Smokers who rely on nicotine patches or chewing gum to help them kick the habit may continue to run an increased risk of heart disease.

Research by the Centre for Biological and Medical Systems of Imperial College, London, suggests that nicotine in any form alters blood circulation.

Ultrasound scans of the main thigh artery found significant short term changes in blood flow pattern and hardening of the artery wall soon after volunteers began to chew the gum.

The changes are similar to those brought on by smoking, say researchers.

In any event, many of the nicotine patches being used as aids to stop smoking have not been subjected to any regulatory scrutiny.

Only three products Nicabate, Nicorette, Nicotinell which can be bought from pharmacists have been scrutinized; the host of patches available through mail order have not.

"Their marketing, and the use of brandnames similar to those of the licensed products, seems to rely on the understandable difficulty that consumers will have in distinguishing genuine products from false," writes M J Jarvis et al from the ICRF Health Behaviour Unit at the National Addiction Centre (BMJ, 6 March 1993).