The flares of active galactic nuclei (AGNs) can be used to detect or constrain Lorentz invariance violation (LIV) by measuring time lags in detection of high energetic photons. An important source of uncertainty is our lack of knowledge of source intrinsic processes. However, combining flares and sources allows us to increase the precision of these measurements as well as to limit the noise of intrinsic source effects. Cherenkov Telescope Array (CTA) will be the next generation of TeV gamma-ray observatory. I will present the first results obtained searching for LIV from the data recorded by its first prototype, the Large Sized Telescope (LST-1).
