Attempts to perform Pasteurian resolution on epinephrine (or adrenaline) hydrogeno-tartrate always lead to limited enrichments in (-)-epinephrine. Structural and thermal investigations are performed on the diastereomeric system to understand this behavior. The analyses revealed the existence of a (metastable) total solid solution between the two anhydrous diastereomeric salts. This solid solution is partially inhibited by the crystallization of a stable hydrate; nevertheless, its extension still prevents high enrichment by single-step crystallization. Phase diagrams are proposed to illustrate this non-favored and non-predictable behavior.