How many people were in the 4S trial?

The trial randomized 4,444 patients with established coronary heart disease across 94 clinical centers in five Scandinavian countries between 1988 and 1994.

What drug was tested in the 4S trial?

Simvastatin, an HMG-CoA reductase inhibitor (statin), at doses of 20 to 40 mg daily. It was later marketed as Zocor by Merck.

What was the main finding of the 4S trial?

Simvastatin reduced all-cause mortality by 30% compared to placebo over a median follow-up of 5.4 years. This was the first randomized trial to demonstrate that a statin could prevent death.

Did the 4S trial include women?

Yes, but women comprised only 19% of the study population. The mortality benefit did not reach statistical significance in the female subgroup alone, though the trend was consistent with the overall result.

What cholesterol level did patients need to enter the 4S trial?

Participants needed a total cholesterol between 5.5 and 8.0 mmol/L (approximately 213 to 310 mg/dL) after eight weeks of dietary modification. These are moderate-to-high levels by current standards.

Were there serious side effects in the 4S trial?

Serious adverse events were rare. There was no increase in cancer, no reported rhabdomyolysis, and liver enzyme elevations were similar between groups. The safety profile was a major reason regulators approved simvastatin for mortality reduction.

What is the NNT from the 4S trial?

Approximately 30. This means that treating 30 CHD patients with simvastatin for about 5.4 years prevented one additional death. For cardiovascular trials targeting mortality, this is considered a strong result.

How did 4S change medical practice?

Before 4S, cholesterol-lowering drugs lacked proof of a survival benefit. After 4S, statins became standard therapy for secondary prevention in heart disease. This directly influenced ACC/AHA guidelines that remain in effect today.

Is simvastatin still used today?

Yes, though it has been largely supplanted by atorvastatin and rosuvastatin for high-intensity therapy. Current guidelines favor these newer statins because they achieve greater LDL reductions at standard doses.

Did the 4S trial look at stroke risk?

Cerebrovascular events were a secondary endpoint. Simvastatin reduced them by 30% (p = 0.024), providing early evidence that statins protect beyond the coronary arteries.

4S Trial: A Plain-English Overview of What It Established

By HealthRX Medical Team

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

At a glance

| Detail | Value | |---|---| | Full name | Scandinavian Simvastatin Survival Study (4S) | | N | 4,444 | | Intervention | Simvastatin 20 mg daily, titrated to 40 mg if total cholesterol remained above 5.2 mmol/L | | Comparator | Matching placebo | | Median follow-up | 5.4 years | | Primary endpoint | All-cause mortality | | Key result | 30% relative risk reduction in all-cause mortality (RR 0.70 to 95% CI 0.58, 0.85, p = 0.0003) | | Publication | The Lancet, November 1994 |

The question the trial asked

Before 1994, physicians knew that people with high cholesterol died more often from heart attacks. What they did not know was whether lowering that cholesterol with medication would actually prevent death. Earlier drug trials using fibrates and resins had reduced cholesterol but failed to show a survival benefit, and some raised concern about increases in non-cardiac deaths. The 4S investigators designed a trial to answer a single, stark question: does simvastatin reduce the chance of dying, from any cause, in patients who already have coronary heart disease (CHD)?

That distinction matters. The primary endpoint was not "fewer heart attacks" or "lower LDL on a lab slip." It was death. The trial was powered specifically to detect a mortality difference, which required both a large sample and a long follow-up.

Who was enrolled

The trial recruited men aged 35 to 69 and women aged 35 to 70 across 94 centers in Denmark, Finland, Iceland, Norway, and Sweden between 1988 and 1989. Every participant had a documented history of angina pectoris or a prior myocardial infarction (MI). Their baseline total cholesterol had to fall between 5.5 and 8.0 mmol/L (roughly 213 to 310 mg/dL) after eight weeks on a lipid-lowering diet.

Key exclusions: unstable angina, planned bypass surgery, secondary hyperlipidemia, and premenopausal women not using contraception. The population was overwhelmingly white and Scandinavian, which limits generalizability to other ethnic groups. The mean age was 58, roughly 19% of participants were women, and 79% had a prior MI at baseline, as reported in the primary publication.

How the trial actually worked

Dose titration, not a fixed dose

After a diet-only run-in, participants were randomized 1:1 to simvastatin or placebo. The starting dose was 20 mg once daily in the evening. At 12 and 24 weeks, if total cholesterol remained above 5.2 mmol/L, the dose was doubled to 40 mg. About 37% of patients in the simvastatin arm needed that uptitration. This titrate-to-target design reflected real clinical practice more accurately than a fixed-dose approach.

Blinding and compliance

The trial was double-blind. Compliance was tracked by pill counts. Over the 5.4-year median follow-up, the dropout rate was low by modern standards: roughly 10% in the simvastatin group and 13% in the placebo group discontinued study medication. The investigators used intention-to-treat analysis, meaning every randomized patient counted toward the final result regardless of whether they kept taking the pills.

What was measured

The primary endpoint was total mortality. Pre-specified secondary endpoints included coronary death, major coronary events (coronary death plus non-fatal MI), and the need for revascularization procedures (bypass grafting or angioplasty). Safety monitoring tracked liver transaminases, creatine kinase, and non-cardiovascular deaths, including cancer.

What the trial found

Lipid changes

Simvastatin reduced total cholesterol by 25%, LDL cholesterol by 35%, and triglycerides by 10%, while raising HDL by 8%. The placebo group showed negligible change. These numbers held steady across the full follow-up period.

Primary endpoint: all-cause mortality

| Outcome | Simvastatin (n = 2,221) | Placebo (n = 2,223) | Relative risk (95% CI) | p-value | |---|---|---|---|---| | All-cause mortality | 182 (8.2%) | 256 (11.5%) | 0.70 (0.58, 0.85) | 0.0003 | | Coronary death | 111 (5.0%) | 189 (8.5%) | 0.58 (0.46, 0.73) | <0.00001 |

Over 5.4 years, 256 patients died in the placebo arm versus 182 in the simvastatin arm, an absolute risk reduction of 3.3 percentage points. The number needed to treat (NNT) to prevent one death was approximately 30 over that period. The Kaplan-Meier survival curves began separating around one year and continued to diverge throughout follow-up.

Secondary endpoints

| Outcome | Simvastatin | Placebo | Risk reduction | |---|---|---|---| | Major coronary events | 431 (19.4%) | 622 (28.0%) | 34% (p < 0.00001) | | Revascularization procedures | 252 | 383 | 37% (p < 0.00001) | | Non-fatal MI | 207 | 274 | Significant reduction | | Cerebrovascular events | 70 | 98 | 30% (p = 0.024) |

The reduction in revascularization procedures is clinically important for a practical reason: fewer bypass surgeries and angioplasties translate to reduced healthcare costs and patient burden. The reduction in stroke was not a pre-specified primary outcome, but it was one of the first signals that statins might protect beyond the coronary arteries.

Safety data

There was no increase in non-cardiovascular death, including cancer mortality (simvastatin: 35 vs. placebo: 33). This was reassuring because earlier cholesterol-lowering trials had raised worry about possible cancer links. Clinically significant elevations in liver enzymes (more than 3x the upper limit of normal) were rare and similar between groups. No cases of rhabdomyolysis were reported. The 4S safety data helped establish the tolerability profile that supported simvastatin's later FDA approval for coronary mortality reduction.

Limitations the investigators acknowledged

The trial population was narrow by design. Nearly all participants were white Scandinavians. Women made up only 19% of the cohort, and subgroup analysis in women did not reach statistical significance for the primary endpoint (though the direction of effect was consistent). Patients older than 70 were excluded entirely.

Baseline cholesterol levels were relatively high (mean LDL around 4.9 mmol/L, or 188 mg/dL). Whether the benefit would extend to patients with lower cholesterol was left unanswered until later trials like CARE and LIPID.

The trial also could not separate the drug effect from the LDL-lowering effect. It remained theoretically possible that simvastatin's survival benefit came from pleiotropic effects (anti-inflammatory, endothelial stabilization) rather than cholesterol reduction alone.

What changed because of 4S

The trial's impact on clinical practice was immediate and lasting. Before 4S, prescribing cholesterol-lowering drugs to prevent death was speculative. After 4S, it became evidence-based.

Within two years of publication, the American Heart Association and ACC revised lipid guidelines to recommend statin therapy for secondary prevention in CHD patients. Simvastatin (branded as Zocor by Merck) became one of the most prescribed drugs in the world. The trial gave the entire statin class clinical credibility that subsequent mega-trials (WOSCOPS, HPS, JUPITER) extended to primary prevention and broader populations.

The current 2018 ACC/AHA cholesterol guidelines classify patients with established atherosclerotic cardiovascular disease as the highest-priority group for high-intensity statin therapy, a recommendation whose foundation traces directly to the 4S result.

How to read the 30% number

A 30% relative risk reduction sounds large, and it is. But the absolute numbers add context. Out of 2,223 placebo patients, 256 died. Out of 2,221 simvastatin patients, 182 died. The absolute difference is 74 fewer deaths, or about 3.3 percentage points. For individual patients, the NNT of roughly 30 over 5.4 years means that for every 30 patients treated with simvastatin for that duration, one additional life was saved. The other 29 either would not have died anyway or died despite treatment.

This is not a criticism. An NNT of 30 for mortality prevention is strong by cardiovascular medicine standards. But it means the benefit is population-level. No individual patient can know whether they were the "one in thirty."

Where 4S sits in the statin evidence timeline

4S was the proof of concept. Subsequent trials expanded the evidence:

CARE (1996): showed benefit at lower cholesterol levels (mean LDL 150 mg/dL)
LIPID (1998): confirmed mortality reduction in a broader CHD population
HPS (2002): demonstrated benefit across wide cholesterol ranges and in diabetics
JUPITER (2008): extended statin use into primary prevention for patients with elevated CRP

Each trial answered a progressively wider question. 4S answered the narrowest and most important one first: do statins prevent death?

Frequently asked questions

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References

Scandinavian Simvastatin Survival Study Group. Randomised trial of cholesterol lowering in 4444 patients with coronary heart disease: the Scandinavian Simvastatin Survival Study (4S). The Lancet. 1994;344(8934):1383-1389. PubMed
Sacks FM, Pfeffer MA, Moye LA, et al. The effect of pravastatin on coronary events after myocardial infarction in patients with average cholesterol levels (CARE). N Engl J Med. 1996;335(14):1001-1009. PubMed
The Long-Term Intervention with Pravastatin in Ischaemic Disease (LIPID) Study Group. Prevention of cardiovascular events and death with pravastatin in patients with coronary heart disease and a broad range of initial cholesterol levels. N Engl J Med. 1998;339(19):1349-1357. PubMed
Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC Guideline on the Management of Blood Cholesterol. Circulation. 2019;139(25):e1082-e1143. PubMed
FDA. Zocor (simvastatin) prescribing information. FDA Label