GLP stands for Good Laboratory Practice, a set of regulations that govern how nonclinical safety studies are conducted before a drug, medical device, or other regulated product can be tested in humans. In the pharmaceutical industry, GLP ensures that the laboratory data submitted to regulatory agencies like the FDA is trustworthy, reproducible, and free from manipulation. It covers everything from how a lab is organized and staffed to how raw data is recorded, reviewed, and archived.
What GLP Actually Regulates
GLP applies specifically to nonclinical laboratory studies, meaning the safety testing that happens before clinical trials begin. These are the studies that evaluate whether a new drug candidate is toxic, how it behaves in the body, and what doses might be safe enough to try in people. Think of toxicology studies in animals, safety pharmacology assessments, and certain tests of how a compound is absorbed, distributed, and eliminated.
The scope is broader than just drugs. Under FDA regulations (21 CFR Part 58), GLP covers studies supporting applications for human and animal drugs, biological products, medical devices, food and color additives, and electronic products. The common thread is that any nonclinical safety data you submit to the FDA to get a research or marketing permit must come from a GLP-compliant study.
Early-stage discovery research, where scientists are screening compounds or exploring basic biology, does not need to follow GLP. The rules kick in once a study is specifically designed to generate safety data that will support a regulatory submission. This distinction matters because GLP compliance adds significant cost and overhead, so companies apply it selectively to the studies that require it.
Why GLP Exists
GLP regulations trace back to one of the largest scientific fraud scandals in U.S. history. In the 1970s, Industrial Bio-Test Laboratories (IBT) was the nation’s largest private testing lab, responsible for roughly 22,000 toxicology studies and handling an estimated 35% to 40% of all tests conducted in private labs across the country. Investigations revealed that IBT had fabricated and manipulated safety data on behalf of corporate clients, including chronic toxicity studies on chemicals like PCBs. The fraud ultimately led to criminal indictments and convictions of IBT employees.
The scandal exposed a fundamental problem: regulators had no standardized way to verify that the safety data companies submitted was actually generated through sound, honest science. The FDA finalized GLP regulations in 1978 to close that gap, creating enforceable standards for how labs must plan, conduct, monitor, and report nonclinical studies.
How a GLP Study Is Organized
Every GLP study revolves around two key roles. The Study Director is the single individual responsible for the overall conduct of the study. This person approves the study protocol, ensures the plan is followed, and signs off on the final report. There is always exactly one Study Director per study, creating a clear chain of accountability.
The Quality Assurance Unit (QAU) serves as an independent check on the Study Director and the lab. The QAU can be a person or a team, but it must be organizationally separate from the people running the study. Its job is to inspect the study at critical phases, audit the final report, and report findings directly to facility management. This separation prevents the people generating data from also being the ones verifying its integrity.
Beyond these roles, GLP requires that every facility maintain detailed Standard Operating Procedures (SOPs) covering all routine operations. SOPs exist so that every technician handling a sample, calibrating an instrument, or caring for test animals follows the same steps every time. The goal is to minimize systematic errors and make studies reproducible. During an FDA inspection, the SOP index is one of the first documents requested.
Equipment, Facilities, and Calibration
GLP-compliant labs must maintain and calibrate all equipment on a documented schedule. Calibration records, environmental monitoring logs, and instrument maintenance records are all considered raw data under the regulations, meaning they must be preserved with the same rigor as study results. The FDA’s position is straightforward: calibration should be frequent enough to assure data validity, and the schedule must be written into the facility’s SOPs. Even when an equipment manufacturer performs the maintenance, the facility must document that it happened according to defined procedures.
Data Integrity and Record Keeping
The documentation requirements under GLP are intentionally strict. Every observation, measurement, and calculation generated during a study qualifies as raw data and must be recorded promptly in ink, with any corrections made so the original entry remains visible. This creates an auditable trail from the moment data is generated through the final report.
Retention requirements vary by situation, but the general framework requires that raw data, specimens, and final reports be kept for whichever period is longest: the duration of the marketing permit the study supports, five years after the data is submitted to the agency, or two years after a study is completed or terminated if the data was never submitted. For a successful drug, this can mean decades of archival storage.
How the FDA Enforces GLP
The FDA conducts routine inspections of GLP facilities and classifies each inspection into one of three categories. A “No Action Indicated” (NAI) result means no problems were found. “Voluntary Action Indicated” (VAI) means the inspectors found objectionable conditions but the agency isn’t recommending formal enforcement action, essentially a warning to fix the issues. “Official Action Indicated” (OAI) is the most serious classification and means the FDA is recommending regulatory or administrative action, which can include warning letters, study rejections, or disqualification of the facility.
An OAI classification can derail a drug development program. If the FDA determines that a pivotal safety study was not conducted under proper GLP conditions, it can refuse to accept the data. That can mean repeating months or years of nonclinical work before clinical trials can proceed.
Where GLP Fits in the Drug Development Timeline
GLP is one of three major “GxP” frameworks that govern pharmaceutical development, and each one applies at a different stage. GLP covers the preclinical phase, before any human testing begins. Once a drug moves into clinical trials involving human volunteers, Good Clinical Practice (GCP) takes over. Good Manufacturing Practice (GMP) governs how the drug is physically produced and applies from manufacturing through the product’s entire commercial life.
These systems are sequential but sometimes overlap. A company might be running GLP-compliant toxicology studies for a new indication while already manufacturing the drug under GMP for an existing one. The important distinction is that GLP is specifically about the integrity of laboratory-generated safety data, not about manufacturing quality or clinical trial ethics. Each framework addresses a different type of risk in a different setting, but together they form the regulatory backbone that a drug must pass through on its way from the lab to the pharmacy shelf.