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The drug discovery process is the research stage in which scientists identify a biological target, find molecules that act on it, and refine one of them into a development candidate. It proceeds through target identification, target validation, assay development, hit identification, hit-to-lead, lead optimisation and candidate selection. Discovery produces a molecule; it does not produce a finished medicine.
Drug Discovery at a Glance
Each stage removes molecules that cannot meet the programme's scientific requirements, so that resources concentrate on a small number of viable options.
Each stage produces a specific type of evidence, and each decision to continue rests on that evidence rather than on expectation.
The process concludes with a nominated development candidate: one molecule considered suitable for further investigation.
A candidate must then demonstrate that it can be formulated, measured, stabilised and manufactured to a defined quality standard.
What Is the Drug Discovery Process?
The drug discovery process is the sequence of scientific work that takes a disease hypothesis and converts it into a single molecule worth developing further. It begins with the biology of a disease and ends with a nominated development candidate supported by pharmacological, chemical and early safety evidence.
The process is best understood as a series of decisions rather than a series of tasks. At each stage, a research team asks whether the accumulated evidence still justifies further investment. Most molecules do not survive these decisions, and stopping a programme early is a legitimate and valuable outcome.
This article provides a drug discovery process overview for pharmaceutical and biotechnology professionals: what happens at each stage, what evidence that stage produces, and which decision it supports. It also addresses a question that most published material omits, namely what a nominated candidate must still demonstrate before it can be developed into a medicine.
Understanding the drug discovery process matters commercially as well as scientifically. Programme decisions, partner selection, in-licensing assessments and development planning all depend on an accurate view of what discovery has established and what remains unresolved.
Drug Discovery and Drug Development: What Is the Difference?
Drug discovery identifies and optimises a molecule. Drug development turns that molecule into a medicine that can be manufactured, tested, administered and approved. Discovery answers whether a compound acts on the intended target; development answers whether it can become a controlled, reproducible product.
The two are frequently treated as a single activity, which causes practical problems. A compound with excellent target activity may prove impossible to formulate at a viable dose. A promising chemical series may have solid-state behaviour that undermines stability. These are development questions, and they are not resolved by discovery data.
The distinction also determines organisational responsibility. Discovery work is typically led by medicinal chemists, pharmacologists and biologists. Development work is led by formulation scientists, analytical chemists, regulatory professionals and manufacturing teams. The drug discovery development process depends on a deliberate, well-documented handover between the two.
A practical definition
If the question concerns which molecule to take forward, it belongs to discovery. If the question concerns how that molecule becomes a dosable, measurable, stable product, it belongs to development.
For a detailed treatment of the stages that follow discovery, see our guide to the pharmaceutical drug development process.
What Are the Stages of the Drug Discovery Process?
The drug discovery process has seven stages: target identification, target validation, assay development, hit identification, hit-to-lead, lead optimisation and candidate selection. Each stage produces defined evidence and supports a specific decision about whether the programme continues.
This drug discovery overview follows the sequence most commonly described in the scientific literature. Stage names and groupings vary between organisations: some programmes combine assay development with hit identification, and others treat candidate selection as part of preclinical planning.
Swipe horizontally to view the full table.
| Stage | Principal activity | Evidence produced | Decision supported |
|---|---|---|---|
| 1. Target identification | Link a disease mechanism to a specific protein, gene or pathway. | Biological rationale from genetic, clinical and literature evidence. | Is this target worth investigating? |
| 2. Target validation | Confirm that modulating the target affects the disease process. | Experimental confirmation in relevant cellular or animal systems. | Is the target likely to be therapeutically relevant? |
| 3. Assay development | Build a reliable, reproducible test of target activity. | A validated assay with acceptable reproducibility and signal quality. | Can activity be measured consistently enough to screen? |
| 4. Hit identification | Screen compound libraries to find molecules that act on the target. | Confirmed hits with measured activity and verified structure. | Are there tractable starting points? |
| 5. Hit-to-lead | Modify promising hits to improve potency and selectivity. | Structure-activity relationships across a chemical series. | Which series merits full optimisation? |
| 6. Lead optimisation | Refine the lead series across potency, selectivity, safety and drug-like properties. | An integrated profile covering pharmacology, metabolism and early safety. | Is any molecule good enough to nominate? |
| 7. Candidate selection | Nominate one molecule for development. | A consolidated evidence package supporting the nomination. | Does this molecule justify development investment? |
Target Identification
Target identification establishes why a molecular intervention might treat a disease. Researchers link a disease phenotype to a specific protein, gene or pathway whose modulation could produce therapeutic benefit. Evidence typically comes from human genetics, disease biology, clinical observation and published literature.
Two practical questions shape this stage. First, is the target likely to be involved in the disease rather than merely associated with it? Second, is the target accessible to the intended type of molecule? A target located in a compartment that small molecules cannot reach presents a different problem from one that is simply difficult to inhibit.
Target Validation
Target validation tests the hypothesis experimentally. The objective is to establish that modulating the target changes the disease process in a relevant biological system, using approaches such as genetic knockdown, knockout models, tool compounds or antibody reagents.
Validation is a matter of degree rather than a binary result. Confidence accumulates across independent methods and models. Programmes frequently advance on partially validated targets, in which case the residual uncertainty should be documented and revisited as further data emerge.
Assay Development
An assay is a laboratory test that measures whether a compound acts on the target. Before screening can begin, the assay must be shown to be reproducible, to distinguish active from inactive compounds reliably, and to remain stable across the plates and conditions used in large-scale testing.
Assay quality determines the quality of everything downstream. A poorly configured assay produces false positives that consume months of chemistry effort, and false negatives that discard viable starting points without record. Counter-screens and orthogonal assays are used to confirm that measured activity reflects genuine target engagement.
Hit Identification
Hit identification searches compound collections for molecules that show measurable activity against the target. High-throughput screening tests large libraries systematically; focused, fragment-based and knowledge-based approaches test smaller, more deliberately selected sets.
An initial screening result is a starting point, not a finding. Apparent actives must be confirmed by retesting, by verifying compound identity and purity, and by excluding common artefacts such as aggregation or assay interference. The confirmed hits that remain are then grouped into chemical series for further work.
Hit-to-Lead
In the hit-to-lead stage, medicinal chemists make systematic structural modifications to confirmed hits and measure the effect of each change. The resulting structure-activity relationships indicate which parts of the molecule drive activity and which can be altered.
Selectivity becomes important at this point, since a compound that acts on unintended targets carries a higher risk of adverse effects. Synthetic accessibility also matters: a series that cannot be made efficiently will constrain every subsequent stage. Programmes commonly advance more than one series to reduce the risk of a late failure.
Lead Optimisation
Lead optimisation refines the selected series against several requirements at once. Potency and selectivity must be maintained or improved while absorption, distribution, metabolism, excretion and toxicity (ADMET) properties are brought into an acceptable range.
These requirements frequently conflict. A modification that improves potency may reduce solubility; one that improves metabolic stability may introduce a safety signal. Lead optimisation is therefore an exercise in balancing competing properties rather than maximising any single one. This stage typically consumes the largest share of discovery time and chemistry resource.
Candidate Selection
Candidate selection nominates one molecule to enter development. The decision draws on the full evidence package: pharmacology, selectivity, ADMET profile, early safety findings, intellectual property position, projected human dose and the practicality of supplying material.
Nomination is a programme decision made by people, not a result produced by an experiment. It records that the available evidence justifies development expenditure. It does not establish that the molecule will succeed, and it does not confirm that the molecule can be formulated into a viable product.
Drug Discovery Methods and Approaches
Drug discovery methods fall into two broad groups. Target-based approaches start from a defined molecular target and search for compounds that act on it. Phenotypic approaches start from an observable biological effect and identify the mechanism afterwards.
The choice of drug discovery method depends on how well the disease biology is understood, what assays are available and what chemical starting points exist. Most organisations use several approaches across a portfolio rather than committing to one.
Further approaches address different starting points. Fragment-based discovery screens very small molecules that bind weakly, then grows or links them into larger compounds. Natural-product discovery examines compounds produced by plants, microorganisms and marine organisms. Drug repurposing investigates whether an approved medicine has activity in another disease, which can shorten the path to clinical investigation because safety data already exist.
Pharmacological approaches to drug discovery
A pharmacological approach to drug discovery concentrates on how a compound behaves in a biological system rather than on its chemical structure alone. It examines the relationship between concentration and effect, the duration of that effect, selectivity across related targets, and behaviour in relevant disease models. These pharmacological approaches to drug discovery determine whether measured potency translates into a plausible therapeutic effect at an achievable exposure.
Computational methods now support most of these approaches. Virtual screening, molecular docking and property prediction help prioritise which compounds to synthesise and test. Generative models can propose new structures for evaluation. These outputs guide experimental work rather than replace it; our article on the role of generative AI in drug discovery examines what this evidence currently supports.
After Candidate Selection: What a Molecule Must Still Prove
A nominated candidate has demonstrated that it acts on its target with acceptable selectivity and properties. It has not yet demonstrated that it can be made into a medicine. Before development can proceed with confidence, the molecule must be characterised as a physical substance and shown to be formulable, measurable and stable.
This is the least documented part of the new drug discovery process, and it is where a significant proportion of programmes encounter unexpected difficulty. A molecule that performed well in discovery assays may have poor aqueous solubility, an unstable crystalline form, incompatibility with common excipients, or degradation behaviour that only becomes apparent under stress conditions.
The work that answers these questions is early development, not discovery, and it has a distinct scientific character. Discovery measures what a molecule does. Early development measures what a molecule is: how it behaves as a solid, how it dissolves, how it degrades, and how reliably it can be measured.
Developability assessment
A developability assessment evaluates whether a candidate can realistically become a product. It reviews physicochemical properties, projected dose, likely dosage form, anticipated manufacturing route and the analytical work required. The purpose is to identify constraints while there is still an opportunity to address them, either by selecting a different salt or form, or by returning to a back-up molecule from the same series.
Conducting this assessment before nomination, rather than after, materially changes its value. A molecule selected partly on developability criteria carries less downstream risk than one selected on pharmacology alone.
Preformulation and physicochemical characterisation
Preformulation studies establish the fundamental properties that govern how a molecule can be formulated. This work is systematic rather than exploratory, and typically covers:
- Solubility and pH-solubility profiling: how much of the compound dissolves, in which media, and how that changes across the physiological pH range.
- Salt and polymorph screening: identifying the crystalline forms a molecule can adopt, selecting the form with the most suitable stability and solubility, and confirming that it does not convert to another form during processing or storage.
- Excipient compatibility: testing the molecule against candidate excipients to identify interactions that would cause degradation in a finished dosage form.
- Hygroscopicity and solid-state behaviour: how the material responds to moisture, temperature and mechanical stress during handling and manufacture.
- Forced degradation: deliberately stressing the molecule to identify its degradation pathways and the products that result.
These studies also generate the information needed to design a stability programme aligned with ICH quality guidelines, and they inform the target product profile that guides subsequent development.
Early analytical method development
Every claim made about a candidate depends on the ability to measure it. Early analytical method development establishes fit-for-purpose procedures for assay, related substances, dissolution and impurity profiling, so that results generated across studies and sites remain comparable.
Analytical work is frequently underestimated at this point in a programme. A method that cannot separate a degradation product from the active substance will not detect a stability problem. A dissolution method that does not discriminate between formulations cannot support formulation selection. Methods developed early, and developed properly, prevent data from having to be regenerated later.
Where Molkem Labs works
Molkem Labs operates at this interface between discovery and development. Its scope covers developability assessment, preformulation and physicochemical characterisation, solubility and pH-solubility profiling, salt and polymorph screening, excipient compatibility studies, and early analytical method development for new molecules — the work that establishes whether a discovery candidate can become a product.
From that foundation, the programme continues into formulation development, analytical and microbiological services, stability studies, technology transfer and regulatory support. The relevant scope for any individual project depends on the molecule, the intended dosage form and the markets concerned.
How Discovery Stages Differ From Phase I to Phase IV
The stages of drug discovery are not clinical trial phases. Discovery stages describe laboratory research conducted before any human exposure. Phase I to Phase IV describe clinical studies conducted in people, after regulatory permission has been granted.
The two sequences are frequently confused because both are described as "phases". They are separated by preclinical development, during which nonclinical safety studies, manufacturing development and the regulatory submission are completed. Only after an authority permits a clinical trial can Phase I begin.
Swipe horizontally to view the full table.
| Period | What happens | Subjects |
|---|---|---|
| Drug discovery | Target identification through to candidate selection. | Laboratory systems and animal models. |
| Preclinical development | Nonclinical safety studies, formulation and analytical development, manufacture of clinical supplies, regulatory submission. | Laboratory systems and animal models. |
| Phase I–IV | Clinical investigation of safety, dose, efficacy and long-term performance. | Human participants, under approved protocols. |
The regulatory requirements for each step vary by product type, development pathway, market and current authority guidance. The US Food and Drug Administration (FDA) publishes one widely referenced description of the drug development process. Requirements should always be confirmed against current guidance for the specific product and jurisdiction.
The Drug Discovery Process in India
In India, the scientific stages of drug discovery are the same as elsewhere. What differs is the regulatory framework that applies once a molecule moves towards human study, which is set principally by the Central Drugs Standard Control Organisation (CDSCO) under the New Drugs and Clinical Trials Rules, 2019.
The pharmaceutical drug discovery process in India has expanded well beyond generic development. Indian companies and research institutions now run programmes on new chemical entities, and academic and industrial collaboration in early research has increased. Discovery research is not itself the subject of a permission under these Rules; obligations arise at the point where a sponsor seeks permission to conduct clinical trials or to import or manufacture a new drug. Other requirements can still apply to the work - to controlled substances, to imported materials, or to the use of animals - and should be confirmed for the specific programme.
The regulatory framework
The New Drugs and Clinical Trials Rules, 2019, made under the Drugs and Cosmetics Act, 1940, consolidated the requirements previously distributed across earlier rules. They govern clinical trial permissions, new drug approval, ethics committee registration, and bioavailability and bioequivalence studies.
Applications are submitted through CDSCO's online portal. Technical review may be referred to a Subject Expert Committee for specialised input, particularly for new chemical entities, before the Drugs Controller General of India issues a decision. Ethics committee approval is required in parallel for the proposed clinical study.
Practical implications for Indian programmes
- Nonclinical data packages should be designed from the outset against the requirements of every market the sponsor intends to enter, not India alone.
- Chemistry, manufacturing and controls work should progress alongside discovery, since a clinical trial application requires defined quality data.
- Responsibilities between the sponsor and its contract research and development partners should be documented before work begins.
- Requirements can change. Current CDSCO guidance should be confirmed for the specific product and proposed activity rather than assumed from previous programmes.
Our guide to regulatory affairs in drug development examines how these obligations are planned and managed across a programme.
Conclusion
The drug discovery process is a structured sequence of decisions that reduces a broad biological hypothesis to one molecule supported by evidence. Its seven stages each answer a specific question, and the value of the process lies as much in the programmes it stops as in the candidates it produces.
What discovery delivers, however, is a molecule rather than a medicine. The transition from candidate to product depends on a different body of evidence: how the substance behaves physically, whether it can be formulated and measured reliably, and whether its quality can be controlled consistently. Programmes that plan for that transition during discovery, rather than after it, carry less risk into development.
Frequently Asked Questions
What is the drug discovery process?
The drug discovery process is the research stage in which scientists identify a biological target, find molecules that act on it, and refine one of them into a development candidate. It runs from target identification through target validation, assay development, hit identification, hit-to-lead and lead optimisation to candidate selection.
What are the stages of the drug discovery process?
There are seven commonly described stages: target identification, target validation, assay development, hit identification, hit-to-lead, lead optimisation and candidate selection. Some organisations combine or rename these, but the underlying sequence is consistent: establish a target, find active molecules, improve them, and select one.
What is the difference between drug discovery and drug development?
Discovery identifies and optimises a molecule. Development turns that molecule into a medicine that can be manufactured, tested and approved. Discovery establishes that a compound acts on its target; development establishes that it can be formulated, measured, stabilised and produced to a defined quality standard.
How long does the drug discovery process take?
It varies considerably by target class, therapeutic area and the quality of the available starting points. Discovery is generally measured in years rather than months, with lead optimisation usually the longest stage. Published timelines should be treated as broad indications, since they depend heavily on the assumptions behind them.
What is target identification and validation?
Target identification links a disease to a specific protein, gene or pathway that a medicine might act on. Target validation then tests that hypothesis experimentally, using methods such as genetic knockdown or tool compounds, to establish whether modulating the target actually affects the disease process.
What is hit-to-lead in drug discovery?
Hit-to-lead is the stage at which confirmed screening hits are chemically modified to improve potency and selectivity while retaining drug-like properties. The resulting structure-activity relationships show which parts of the molecule matter, and the stage ends by selecting the chemical series worth optimising fully.
What is lead optimisation?
Lead optimisation refines a lead series against several requirements simultaneously: potency, selectivity, absorption, metabolism, excretion and early safety. These properties often conflict, so the work involves balancing them rather than maximising any one. It is usually the most resource-intensive stage of discovery.
What happens after a drug candidate is selected?
The candidate enters early development. Before larger investment, it should be characterised as a physical substance through developability assessment, preformulation, solubility and pH-solubility profiling, salt and polymorph screening, excipient compatibility and early analytical method development. Nonclinical safety studies and manufacturing development then follow.
What makes drug discovery successful?
Successful drug discovery generally depends on a well-validated target, reliable assays, tractable chemical starting points and honest decision-making at each stage. Programmes are also more likely to succeed when developability is considered during optimisation rather than after nomination, since formulation and stability constraints are far harder to resolve later.
Does Molkem Labs support discovery-stage molecules?
Molkem Labs works at the interface between discovery and development. Its confirmed scope covers developability assessment, preformulation and physicochemical characterisation, salt and polymorph screening, excipient compatibility and early analytical method development, alongside formulation, stability, regulatory and technology-transfer support. The applicable scope is defined for each product and project.
Moving a Candidate Into Development
Molkem Labs supports developability, preformulation, analytical, formulation, stability, regulatory and technology-transfer activities within a defined development programme. Enquiries are assessed against the product requirements and confirmed project scope.
