Arrowhead’s RNA Drug Cut Triglycerides ~80% and Slashed Pancreatitis in Phase 3

Arrowhead Pharmaceuticals’ experimental drug plozasiran produced striking Phase 3 results in severe hypertriglyceridemia (sHTG) — dangerously high blood fats that can trigger acute pancreatitis.

In the SHASTA-3 and SHASTA-4 studies, plozasiran delivered median triglyceride reductions of 79% and 81% at 12 months, and cut acute pancreatitis events by 78% overall — and by 100% in the highest-risk patients. The data were presented as a late-breaker at ESC Congress 2026.

Why very high triglycerides are an emergency risk

Triglycerides are the main form in which fat circulates and is stored. Mildly raised levels are a cardiovascular risk marker. Extremely raised levels are a different problem entirely.

Above roughly 1,000 mg/dL, the blood carries so many triglyceride-rich particles that it can become visibly milky, and the risk of acute pancreatitis rises sharply. Pancreatic enzymes activate within the pancreas itself and begin digesting the organ — an intensely painful condition that can progress to necrosis, organ failure and death.

Recurrent attacks compound the damage, and patients living with sHTG often organise their lives around avoiding the next one. This is not a risk-factor management problem; it is prevention of an acute, disabling event.

Why existing treatments are inadequate

Statins, the dominant lipid drugs, primarily lower LDL cholesterol and do relatively little for triglycerides at these levels. Fibrates and omega-3 preparations help modestly. Extremely restricted low-fat diets are prescribed and are difficult to sustain.

For patients whose triglycerides remain dangerous on all of it, options effectively run out — which is why an 80% reduction is a categorical rather than incremental change.

How plozasiran works

Plozasiran is an RNA interference therapy, an injectable that silences the gene for APOC3.

APOC3 is a protein that inhibits triglyceride clearance — it blocks the enzyme responsible for breaking down triglyceride-rich particles in the bloodstream. Reducing APOC3 removes that brake, letting the body clear triglycerides through its own machinery.

The genetic evidence behind the target is unusually strong. People carrying naturally inactivating APOC3 variants have low triglycerides and reduced cardiovascular risk, with no apparent harm from the deficiency — close to a natural demonstration that removing APOC3 is both effective and safe.

RNAi therapies work by degrading the messenger RNA for a target protein before it is translated. Delivered to the liver, where APOC3 is made, they can be dosed infrequently because the silencing effect persists.

The result that actually matters

The triglyceride numbers are impressive; the pancreatitis numbers are the ones that count.

Lipid drugs are routinely approved on biomarker changes, and recent history — a lipoprotein(a) drug that lowered its target and prevented nothing, an anti-inflammatory that suppressed its biomarker without reducing events — is a standing warning about that inference.

Here the trial measured the clinical event itself. A 78% reduction in acute pancreatitis, rising to 100% in the highest-risk group, is evidence that lowering triglycerides in this population prevents the thing patients actually fear. That closes the loop that other lipid programmes have left open.

Safety

Arrowhead reported no new safety signals, with favourable liver, hypersensitivity and platelet profiles. Three deaths occurred among treated patients — two cardiovascular, one from a blood cancer — all attributed to pre-existing disease and assessed as unrelated to the drug.

Deaths in a trial always warrant scrutiny, and independent adjudication of causality is the appropriate process. In a population with substantial baseline cardiovascular and metabolic disease, some events are expected regardless of treatment.

The competitive picture

Plozasiran is not alone. The APOC3 pathway has attracted several programmes, and a drug targeting the same protein has already reached the market for familial chylomicronemia syndrome — the rare genetic extreme of this spectrum, where patients cannot clear triglycerides at all.

Severe hypertriglyceridemia more broadly is a substantially larger population than FCS, which is what makes it the commercially decisive indication. Competition here will turn on the depth and durability of triglyceride lowering, dosing frequency, and whichever programme can show hard event reduction most convincingly.

What comes next

Arrowhead plans to file a supplemental NDA in the US before the end of 2026.

Who these patients are

Severe hypertriglyceridemia is not simply the top end of a normal distribution. It usually reflects an underlying impairment in the machinery that clears triglyceride-rich particles from blood, frequently with a genetic component, amplified by factors such as poorly controlled diabetes, alcohol, obesity, pregnancy or certain medications.

That distinction matters for who benefits. Someone with moderately raised triglycerides and no clearance defect is a cardiovascular risk-management problem addressed largely through lifestyle and treating the underlying condition. Someone whose triglycerides sit in the thousands despite maximal conventional therapy has a mechanical failure of clearance, and no amount of dietary restriction reliably compensates.

It is the second group for whom an APOC3-targeted drug is transformative rather than incremental, because it acts on the clearance mechanism itself. It is also why pancreatitis prevention, rather than cardiovascular risk reduction, is the endpoint that defines the indication.

These are topline Phase 3 data presented at a conference. Full peer-reviewed publication will allow proper scrutiny of the pancreatitis adjudication — how events were defined and confirmed matters greatly when it is the primary clinical claim — and the durability of effect beyond 12 months remains to be characterised for what would be a lifelong therapy. Clinical trial news, not medical advice.