The aim of the study was the analysis of the changes in the kind and the frequency of particular nutritional products consumption by opiate addicted persons during 4-year lasting methadone programme. There were 30 opiate addicted patients under examination (23 men and 7 women). Food consumption quality was estimated with the use of the Intake Frequency of Food Products Questionnaire. The examinations were performed before methadone administration had started, after 9 months and after 4 years of methadone maintenance treatment. Three categories of consumption frequency were established: rarely, moderately and often. The classification of different products was done with the use of hierarchic cluster analysis. For general illustration of the data the consumed products were compared by the means of hierarchical cluster analysis (this was done with the help of Euclidean distances and the Ward's algorithm). Then the k-means (with k=3) method was used in order to identify groups of products that were similarly often consumed. Each k-means analysis was performed separately for each examination. This was done in order to find out the products that change the cluster from one examination to another. Twenty labile products were identified. The examined products were moving between the adherent categories. This means that the consumption pattern undergoes some changes over the course of methadone therapy. Additionally, the analysis of the diet of this group of people shows improper and unhealthy nutritional behaviours: too big intake of sweets and too low intake of complex carbohydrates, fish and vegetable fats. This was especially visible at the beginning of the therapy, later this unfavourable diet habits changed but not to the desired level.