Isotope Labelled Compound is a chemical substance in which part of the molecules are labeled with an isotope so that observations the isotopic composition make it possible to follow the compound or its fragments through physical, chemical, or biological processes. Isotopic labeling of compounds is a non-radioactive method of labeling, provides site-specific investigation of structures, makes molecules easily detectable by mass spectrometry and NMR, maintaining the physico-chemical properties of the target molecule, and is cost-effective and easy to use.

For Example Deuterium is a non-radioactive isotope of hydrogen that is a different atom than hydrogen. High Pure and well characterized Deuterated Compounds and Isotope Labelled Compounds are used as Internal Standards in Bio-Analytical BA/BE Studies.

• Isotope Labelled Compound is a chemical substance in which part of the molecules are labelled with an isotope so that observations the isotopic composition make it possible to follow the compound or its fragments through physical, chemical, or biological processes. Isotopic labelling of compounds is a non-radioactive method of labelling , provides site-specific investigation of structures, makes molecules easily detectable by mass spectrometry and NMR, maintaining the physico-chemical properties of the target molecule, and is cost-effective and easy to use. 
• For Example Deuterium is a non-radioactive isotope of hydrogen that is a different atom than hydrogen. High Pure and well characterized Deuterated Compounds and Isotope Labelled Compounds are used as Internal Pharmaceutical Standards in Bio-Analytical BA/BE Studies. 

• Stable isotopes can be incorporated into a molecule, producing a molecule with a higher molecular weight than that of the unlabelled molecule.
• Stable isotopically labelled compounds are non-radioactive chemical substances where one or more element within a compound has been substituted for its stable isotope. Common stable isotopes used in research include 2 H (Deuterium or D), 13C, 15N and 18O. 
• Stable as well as radioactive isotopes of carbon and hydrogen are natural constituents of living organisms. The stable isotopes, 2H and 13C occur naturally at abundances of 0.015 and 1.1%, respectively. 
• Stable isotope-labelled compounds have been synthesized and utilized by scientists from various areas of biomedical research during the last several decades. Compounds labelled with stable isotopes, such as deuterium and carbon-13, have been used effectively by drug metabolism scientists and toxicologists to gain better understanding of drugs’ disposition and their potential role in target organ toxicities . 
• Stable isotopes are non-radioactive chemical tracers that are largely underutilized in the pharmaceutical industry. Stable isotope ratios are measured by combustion and mass spectrometric analyses of bulk phases or specific compounds. Bulk phases typically are analysed by off-line combustion followed by dual-inlet mass spectrometry (MS) or by on-line combustion coupled with isotope-ratio-monitoring MS (irmMS). Specific compounds are analysed by either gas or liquid chromatography and irmMS, depending on the chromatographic properties of the analytes 
• Stable isotopes labelled compounds are in natural environments have been identified for 81 elements, from hydrogen to lead. Contrasting with radioactive isotopes, which are mostly used for dating or deciphering mixing processes, stable isotopes can be applied to trace any type of physicochemical reaction such as diffusion, dissolution/precipitation, oxidation/reduction, acid/base exchange, evaporation/condensation, or adsorption. Stable isotopes can be useful to distinguish biotic from abiotic signatures recorded in ancient terrestrial rocks or meteorites. 
• Stable isotopes are non-radioactive forms of atoms. Although they do not emit radiation, their unique properties enable them to be used in a broad variety of applications, including water and soil management, environmental studies, nutrition assessment studies and forensics. . 
• Stable isotopes can also be used as tracers, which are deliberately added to a system that is to be studied, such as in agriculture or nutrition. For this purpose, they must be separated using highly sophisticated techniques, such as mass spectrometry . 
• Stable isotopes labelled compounds can be used by measuring their amounts and proportions in samples, for example in water samples. Naturally-occurring stable isotopes of water and other substances are used to trace the origin, history, sources, sinks and interactions in water, carbon and nitrogen cycles. 
• An important limit on the application of stable isotopes as tracers of life is that abiotic processes may mimic isotope fractionations usually ascribed to biogenic origin. For instance, several experimental studies demonstrated that the production of organic carbon through abiotic pathways such as Fischer-Tropsch reactions generates C isotope compositions similar to those expected for biological pathways. 
• Stable isotope labelled compounds improved metabolic profile may potentially reduce or eliminate unwanted side effects or undesirable drug interactions.
• Stable isotopes labelled compounds are improved oral bioavailability , Deuteration in some compounds has reduced the presystemic metabolism that occurs in the digestive track allowing more of the unmetabolized drug to reach its target 
• Stable isotopes labelled compounds are increased half-life, stable isotope labelled compounds can have a slower pharmacokinetic affect extending the absorption and distribution in the body. This may decrease the number of doses that a patient may require in certain time period compared to its non-deuterated counterpart.