Lipophilicity is a physicochemical property that reflects how readily a molecule partitions into a non-polar, fatty environment relative to an aqueous one. It is conventionally expressed as the logarithm of the octanol–water partition coefficient, written as log P (or log D when the measurement accounts for ionisation state at a specific pH). A higher positive log P value indicates greater affinity for lipid environments; a negative value indicates stronger affinity for water.
The property is significant in pharmacology and biochemistry because it influences how a compound crosses biological membranes, including the blood–brain barrier and the intestinal epithelium. Compounds with moderate to high lipophilicity tend to diffuse more readily across phospholipid bilayers by passive transcellular transport. This has downstream consequences for absorption, distribution, metabolism, and excretion , collectively referred to as ADME , and is therefore a central consideration in the study of how molecules behave inside living systems.
In cannabinoid science, lipophilicity is particularly relevant. Cannabinoids such as THC and CBD carry high log P values (roughly 6–7), meaning they partition strongly into fatty tissue. This accounts for their affinity for the lipid-rich environment of the central nervous system, their extended residence in adipose tissue, and the prolonged detection windows observed in biological samples. Lipophilicity also contributes to the formulation challenges associated with delivering these compounds in oral or aqueous preparations.
Lipophilicity is distinct from , though related to; hydrophobicity. Hydrophobicity refers strictly to the tendency of a non-polar substance to repel water, whereas lipophilicity encompasses affinity for lipid media specifically. The distinction matters in precise pharmacokinetic and formulation contexts, even though the terms are sometimes used interchangeably in broader scientific literature.
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