Moisture is one of the most prevalent risks to pharmaceutical stability. From oral solid dosage (OSD) forms such as tablets and capsules to inhalation devices, f luctuations in humidity can compromise drug quality, alter dissolution profiles, and shorten shelf life. Excess moisture can catalyze hydrolytic degradation or polymorphic changes, while overly dry conditions may cause excipients and gelatin capsules to lose mechanical integrity.

Traditionally, packaging has relied on desiccants such as silica gel and molecular sieve to mitigate moisture ingress. These technologies remain widely used and effective in many applications. However, their inherent adsorption behaviours – either too gradual or too aggressive – do not always align with the specific needs of modern drug products. This has prompted interest in engineered equilibrium systems designed to maintain a target relative humidity (RH) rather than simply reducing it as far as possible.

This article reviews the strengths and limitations of silica gel and molecular sieve, and explores the role of equilibrium humidity stabilisers, such as EQIUS®, in balancing product stability with packaging efficiency