The Swiss regulatory authorities have warned against ordering high-dosage vitamins and mineral salts on the internet.
Officials said some of these imported products could lead to serious health problems for consumers.
Last year the Swiss Agency for Therapeutic Products, Swissmedic, checked about 1,600 imports of medication, mainly ordered online by private individuals.
Swissmedic said many of these imports were vitamins and mineral salts with an exceedingly high dosage.
The packages of medication bought online often gave inadequate information and did not mention possible negative side effects.
Some products were labelled as "herbal" and "natural" but contained chemical substances, Swissmedic said on Monday.
The agency also pointed out that an extremely high dosage of vitamin A, for example, could damage the liver and lead to serious psychological disorders.
The agency estimates that between 20,000 and 40,000 packages of medication bought online arrive in Switzerland every year.
Up to 8,000 of them contain banned narcotics or psychotropic drugs.
Medication ordered over the internet circumvented regular official checks, said Swissmedic.
In June the agency blocked a Swiss internet site which offered illegal medication from the United States. It also confiscated several kilograms of drugs.
In Switzerland, pharmacies need an official licence to operate, and deliver some drugs on prescription only.
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Swissmedic estimates that between 20,000 and 40,000 packages of medication are ordered over the internet in Switzerland every year.
Between 4,000 and 8,000 of these packages contain banned narcotics or psychotropic medication.