The Hidden Cost of "Just-in-Case" Inventory in Clinical Trials

Nobody ever got called into a meeting to explain why there was too much drug.

That single asymmetry explains most of the excess inventory in clinical supply. A stockout is visible, urgent, and attributable — a patient missed a dose, and someone has to answer for it. Overage is invisible, gradual, and blameless. It shows up as a line in a manufacturing budget, some storage costs, and eventually a destruction certificate that nobody reads.

So supply teams do the rational thing given the incentives: they build a buffer, and then they build a buffer on the buffer. It feels like prudence. Under the traditional just-in-case model, end-of-trial waste has been estimated at 50–60% of the drug produced. That's not prudence. That's a cost structure nobody chose deliberately.

Where the cost actually hides

The reason over-supply survives scrutiny is that its cost is distributed across half a dozen budget lines, none of which look alarming alone.

Manufacturing cost. The most obvious. Every unit made is paid for, and for biologics and comparators, unit costs are substantial. Where comparators are involved, they can account for a very large share of total clinical supply spend — and every point of unnecessary overage multiplies against that price.

Manufacturing capacity. Less obvious and often more valuable. A production slot used to make drug you'll destroy is a slot unavailable to another program. For organizations with constrained capacity, this is the real cost, and it never appears in the trial's budget.

Packaging and labeling. Excess material gets packaged and labeled too, at full cost, including the multi-language booklet labeling that global trials require.

Storage and distribution. Every extra kit occupies cold-chain or ambient storage for the duration, gets shipped, sometimes gets shipped again, and is counted, reconciled, and monitored throughout.

Expiry replacement. This one compounds. Over-supplied stock ages, expires before it's used, and is replaced — so you pay for the same coverage twice, sometimes three times over the life of a long study.

Destruction and reconciliation. At close-out, unused product must be returned, reconciled, and destroyed under controlled conditions. Disposal is a cost, not a saving.

Stranded inventory. The quiet one. Supply labeled or positioned for a country that under-enrolls can't easily move. It isn't destroyed because it expired; it's destroyed because it was in the wrong place with the wrong label.

Why "just add 30%" persists

Rules of thumb survive because they're fast, defensible in a meeting, and superficially safe. Nobody has ever been criticized for a buffer that turned out to be unnecessary.

But a blanket percentage is wrong in both directions simultaneously. It over-supplies the stable, predictable parts of your trial — the large sites with steady enrollment, the low-variability arms — while under-supplying the genuinely volatile ones: the newly activated site, the country with erratic customs, the arm with high titration. A flat buffer distributes protection evenly across risks that are not evenly distributed. You end up carrying waste and residual stockout risk at the same time.

The alternative: buy protection where the risk actually is

The shift is from "how much extra should we make?" to "where is our supply actually at risk, and how much cover does that require?"

In practice this means:

• Model demand uncertainty explicitly, using simulation across enrollment speed, drop-out, and randomization rather than a single deterministic forecast.
• Set a target service level and supply to it — enough to avoid a stockout in the large majority of plausible scenarios, quantified rather than guessed.
• Vary buffers by risk, holding more cover where variability, lead times, or consequences are highest and less where they're low.
• Use pooling and flexible labeling so a single unit of buffer can protect several countries at once instead of one.
• Re-forecast continuously against real enrollment and dispensing data, and release excess early enough to matter.
• Align sourcing frequency with shelf life, so you're not replacing expiring stock more often than necessary.

The result isn't less protection. It's the same or better protection, concentrated where it does something.

The leadership problem underneath

This is ultimately a governance issue more than a technical one. If your organization only ever reviews stockouts, you will get over-supply — reliably, forever, because that's what the incentives reward.

The fix is to make overage visible at the same level as stockouts. Report projected end-of-trial waste alongside service level. Ask what the buffer is protecting against and what it costs. Treat a 55% destruction rate as a result worth explaining, not a routine close-out activity. Leaders get the supply chain their metrics ask for.