Desogestrel (abbreviated DSGS), is a progestin medication which is used as contraceptive agent, but also in the treatment of menopausal symptoms in women, used alone or along to an estrogen (usually ethinylestradiol), in solid dosage forms [1,2]. DSGS is formulated as tablets with a content of 100 to 125 μg in combination with ethinylestradiol, while solid formulations on Romanian pharmaceutical market containinig soleily DSGS are at a strength of 75 μg per tablet [3,4]. Structural formula of DSGS is presented in Fig.1. Since solid formulations contain low quantities of DSGS (order of micrograms), it is important to seek the possible interactions occurring between the active pharmaceutical ingredient and excipients, that at these low concentrations can drastically affect biodisponibility. Fig.1. Structural formula of DSGS Following these considerations, the compatibility between DSGS and some pharmaceutical excipients (sodium carboxymethyl-cellulose, tylose, methocel, talc, magnesium citrate, mannitol, starch, calcium lactate, magnesium stearate, colloidal silica and polyvinylpyrrolidone) was studied. All samples were initially investigated by ATR-FTIR spectroscopy under ambient conditions (20-25 °C), followed by subjection to thermal stress, in open crucibles (TG/DTG/HF), in oxidative atmosphere. A discussion regarding the compatibility between DSGS and each excipient is presented