This is the advice of Dr Carine Smith, a researcher in, among other things, the effects of indigenous plants at the Department of Physiological Sciences at Stellenbosch University (SU). Dr Smith recently published research on the effect of kougoed in vivo on the psychological stress of rats in the Journal of Ethnopharmacology.
Her research shows, among other things, that too big an intake of kougoed can lead to diarrhoea and suppression of certain parts of the immune system.
Sceletium tortuosum - traditionally also known as kougoed (literally, 'something to chew') or kanna - is a succulent-like ground cover that grows particularly in western and eastern South Africa, favouring quartzite soil. The Khoi, we are told, chewed or smoked kougoed or fermented it before use as a sedative with anxiety-alleviating properties and as a light anaesthetic for toothache.
"It's also traditionally used for constipation," Dr Smith adds. This effect may be due to the mesembrine alkaloid in the plant's leaves.
"So much of the information and so many claims about the benefits of kougoed that one finds on the internet and in books have never been tested scientifically with the appropriate controls - they're based simply on untested tales and anecdotes," she says.
"As in the case of any product with so-called healing properties, it's important to prove scientifically that people really benefit from it and that it's not just the placebo effect at play."
Dr Smith's studies show that dried kougoed has a limited positive effect on anxiety when taken in a low daily dose of approximately 5mg/kg body mass.
What concerns her, however, are the numerous negative effects that she has observed. When rats were given an increased dose of kougoed - 20 mg - they showed signs of, among other things, inflammation, diarrhoea and other forms of irritation of the alimentary canal. The immune system may also be suppressed by increased ingestion.
Dr Smith, who has already done considerable work on various indigenous plants, says that kougoed showed significantly more negative effects than did other natural substances, such as Sutherlandia, which she had tested before in the same way.
"It's absolutely essential that more research be done to determine the optimal therapeutic dose for kougoed and other indigenous products," she maintains. "There's a fine line between what's therapeutically good and what is, in fact, detrimental."
Dr Smith believes that too few scientific tests are generally done to determine suitable doses for natural herbal products.
"It can also be dangerous to use a product just preventively without your having a specific condition - in that case, the product could have a non-desirable effect," she warns. It is important to find out as much as possible about all the effects of a substance and of the effects of product preparation before starting to take it indiscriminately over a long period.
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