Techniques for detecting narcotics such as tetrahydrocannabinol (THC) or other aerosols such as cannabinoids, opioids, etc., in an exhaled breath using infrared spectroscopy are provided. An example of an apparatus for sensing THC according to the disclosure includes a tunable laser source, at least one photodetector, a sample cell disposed between the tunable laser source and the at least one photodetector, and at least one processor operably coupled to the tunable laser source and the at least one photodetector and configured to provide a control signal to the tunable laser source, determine a spectral absorption line or group of absorption lines associated with THC based on an intensity of infrared light detected by the at least one photodetector, and determine a THC concentration value based on the spectral absorption line intensity. A laser-based apparatus for sensing narcotics in exhaled breath may include a single, dual, or multi-optical frequency comb spectrometer.