Healthy volunteers who participated in an experiment were asked to complete a questionnaire about their experiences. Special attention was paid to their motives and the informed consent procedure. The motives of healthy volunteers for participating in a study differed according to age. Young volunteers mostly participated because of the financial compensation, while older volunteers mainly participated to get a medical check-up, which was part of the selection procedure, or because of the benefit that other people might obtain from the results of the experiment. In most experiments the volunteers were content with the information given about the experiment, which was provided orally and in a hand-out. The information procedure was crucial for the experiment, because optimum information was of the utmost importance in keeping the volunteers motivated during the experiment. Another conclusion was that the researcher should not be afraid that too much information was given. Adequate information was also important in recruiting new volunteers, because they mostly become interested because of information obtained from their predecessors. A personal approach towards the volunteers during the experiment was appreciated by them and was an important help in keeping the volunteers motivated during the experiment.

Because from earlier experiments in rats and a pilot study in humans a no effect level of glycyrrhizic acid could not be established, a second experiment was performed in healthy volunteers. The experiment was performed in females only, because the effects were most marked in females in the pilot study. Doses of 0, 1, 2 and 4 mg glycyrrhizic acid/kg body weight were administered orally for 8 weeks to 39 healthy female volunteers aged 19-40 years. The experimentlasted 12 weeks including an adaptation and a “wash-out” period.Ano-effectlevel of2 mg/kgis proposed from the results ofthis study, from which an acceptable daily intake (ADI) of 0.2 mg/kg body weight can be extrapolated with a safety factor of 10. This means consumption of 12 mg glycyrrhizic acid/day for a person with a body weight of 60 kg. This would be equal to 6 g licorice a day, assuming that licorice contains 0.2% of glycyrrhizic acid. The proposed ADI is below the limit advised by the Dutch Nutrition Council of 200 mg glycyrrhizic acid/day. This reflects the relatively mild acute toxicity of glycyrrhizic acid, which is also emphasised by the “generally recognised as safe” (GRAS) status of glycyrrhizic acid in the USA in 1983. However, the long-term effects of a mild chronic intoxication (causing, for example, a mild hypertension), although not immediately lethal, justify special attention to the amount of glycyrrhizic acid used daily.

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