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Thymus vulgaris L. is widely used as an ingredient in cooking and in herbal medicine. However, there is little information about its toxicity. The present study was performed to evaluate the acute and repeated 28-day oral dose toxicity of thyme essential oil in rats. For the acute toxicity test, two groups of three rats were used. The rats received a single dose of essential oil: 300 or 2,000 mg/kg of body weight (bw). The rats were observed individually during the first four hours, and then daily until day 14. For the toxicity test with repeated doses, four groups of 10 rats were used. Doses of 100, 250, and 500 mg/kg/day were tested for 28 days. At the end of the experiment, blood was collected and the animals were sacrificed. Histopathological examination showed that in the lungs of rats given the 2,000 mg/kg bw dose, polymorph nuclear infiltrates, hemosiderin macrophages, and interstitial space thickening were present. In the repeated dose study, all rats survived the 28-day treatment period and apparently showed no signs of toxicity. The hematological and biochemical parameters were not altered. The histopathological study of the organs showed severe changes in the lung, with the dose of 500 mg/kg/day; in the other organs, no alterations were observed or the changes were slight. The body weight was only altered in male rats given the 500 mg/kg dose. The relative weight of the organs did not show any significant changes. Our studies revealed that the essential oil of Thymus vulgaris has moderate oral toxicity according to the results of the acute test, whereas the results of the 28-day oral toxicity test suggest that the no-observed-adverse effect level (NOAEL) is greater than 250 mg/kg/day.

C. citratus essential oil and carvacrol have shown an antitumor effect on breast tumor cell lines, the main objective of this research was to evaluate the antitumor effect of the essential oil of Cymbopogon citratus (EOCc) and carvacrol on 7,12-dimethylbenz [a] anthracene (DMBA)-induced breast cancer in female rats. Cancer was induced by a single administration of DMBA at dose of 80 mg/kg body weight (BW). A total of 54 female Holtzman rats were randomly assigned into 9 groups (n = 6). Group I: PS (Physiological saline), Group II: DMBA, Groups III, IV, and V: DMBA + EOCc at doses of 50, 100 and 200 mg/kg/day BW, respectively, Groups VI, VII, and VIII: DMBA + carvacrol at doses of 50, 100 and 200 mg/kg/day BW, respectively, and group IX: DMBA + EOCc + carvacrol at doses of 100 mg/kg/day BW. The treatment lasted 14 weeks. As results, EOCc showed a reduction in tumors as well as necrosis and mitosis. Animals treated with carvacrol did not show necrosis, mitosis, or infiltration. Carvacrol at dose of 100 mg/kg/day BW revealed a significant decrease in the cumulative tumor volume down to 0.11 &plusmn, 0.05 cm3 compared to 0.38 &plusmn, 0.04 cm3 of the DMBA group (p &lt, 0.01). It is concluded that EOCc and carvacrol had an antitumor effect on DMBA-induced breast cancer in female rats.