Stability of softgels and tablets: what degrades and how it is tested

What degrades in a softgel

A softgel fails in one of two places: the fill oxidises, or the shell changes. Oil oxidation is measured by peroxide value and p-anisidine value; the two together give the TOTOX value. Shell change shows up as cross-linking, brittleness, stickiness or leakage, and it is driven by moisture, temperature and the plasticiser.

• Oxidation — fish oil and black seed oil are the most sensitive fills; oregano oil is volatile as well as oxidisable. Nitrogen flushing and an opaque shell are the first controls.
• Shell cross-linking — gelatin reacts with aldehydes from oxidised fill or with residual moisture. It shows up as a slower disintegration and a harder shell.
• Moisture — a softgel shell picks up water from humid air and loses it to dry air. Both directions change hardness and seam strength.
• Light — clear shells transmit light into the fill. Opaque shells and opaque bottles are the control.

What degrades in a tablet

A tablet fails through moisture, hydrolysis or physical change. The coating is the first barrier; the bottle and the desiccant are the second. Hardness and disintegration are the early indicators, because they move before the assay does.

• Moisture uptake — hygroscopic extracts such as shilajit pick up water, soften and then stick. Film coating and a desiccant are the standard controls.
• Hydrolysis — SAMe is the clear case in this category; the enteric coat and a moisture barrier are part of the release specification.
• Hardness drift — granulation moisture and compression force move hardness. A tablet that hardens on storage may fail disintegration.
• Colour and appearance — algae tablets fade; mineral tablets can mottle. A colour range and a retention sample are useful if appearance is a label claim.

The ICH protocol we run

Stability is run on the finished dosage form in its commercial pack. The standard protocol follows ICH Q1A: long-term, intermediate and accelerated conditions, with the timepoints below. The exact matrix is agreed with the product and the market.

The tests at each timepoint are the release tests plus appearance: marker assay, moisture, hardness or disintegration, peroxide value for oils, and microbial limits at the start and the end. A stability report that lists only the assay is not a stability report.

Packaging is part of the data

The same tablet can pass 24 months in one pack and fail in another. The stability protocol therefore runs on the commercial pack, not on a generic container.

• HDPE bottle — the default for retail counts. An induction seal and a desiccant canister are added for moisture-sensitive products.
• Blister — a better moisture barrier per dose, but a higher unit count and a different tooling set.
• Bulk drum — a liner and a desiccant for bulk tablets and softgels; the drum is opened repeatedly, so the in-use stability is shorter.
• Nitrogen — used for oils and for bulk powders; it displaces oxygen before the container is sealed.

Marker-specific risks

These are the failure modes we see most often. They are not the only ones; the product specification and the destination market decide the final protocol.

What the shelf-life claim means

A 24-month shelf life is a claim supported by real-time data on the commercial pack. Accelerated data underpins the claim but does not replace the real-time study. If your market requires a shorter or longer claim, the protocol and the packaging are adjusted before the batch, not after.

Product-specific notes

Each row maps one product in this range to the parameter this document controls. The product pages link back to their own row; when you compare two products, compare the method column before the number.