Blood, urine, and hair are the most frequent sample types utilised by forensic toxicologists because they are simple to collect non-invasively and offer a wealth of information on the past and current effects of different chemicals. Examining the gastrointestinal tract's contents as part of the collection of post-mortem samples is common and is likely to turn up traces of medications or poisons that have been taken but have not yet been fully digested. Additionally, the brain, spleen, vitreous of the eye, liver, and spleen may include important information on the cause of death. Blood samples can be used to determine if they were using any drugs or other pollutants at the time the sample was taken. Blood is one of the most crucial forensic toxicology samples, and it is advised to get samples from the heart and an extremity in post-mortem situations since trauma or the diffusion of drugs through tissue might taint the sample. Each compound's retention time can be utilised to deduce the structure of that component. Even when a drug is present at extremely low concentrations, gas-liquid chromatography, mass spectrometry, and Nuclear Magnetic Resonance (NMR) spectroscopy offer enough information to identify and quantify the component. Before using more in-depth analytical techniques, a variety of preliminary screening tests are often carried out to provisionally check for the existence of specific substances. These tests, which are frequently colorimetric in nature, might either signal that more testing is necessary or not.