It's easy to understand why diet pills have such appeal to slimmers - for a few pounds you get a quick fix to your weight problem at no real effort.

The market for diet pills is huge - in the UK alone people spend ?9 million a year on slimming aids, much of it on diet pills.

Because many of these products are sold as herbal diet pills, there is a feeling that they will help you to lose weight 'naturally'. However, many doctors doubt both the safety and effectiveness of these herbal slimming aids.

Common ingredients include:

Alfalfa: This is often used in foods as a bulking agent to make you feel full and eat less. There is no research to suggest that it will help you lose weight.
Chitosan: This comes from the shells of crustaceans such as crabs and shrimps. It is claimed that it attracts and absorbs fat, but again, there is no evidence that it will help you lose weight. It should be avoided by anyone who is allergic to shellfish.
Hoodia gordonii: The big name in weight loss supplements, Hoodia is touted as a miracle extract that will reduce your appetite. While there are no proper clinical trials on hoodia, there is anecdotal evidence that it can suppress appetite.
Chromium Picolinate: Chromium does help to metabolize sugar, but you would only need to take this if you have a chromium deficiency, which is very rare.
Green tea extract: This is claimed to boost your metabolism and help you burn more fat. There is some evidence to support this claim, though the effect is small (3-5%).
Caffeine: often added to slimming supplements - it has a mild diuretic effect.
Fucus: A type of seaweed. Claimed to speed up metabolism, though no evidence supports this.