How long did patients in ODYSSEY OUTCOMES actually receive alirocumab?

The median treatment duration was 2.8 years, but individual patients received alirocumab for anywhere from a few months to approximately 5 years. The event-driven design meant that early enrollees had longer exposure than late enrollees.

Did the MACE benefit of alirocumab grow over time?

Yes. The Kaplan-Meier curves for the primary composite continued to diverge beyond year 2, suggesting a cumulative benefit with sustained LDL-C lowering. This pattern was most pronounced in patients with baseline LDL-C ≥ 100 mg/dL.

Was there a formal open-label extension of ODYSSEY OUTCOMES?

No. Unlike some cardiovascular trials that transitioned to open-label treatment, ODYSSEY OUTCOMES did not have a published formal extension study. Post-trial observation was limited to the variable blinded treatment period.

Did alirocumab reduce all-cause mortality in ODYSSEY OUTCOMES?

Nominally, yes (HR 0.85, p = 0.026). However, the mortality endpoint was not adjusted for multiple comparisons under the pre-specified statistical hierarchy, so the result does not meet the conventional threshold for confirmatory evidence.

Were there neurocognitive safety concerns with very low LDL-C in ODYSSEY OUTCOMES?

No. Neurocognitive adverse events were not increased with alirocumab, even in patients whose LDL-C fell below 25 mg/dL. This is consistent with findings from the EBBINGHAUS cognitive substudy of the FOURIER trial.

What happened to LDL-C levels after alirocumab was stopped?

LDL-C returned toward pre-treatment levels within weeks of discontinuation, consistent with the drug's mechanism of action. PCSK9 inhibitors do not permanently alter LDL receptor biology.

How does ODYSSEY OUTCOMES compare to FOURIER in terms of long-term data?

ODYSSEY OUTCOMES had a longer median follow-up (2.8 vs. 2.2 years), enrolled a higher-risk post-ACS population, and showed a nominal mortality signal that FOURIER did not. Neither trial has published a multi-year post-trial follow-up comparable to long-term statin studies.

Did ODYSSEY OUTCOMES affect guideline recommendations for PCSK9 inhibitors?

Yes. The 2018 ACC/AHA cholesterol guidelines gave a Class IIa recommendation for adding PCSK9 inhibitors in patients with recent ACS on maximally tolerated statins whose LDL-C remains ≥ 70 mg/dL, supported in part by the ODYSSEY OUTCOMES data.

Why did some alirocumab patients get switched to placebo during the trial?

The blinded titration protocol switched patients to placebo if their LDL-C fell below 15 mg/dL on two consecutive measurements. This affected about 7.7% of alirocumab-treated patients and was designed to limit exposure to extremely low LDL-C levels.

Is alirocumab still available after the ODYSSEY OUTCOMES trial?

Yes. Alirocumab (brand name Praluent) remains FDA-approved for LDL-C reduction and cardiovascular risk reduction. Its list price was reduced by roughly 60% in 2019 following the outcomes data and payer negotiations.

ODYSSEY OUTCOMES Extension Data and What Happened After the Trial Ended

By HealthRX Medical Team

Published May 25, 2026Updated May 25, 2026Last reviewed May 25, 2026

At a glance

| Parameter | Detail | |---|---| | N | 18,924 | | Intervention | Alirocumab 75 mg or 150 mg SC every 2 weeks | | Comparator | Matching placebo | | Duration | Median 2.8 years (range up to 5 years) | | Primary endpoint | Composite MACE (coronary heart disease death, nonfatal MI, fatal or nonfatal ischemic stroke, unstable angina requiring hospitalization) | | Key result | HR 0.85 (95% CI 0.78, 0.93; p < 0.001) for primary MACE composite | | LDL reduction | Alirocumab group achieved median LDL-C of 53 mg/dL at month 4 vs. 101 mg/dL with placebo |

Why the Primary Publication Was Not the Full Story

The primary ODYSSEY OUTCOMES publication reported results from a median follow-up of 2.8 years, but the trial protocol allowed treatment and observation for up to 5 years. Because the trial used an event-driven design (1,613 primary endpoint events triggered the final analysis), many patients were still on blinded treatment when the study was stopped. This created a population with variable exposure durations, and the longer-treated patients carried information the headline hazard ratio could not fully capture.

Several pre-specified and post-hoc analyses examined what happened with extended exposure. These analyses matter because PCSK9 inhibitors were still relatively new biologics, and both regulators and payers wanted evidence that the cardiovascular benefit persisted (or grew) rather than fading, and that safety remained acceptable beyond two years.

Time-Dependent Treatment Effect: The Benefit Was Not Static

One of the most clinically significant findings from extended analysis was that the alirocumab benefit appeared to increase with longer treatment duration. In the primary trial report, the Kaplan-Meier curves for the composite MACE endpoint began separating around 12 months and continued to diverge through the observation period.

HealthRX Durability-of-Effect Framework for ODYSSEY OUTCOMES

When evaluating whether a cardiovascular drug's benefit is durable, three patterns matter:

| Pattern | What It Means | ODYSSEY OUTCOMES Evidence | |---|---|---| | Curve convergence | Benefit fades after drug is stopped | Not observed during trial | | Parallel curves | Benefit is stable but does not grow | Observed in years 1, 2 | | Continued divergence | Cumulative benefit increases with longer exposure | Observed after year 2 |

The ODYSSEY OUTCOMES data fit the third pattern. In pre-specified landmark analyses, the absolute risk reduction for the primary composite was approximately 1.6 percentage points at the final analysis, but among patients with baseline LDL-C ≥ 100 mg/dL, the absolute reduction reached 3.4 percentage points. This subgroup (roughly one-quarter of the trial) also showed the clearest signal for all-cause mortality benefit (HR 0.71 to 95% CI 0.56, 0.90), as reported in a pre-specified analysis published alongside the primary results.

The time-dependent growth in benefit aligns with the atherosclerosis biology: sustained LDL-C lowering is expected to produce cumulative plaque stabilization and regression, a process measured in months and years rather than weeks.

The All-Cause Mortality Signal: Still Debated

ODYSSEY OUTCOMES produced a nominal reduction in all-cause mortality (HR 0.85 to 95% CI 0.73, 0.98, nominal p = 0.026). The word "nominal" is important here. The statistical analysis plan reserved alpha spending for the primary composite, so the mortality result was not adjusted for multiplicity and does not meet the conventional bar for statistical significance in a confirmatory sense.

This finding is unusual in modern cardiovascular trials. Most statin add-on trials (ezetimibe in IMPROVE-IT, for example) have not shown mortality reduction. The FOURIER trial of evolocumab, the other approved PCSK9 inhibitor, showed no mortality signal at all (HR 1.04 for cardiovascular death) over a shorter median follow-up of 2.2 years.

Several hypotheses have been discussed in subsequent literature:

Longer exposure window. ODYSSEY OUTCOMES had a longer median follow-up than FOURIER, potentially allowing more time for the mortality benefit of deep LDL-C lowering to manifest.
Post-ACS population. ODYSSEY enrolled patients within 1 to 12 months of an ACS event. This is a higher-risk window than the stable atherosclerotic disease population in FOURIER, meaning the absolute benefit of intervention is larger.
LDL-C titration protocol. The ODYSSEY design blinded dose adjustments and discontinued alirocumab (replaced with placebo) when LDL-C fell below 15 mg/dL for two consecutive measurements. This may have reduced adverse events related to extremely low LDL-C.

No dedicated extension study was conducted to resolve the mortality question definitively. The 2018 ACC/AHA cholesterol guideline update acknowledged the ODYSSEY OUTCOMES results but stopped short of recommending PCSK9 inhibitors specifically for mortality reduction.

Safety Beyond the Primary Analysis Window

Neurocognitive Events

A major concern before and during the PCSK9 inhibitor era was whether very low LDL-C levels could impair neurocognitive function. LDL-C is a precursor for central nervous system cholesterol synthesis (though the blood-brain barrier largely separates peripheral and CNS cholesterol pools). ODYSSEY OUTCOMES included pre-specified neurocognitive adverse event monitoring.

Results through the full observation period:

| Neurocognitive endpoint | Alirocumab (n = 9,462) | Placebo (n = 9,462) | |---|---|---| | Any neurocognitive event | 1.5% | 1.8% | | Memory impairment | 0.5% | 0.7% | | Confusional state | 0.3% | 0.4% | | Dementia | 0.1% | 0.1% |

No increase in neurocognitive events was seen with alirocumab, even among the subset of patients whose LDL-C fell below 25 mg/dL. This was consistent with the EBBINGHAUS substudy of FOURIER, which used formal cognitive testing and found no difference between evolocumab and placebo groups.

New-Onset Diabetes

Statins carry a well-characterized risk of new-onset diabetes, raising the question of whether PCSK9 inhibitors add to this risk. In ODYSSEY OUTCOMES, new-onset diabetes occurred in 9.6% of alirocumab-treated patients vs. 10.1% of placebo patients among those without diabetes at baseline. There was no signal of increased diabetic risk. Mendelian randomization studies of PCSK9 loss-of-function variants had suggested a possible link, but the trial data did not confirm this at clinically relevant exposure durations.

Injection-Site Reactions and Discontinuation

Over the full treatment period, injection-site reactions were more common with alirocumab (3.8% vs. 2.1% with placebo). These were overwhelmingly mild and rarely led to discontinuation. The overall discontinuation rate due to adverse events was 4.8% for alirocumab vs. 4.7% for placebo, a negligible difference over years of subcutaneous injections every two weeks.

Hepatic and Muscular Safety

Liver enzyme elevations (ALT >3x upper limit of normal) occurred in 1.6% of both groups. Myalgia and rhabdomyolysis rates were similar. Since all patients were already on high-intensity statins, these findings confirmed that adding alirocumab did not compound statin-related hepatic or muscular toxicity. The Praluent prescribing information reflects this safety profile.

The LDL-C Titration Protocol and Its Implications

ODYSSEY OUTCOMES used a unique blinded dose-titration algorithm. Patients started on alirocumab 75 mg every two weeks. At week 8, if LDL-C was ≥ 50 mg/dL, the dose was increased to 150 mg. If LDL-C fell below 25 mg/dL on consecutive measurements, patients were switched to placebo (while remaining blinded). Roughly 7.7% of alirocumab patients were switched to placebo through this mechanism.

This protocol had real consequences for the trial's interpretation. The intention-to-treat analysis included patients who were effectively on placebo for part of the study in the alirocumab arm, which diluted the observed treatment effect. Some researchers have argued that the "on-treatment" effect of alirocumab is larger than the 15% relative risk reduction reported in the primary publication.

The titration design also set ODYSSEY apart from FOURIER, which used fixed dosing. The ODYSSEY approach was more conservative and arguably more reflective of how clinicians would manage LDL-C targets in practice, titrating to a goal rather than prescribing a fixed maximum dose.

What Post-Trial Observation Showed About Regression to Mean

After the blinded treatment period ended, patients who had been on alirocumab saw their LDL-C rise back toward baseline levels within weeks of discontinuation. PCSK9 inhibitors do not modify the underlying biology of LDL receptor recycling permanently. They work only while present in circulation, and alirocumab has a half-life of approximately 17 to 20 days at steady state.

This "rebound" raised practical questions. If the cardiovascular benefit depends on sustained LDL-C lowering, does stopping treatment erase the gains? The available data suggest that events prevented during the treatment period remain prevented. The Kaplan-Meier curves did not converge after treatment cessation in the trial's observation window, consistent with the idea that plaque stabilization achieved during treatment is not immediately reversed. Similar observations have been made with statins in the post-trial follow-up of the WOSCOPS study, where statin benefits persisted years after the trial ended.

Still, the lack of a formal long-term post-trial extension (comparable to the 10-year ASCOT-LLA or 20-year WOSCOPS follow-ups) limits what we can say about very long-term outcomes after PCSK9 inhibitor discontinuation.

How ODYSSEY OUTCOMES Changed Clinical Practice

The 2018 ACC/AHA multisociety guideline on blood cholesterol management incorporated ODYSSEY OUTCOMES data into its recommendations. For patients with recent ACS on maximally tolerated statins (plus ezetimibe if needed) whose LDL-C remains ≥ 70 mg/dL, a PCSK9 inhibitor is a Class IIa recommendation (reasonable to add). The 2022 ACC Expert Consensus Decision Pathway further lowered the threshold for considering PCSK9 inhibitors in very-high-risk patients.

From a payer perspective, ODYSSEY OUTCOMES was the second large outcomes trial (after FOURIER) confirming PCSK9 inhibitor cardiovascular benefit. The cumulative evidence shifted the conversation from "do these drugs work?" to "how do we afford them for the right patients?" Sanofi and Regeneron subsequently reduced the list price of alirocumab by approximately 60% in 2019, a move directly tied to the outcomes evidence and payer negotiations.

Limitations of the Follow-Up Data

Several gaps remain. No formal open-label extension study was published for ODYSSEY OUTCOMES. The variable treatment duration (patients were on study drug for anywhere from a few months to 5 years) makes it difficult to isolate the effect of treatment duration from the effect of time-on-study. The trial population was predominantly white (77.6%) and male (74.6%), limiting generalizability to underrepresented populations. The post-ACS setting means the results cannot be directly extrapolated to primary prevention or to patients with stable coronary disease without recent events.

The titration-to-placebo design, while clinically pragmatic, introduced complexity into the intention-to-treat analysis that makes direct comparison with fixed-dose trials like FOURIER imprecise.

Frequently asked questions

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References

Schwartz GG, Steg PG, Szarek M, et al. Alirocumab and Cardiovascular Outcomes after Acute Coronary Syndrome. N Engl J Med. 2018;379(22):2097-2107. PubMed
Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol. J Am Coll Cardiol. 2019;73(24):e285-e350. PubMed
Sabatine MS, Giugliano RP, Keech AC, et al. Evolocumab and Clinical Outcomes in Patients with Cardiovascular Disease. N Engl J Med. 2017;376(18):1713-1722. PubMed
Praluent (alirocumab) Prescribing Information. Sanofi/Regeneron Pharmaceuticals. FDA Label
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Cannon CP, Blazing MA, Giugliano RP, et al. Ezetimibe Added to Statin Therapy after Acute Coronary Syndromes. N Engl J Med. 2015;372(25):2387-2397. PubMed