The Common Technical Document (CTD) is the agreed structure for a marketing application dossier. It sorts everything you file about a medicine into five modules: regional administrative material, high-level summaries, quality and manufacturing data, nonclinical study reports, and clinical study reports. It was developed under ICH M4E(R2) and the related M4 guidelines so that a company could organize much of one dossier and file more broadly across the US, the EU, and Japan, rather than assembling a wholly different one for each. Significant regional requirements still remain, especially in Module 1 and in certain region-specific content, so the harmonization is partial rather than complete.

That last point is easy to take for granted now. Before the CTD, every region wanted its own format. The same clinical and manufacturing data had to be repackaged into a US NDA structure, then a European structure, then a Japanese one, each with its own ordering and expectations. The science was identical; the paperwork was three separate jobs. ICH M4, finalized around 2000 and adopted by FDA, EMA, and Japan's PMDA, replaced that with a common outline. Module 1 stays regional, but Modules 2 through 5 are the same wherever you file.

If you write regulated documents, the CTD is the filing cabinet your work lands in. Knowing which drawer each document goes in, and which drawers you personally are responsible for, is part of the literacy of the job.

The triangle, described in words

Most people meet the CTD as a diagram: a triangle with a box sitting on top of it. The box on top is Module 1, drawn separately because it is region-specific and not technically part of the harmonized CTD at all.

The triangle itself is Modules 2 through 5. At the apex sits Module 2, the summaries. It is narrow because it is short: it distills everything below it. The wide base of the triangle is the detailed data, split into three columns that rise to meet the summaries: Module 3 (Quality), Module 4 (Nonclinical), and Module 5 (Clinical). The shape makes the logic visible. A reviewer can start at the top with the summaries and drill down into the full reports underneath whenever they want to check the source. Detail at the bottom, argument and distillation at the top.

Module 1: regional administrative information

Module 1 is everything specific to the region you are filing in. Application forms, cover letters, proposed labeling and prescribing information, patent and exclusivity statements, environmental assessments, risk-management plan documents, and other administrative pieces. Because a US form and an EU form are not interchangeable, this module was deliberately left outside the harmonized structure. FDA defines its Module 1 contents; EMA defines a different set. It is the one module you genuinely rebuild per region.

Module 2: the summaries, where regulatory writers live

Module 2 is where a lot of regulatory writing careers are spent, so it is worth slowing down on. It contains the connective tissue: a table of contents, an introduction, and then a set of overviews and summaries that sit above the detailed modules.

  • 2.3 Quality Overall Summary (QOS) — a summary of Module 3, the quality and manufacturing data.
  • 2.4 Nonclinical Overview — an interpretive assessment of the Module 4 data.
  • 2.5 Clinical Overview — an interpretive assessment of the Module 5 data.
  • 2.6 Nonclinical Written and Tabulated Summaries — detailed factual summaries of the nonclinical studies.
  • 2.7 Clinical Summary — a detailed factual summary of the clinical data.

The distinction that trips people up is between an overview and a summary, and it is not cosmetic. An overview argues. A summary summarizes.

The Clinical Overview (2.5) is short, often around thirty pages, and its job is to make the case: here is the development rationale, here is what the efficacy and safety data show, and here is why the benefits outweigh the risks. It is a critical, interpretive document. It reads like a well-reasoned argument because that is what it is meant to be, with subsections running from product development rationale through the benefit-risk conclusions.

The Clinical Summary (2.7) is longer and mostly factual. It walks through biopharmaceutics, clinical pharmacology, a summary of efficacy, a summary of safety, and synopses of the individual studies. It does not editorialize. It lays out what happened across the studies in an organized, comparable way so the reader can see the whole clinical program without opening every study report underneath.

2.5 and 2.7 are the two documents regulatory writers are most often handed, and understanding that one persuades while the other reports is the difference between a draft that lands and one that comes back covered in comments. The same split holds on the nonclinical side: 2.4 argues, 2.6 reports.

Module 3: quality and CMC

Module 3 holds the chemistry, manufacturing, and controls data, structured under the ICH M4Q guideline. At a high level it splits into the drug substance and the drug product, each covering things like the description and characterization, manufacturing process and controls, control of impurities, the specification and its justification, analytical methods and their validation, stability, and container-closure. Appendices and a regional section round it out.

Module 3 is a different animal from the narrative modules. It carries a great deal of interlocking tabular data alongside substantial narrative, and the same batch, impurity, or limit shows up in many places and has to read the same way everywhere. That property is much of what makes it hard to produce, and we've written about why that is a data problem, not a writing one. It is also why CMC / Module 3 authoring is a distinct discipline with its own authors, separate from the clinical writers upstairs in Module 2.

Module 4: nonclinical study reports

Module 4 contains the full nonclinical study reports, the primary-source documents that Module 2.4 and 2.6 summarize. Organized under ICH M4S, it covers pharmacology, pharmacokinetics, and toxicology: the animal and in-vitro work that supports first-in-human dosing and characterizes the safety profile before and alongside clinical development. These are the detailed reports; the interpretation of them lives up in Module 2.

Module 5: clinical study reports

Module 5 holds the clinical study reports, and in many applications it is among the more substantial modules, though its relative size varies by product and dossier. Its core is the set of individual Clinical Study Reports, each written to ICH E3, together with the listing of all clinical studies, reports of analyses of data from more than one study, and literature references. This is the evidentiary base of the whole submission. Everything in the Clinical Summary (2.7) and the Clinical Overview (2.5) traces down into these reports.

eCTD: the electronic packaging

The CTD is the content structure. The eCTD is how that content is packaged and transmitted electronically, and for most major markets electronic submission is now the required route.

Two ideas matter here. The first is granularity: the eCTD breaks the dossier into many individual files, each mapped to a place in the module structure, rather than a few enormous PDFs. The second is lifecycle. A submission is not a one-time drop; it evolves through review cycles and post-approval changes. The eCTD tracks each file with a lifecycle operation, so a later submission can specify that a document is new, or replaces an earlier version, or appends to it, or deletes it. These lifecycle operations help present the current view of a document while preserving the full submission history of what changed and when.

The current widely used standard is eCTD v3.2.2. A newer version, eCTD v4.0, exists and is built on a different technical foundation. Its adoption and implementation are jurisdiction-specific, and timelines and mandatory dates should be confirmed against each agency's current guidance rather than assumed.

Who writes what

The CTD is also a map of responsibilities, though the exact split varies from company to company. Regulatory writers usually lead the clinical narratives: the Clinical Overview (2.5), the Clinical Summary (2.7), and the CSRs in Module 5. CMC authors may typically lead Module 3 and its Quality Overall Summary in 2.3. Nonclinical writers or toxicologists usually lead Module 4 and the 2.4 and 2.6 summaries. Regulatory affairs and a publishing team may typically lead Module 1 and the eCTD backbone itself, the assembly, hyperlinking, validation, and submission.

The most common friction point sits right at the seam between 2.7 and Module 5. The Clinical Summary has to summarize the study reports beneath it, which means every number, every subgroup result, every safety count in 2.7 must agree with the CSR it came from. When a CSR is revised late, the summary can quietly drift out of sync, and reconciling the two is a real and recurring part of the work. Keeping a summary honest to the reports underneath it is a cross-referencing discipline, not a writing flourish.

If you want the fuller map of how these documents relate across a program, our complete guide to regulatory writing and the ICH guidelines every regulatory writer should know both build out from the structure sketched here. This is the page worth bookmarking when you need to remember which module a document belongs to, and why.