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The genome doubling agent colchicine was used effectively to obtain tetraploid plants in dragonhead. Treatment of apical meristem of seedlings was carried out in two stages. The first stage was when the cotyledon leaves emerged. The second stage was when the two true leaves emerged. Six levels of colchicine concentrations: 0, 0.05, 0.1, 0.2, 0.5, and 0.75% were applied in each of these stages. Seedling treatment in the stage of emergence of two true leaves with 0.1% colchicine solution proved to be the most effective in producing autotetraploids. Morphological, cytological and flow cytometry analyses showed the increase of chromosome numbers from 2n= 2x= 10 to 2n= 4x= 20. The increase of ploidy levels caused major changes in some morphological and physiological traits and active substances in dragonhead.