Supplements containing the amino acid tryptophan are expected to be reintroduced onto the UK market in coming months, following a change in the law that has banned them for the last 15 years.
Lobbying by the health charity the Institute for Optimum Nutrition (ION) in 2002 prompted the UK's food authorities to re-examine the safety of tryptophan that had been thrown into doubt by health problems caused by a batch produced in Japan in 1989.
Based on the findings of a special committee on toxicity, the UK government will bring new laws into force next Friday that allow Laevorotatory tryptophan to be added to any food supplement as long as it meets certain criteria.
The criteria have however been disputed by both the ION and the supplement trade body HFMA as they limit doses of the amino acid to the "extremely conservative" level of 220mg, according to David Adams, executive director of the group.
He added that the law "compares unfavourably with that of other markets", such as the Netherlands that permits doses of up to 600mg, and Japan that allows 1g to be consumed in supplement form.
However further lobbying in parliament has resulted in a recent commitment by the health secretary Caroline Flint to review the dosage.
In a response to parliamentary questions on 28 October, she said: "We have asked COT to review its recommendation and any new information on tryptophan since June 2004, and this will be considered at the COT meeting in December. Depending on COT's advice the legislation may be amended."
She added however that in "the interests of consumer choice and safety", the food authorities have adopted the level and purity criteria originally proposed by COT, and this level will be adopted by the new law.
Adams said he still expected half a dozen companies to introduce low-dose products after 11 November. The supplement was once consumed by around 30 million consumers before being banned from the UK and US markets.
Known to regulate hormones and mood, there is good evidence of its benefit in people with insomnia and depression.
The law continues to prohibit the addition of tryptophan to food except for infant, follow-on, cereal-based or baby foods registered under PARNUTS (Products for Particular Nutritional Uses) legislation.