Abstract: The invention provides a method for preventing and fighting the harmful biological effects of free radicals in the organism of warm blooded animals and more especially human beings, namely cerebral involution, hypoxia following atherosclerosis, cardiac or cerebral infarction, tumour promotion, inflammation, ischaemia, alterations of the synovial liquid, collagen degradation, among others. The method consists in administering to said animals and especially to human beings an amount, efficient against said effects, of a plant extract with a proanthocyanidins content which has a radical scavenger effect, the extract being in the form of a medicament and coming more especially from the bark of conifers.