What was the primary endpoint of the 4S trial?

All-cause mortality. The trial was specifically designed and powered to detect a difference in total deaths, not just cardiac events. This was a deliberate choice to address earlier concerns that cholesterol lowering might reduce heart attacks while increasing other causes of death.

How large was the mortality reduction with simvastatin in 4S?

Simvastatin reduced all-cause mortality by 30% (relative risk 0.70 to 95% CI 0.58-0.85, p = 0.0003). In absolute terms, 8.2% of patients on simvastatin died versus 11.5% on placebo over a median 5.4 years. The number needed to treat to prevent one death was approximately 30.

Did 4S show an increase in non-cardiovascular deaths?

No. Non-cardiovascular deaths were nearly identical: 49 in the simvastatin group versus 46 on placebo. Cancer deaths were 35 versus 33. This was a critical safety finding that dispelled prior concerns about non-cardiac mortality with cholesterol lowering.

How long did it take for the mortality benefit to appear?

The survival curves began separating at approximately 1.5 to 2 years. For major coronary events, divergence appeared earlier, around 12 months. The benefit continued to increase throughout the trial without reaching a plateau.

What dose of simvastatin was used in 4S?

All patients started on 20 mg daily. Those with total cholesterol still above 5.2 mmol/L at 6 weeks were titrated to 40 mg. About 37% of participants required the higher dose. The mean LDL reduction was 35%.

Did women benefit from simvastatin in the 4S trial?

Women made up only 19% of the trial (827 patients). The point estimate for major coronary events favored simvastatin (RR 0.66), but the confidence interval was wide. A later post-hoc analysis published in Circulation confirmed a significant reduction in major coronary events in women.

How did diabetic patients respond in 4S?

The 202 diabetic patients showed a 55% reduction in major coronary events (p = 0.002). Because their baseline event rate was higher, the absolute benefit was the largest of any subgroup. This finding helped establish statins as standard therapy in diabetic patients with CHD.

Was the 4S trial stopped early?

Yes. The Data Safety Monitoring Board stopped the trial because the mortality benefit had crossed the pre-specified stopping boundary. The median follow-up at termination was 5.4 years.

How does the 4S mortality reduction compare to other cardiovascular interventions?

The 30% relative mortality reduction is among the largest seen in cardiovascular trials. Beta-blockers post-MI reduce mortality by roughly 20%. Ramipril in HOPE showed 16%. The absolute benefit (NNT 30 over 5.4 years) is also favorable compared to most secondary prevention therapies.

Can 4S results be applied to primary prevention patients?

No. The trial enrolled only patients with established CHD (prior MI or angina) and elevated cholesterol. Primary prevention evidence came from later trials, including WOSCOPS (1995) and JUPITER (2008), which enrolled patients without prior cardiovascular events.

4S Results in Detail: Numbers, Subgroups, and Time Course

By HealthRX Medical Team

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

At a glance

Trial: Scandinavian Simvastatin Survival Study (4S)
N: 4,444 (2,221 simvastatin, 2,223 placebo)
Intervention: Simvastatin 20 mg/day, titrated to 40 mg if total cholesterol remained above 5.2 mmol/L
Comparator: Matching placebo
Duration: Median 5.4 years (range 4.9-6.3 years)
Primary endpoint: All-cause mortality
Key result: 30% relative risk reduction in all-cause mortality (p = 0.0003)

The Primary Endpoint: All-Cause Mortality

The 4S trial was the first randomized controlled trial powered to detect a mortality difference with a statin. Earlier lipid-lowering trials had shown reductions in coronary events but never a statistically significant drop in total deaths. The original 1994 Lancet publication reported 256 deaths in the placebo group (11.5%) versus 182 deaths in the simvastatin group (8.2%).

That 30% relative risk reduction (RR 0.70 to 95% CI 0.58-0.85) translated to an absolute risk reduction of 3.3 percentage points. The number needed to treat (NNT) to prevent one death over 5.4 years was approximately 30. For a secondary prevention population with baseline total cholesterol between 5.5 and 8.0 mmol/L, this was a clinically decisive result.

The p-value of 0.0003 comfortably crossed the pre-specified stopping boundary. The Data Safety Monitoring Board halted the trial early because the mortality benefit had become unambiguous.

Coronary Mortality and Major Coronary Events

Coronary deaths, the largest component of total mortality, fell by 42% (RR 0.58 to 95% CI 0.46-0.73). This was the primary driver of the all-cause mortality benefit. There were 189 coronary deaths in the placebo group compared with 111 in the simvastatin group.

Major coronary events (a composite of coronary death, non-fatal definite or probable myocardial infarction, and resuscitated cardiac arrest) showed a 34% relative risk reduction (RR 0.66 to 95% CI 0.59-0.75, p < 0.00001). The absolute rates were 28.0% for placebo versus 19.4% for simvastatin.

HealthRX Endpoint Hierarchy: 4S Results at a Glance

| Endpoint | Placebo (n=2,223) | Simvastatin (n=2,221) | RR (95% CI) | ARR | NNT (5.4 yr) | |---|---|---|---|---|---| | All-cause mortality | 256 (11.5%) | 182 (8.2%) | 0.70 (0.58-0.85) | 3.3% | 30 | | Coronary mortality | 189 (8.5%) | 111 (5.0%) | 0.58 (0.46-0.73) | 3.5% | 29 | | Major coronary events | 622 (28.0%) | 431 (19.4%) | 0.66 (0.59-0.75) | 8.6% | 12 | | Any coronary event | 742 (33.4%) | 548 (24.7%) | 0.70 (0.63-0.77) | 8.7% | 12 | | Revascularization (CABG/PTCA) | 383 (17.2%) | 252 (11.3%) | 0.63 (0.54-0.74) | 5.9% | 17 | | Cerebrovascular events | 70 (3.1%) | 47 (2.1%) | 0.65 (0.45-0.95) | 1.0% | 100 |

This table organizes the full 4S endpoint set by clinical weight, from mortality through revascularization and stroke. The consistent direction across every endpoint, with no single outlier trending toward harm, was what made the trial conclusive for regulators and guideline committees.

Non-Cardiovascular Death: The Safety Signal That Wasn't

Earlier meta-analyses of fibrate and cholestyramine trials had raised concerns that lowering cholesterol might increase non-cardiovascular mortality, particularly from cancer, trauma, and suicide. The 4S investigators pre-specified this as a safety analysis.

Non-cardiovascular deaths were nearly identical between groups: 49 in the simvastatin arm versus 46 in the placebo arm. Cancer deaths specifically numbered 35 versus 33. This null finding was critical. It allowed the FDA to approve simvastatin's coronary mortality indication without the cloud of excess non-cardiac death that had dogged earlier lipid drugs.

Lipid Changes: Median Reductions and Dose Titration

Participants entered with total cholesterol between 5.5 and 8.0 mmol/L (approximately 213-309 mg/dL) and triglycerides <2.5 mmol/L. At baseline, mean LDL cholesterol was 4.87 mmol/L (188 mg/dL).

All patients started on 20 mg/day. At 6 weeks, those with total cholesterol still above 5.2 mmol/L were titrated to 40 mg. Approximately 37% of the simvastatin group required the higher dose.

On-treatment lipid changes in the simvastatin arm:

| Lipid Parameter | Mean Change from Baseline | |---|---| | Total cholesterol | -25% | | LDL cholesterol | -35% | | HDL cholesterol | +8% | | Triglycerides | -10% |

The placebo group showed essentially no change in lipid values over the trial. The 35% LDL reduction is modest by current standards (high-intensity statins achieve 50%+), but it was sufficient to produce a mortality benefit in this high-risk population. This dose-response relationship later informed the 2013 ACC/AHA cholesterol guidelines, which shifted focus from LDL targets to statin intensity.

Time Course of Benefit

The Kaplan-Meier survival curves for all-cause mortality began separating visibly at approximately 1.5 to 2 years. For major coronary events, the divergence appeared earlier, around 12 months. This lag is consistent with the biology: LDL lowering begins within weeks, but plaque stabilization and regression require months of sustained exposure.

By year 3, the mortality curves had clearly separated. By year 5, the gap continued to widen without any plateau, suggesting that longer treatment would have produced even greater absolute benefit. This observation was later confirmed by the Heart Protection Study and other long-duration statin trials.

The absence of early harm is worth noting. Some interventions show an initial hazard before a delayed benefit (as seen with certain antiarrhythmics). Simvastatin showed no such early crossover. Mortality in the simvastatin group was never higher than placebo at any time point during follow-up.

Subgroup Analyses

The 4S investigators reported pre-specified subgroup analyses across age, sex, baseline cholesterol, diabetes status, and hypertension. The consistency of benefit was striking.

Age: Patients 60 years and older (n = 1,021) derived the same relative risk reduction as younger patients. Absolute benefit was actually larger in older patients because their baseline event rate was higher.

Sex: Women comprised only 19% of the trial (n = 827). The point estimate for major coronary events in women favored simvastatin (RR 0.66), but the confidence interval was wide due to limited statistical power. A later post-hoc analysis of the female subgroup published in Circulation confirmed a significant reduction in major coronary events.

Diabetes: A subgroup analysis of the 202 diabetic patients showed a 55% reduction in major coronary events (p = 0.002). The absolute risk reduction was largest in this subgroup because diabetic patients had the highest baseline event rate. This finding helped establish the evidence base that led to near-universal statin recommendation in diabetic patients with CHD.

Baseline LDL: Patients in both the upper and lower halves of the baseline LDL distribution benefited. There was no threshold below which simvastatin stopped working within the trial's entry range.

Ejection fraction and heart failure history were not systematically collected, which limits interpretation for patients with reduced cardiac function.

What the Trial Did Not Show

The 4S population was narrow by design: ages 35-70, established CHD (prior MI or angina), elevated but not extreme cholesterol, excluded if triglycerides exceeded 2.5 mmol/L. The trial did not enroll primary prevention patients, did not study patients with normal cholesterol levels, and excluded those with heart failure or unstable angina.

The investigators acknowledged several limitations. Concomitant aspirin use was not standardized, though approximately 37% of both groups used aspirin. ACE inhibitor and beta-blocker use was similarly uncontrolled but balanced between arms. The trial predated widespread use of coronary stenting, so revascularization patterns reflected a different procedural era.

The relatively homogeneous Scandinavian population (overwhelmingly white, Northern European) limits direct extrapolation to other ethnic groups. Subsequent trials like ALLHAT-LLT and the Heart Protection Study enrolled more diverse populations and confirmed statin benefit across racial groups, though 4S itself cannot make that claim.

Putting the Numbers in Context

A 30% relative mortality reduction is large by cardiovascular trial standards. For comparison, the HOPE trial for ramipril showed a 16% mortality reduction. Beta-blockers after MI reduce mortality by approximately 20%. Aspirin in secondary prevention reduces vascular events by about 25% but has a smaller effect on total mortality.

The NNT of 30 over 5.4 years means that for every 30 patients treated, one death was prevented. In the subgroup with the highest baseline risk (diabetic patients with prior MI), the NNT was substantially lower, likely in the range of 12-15 based on the subgroup event rates.

The 4S trial changed clinical practice more decisively than any single cardiovascular RCT before it. Within two years of publication, statin prescribing in secondary prevention populations increased several-fold. The trial's mortality result removed the primary objection to cholesterol lowering, namely that reducing cardiac death might be offset by non-cardiac death, and established the evidence foundation that every subsequent statin trial built upon.

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