. Therefore over-reliance on the 'on-the-spot' test for Court proceedings would be foolish.

There can also be an interfering substance, which can 'mask' the drug in the on-the-spot test. If the Police strongly suspect that the suspect powder contains cocaine then they will send it to a laboratory for testing. The laboratory tests should be able to detect cocaine separately from the interfering substance.

So, this test will act as a deterrent and be of some assistance to the Police. Appropriate use of on-the-spot test results will be essential in any ensuing prosecution.