Anandamide-d4 is primarily used as an internal standard in mass spectrometry-based analytical methods. Its main application lies in the accurate quantification of anandamide, an endogenous cannabinoid neurotransmitter, in biological samples such as plasma, serum, brain tissue, and cerebrospinal fluid. Due to its deuterated structure, it closely mimics the behavior of native anandamide during sample extraction and chromatographic separation while being distinguishable by mass detection. This allows researchers to correct for variability in sample preparation, instrument response, and matrix effects. It is widely employed in pharmacokinetic studies, neuroscience research, and clinical diagnostics involving the endocannabinoid system. The ethanol solution format ensures ready solubility and ease of handling in laboratory workflows.