A deuterated drug is a small molecule in which one or more of the hydrogen atoms are replaced by deuterium.

As deuterium and hydrogen have nearly the same physical properties, deuterium substitution is the smallest structural change that can be made to a molecule

Deuterium-carbon”bonds are 6 to 10 times more stable than the corresponding carbon-hydrogen bonds

• More difficult to break

• Slows the rate of bond cleavage: Kinetic Deuterium Isotope effect (KDIE)

• KDIE can impact the biological fate of many drugs that are metabolised by pathways involving carbon-hydrogen bond scission