What are the three types of tests used on drugs? A guide to drug evaluation

October 11, 2025 •

4 min read

According to the Georgetown University Office of the Vice President for Research, over 90% of drug candidates fail during clinical trials, highlighting the rigorous testing process required for drug approval. A new medication must undergo three main types of tests used on drugs: preclinical studies, clinical trials, and ongoing toxicological monitoring after market release.

Quick Summary

The three primary types of tests for drugs are preclinical laboratory and animal studies, multi-phase human clinical trials, and post-market toxicology surveillance for ongoing safety monitoring.

Key Points

Preclinical Testing: Utilizes both computer models and living organisms (like lab animals) to evaluate a drug's potential effects and toxicity before it is introduced to humans.
Clinical Trials: A structured, multi-stage process involving human participants to test a drug's safety, dosage, efficacy, and compare it to existing treatments.
Post-Market Surveillance: An ongoing monitoring phase after a drug receives approval, which is crucial for identifying rare or long-term side effects that may not appear in controlled trials.
Initial Screening vs. Confirmation: In toxicology testing, an initial rapid immunoassay is often followed by a more precise test like gas chromatography-mass spectrometry (GC-MS) to confirm positive results.
High Failure Rate: The drug development process has a high rate of attrition, with over 90% of drug candidates failing during the clinical trial phases, often due to lack of efficacy or safety concerns.
Specimen Variety: Post-market drug testing can be performed on various biological samples, including urine, blood, hair, and saliva, each offering a different detection window.
The Purpose of Phases: Each phase of a clinical trial has a specific purpose, from Phase 1's focus on safety to Phase 3's goal of comparing the new treatment against the standard of care.

The path from a new chemical compound to an approved medication is long, complex, and highly regulated, designed to ensure patient safety and drug efficacy. This journey involves a series of progressively more rigorous evaluations, which can be broadly categorized into three main types of tests used on drugs: preclinical studies, clinical trials, and post-market surveillance.

Preclinical Testing: In the Lab and on Animals

Before a new drug can be tested on humans, it must first undergo extensive preclinical testing. This stage aims to determine if the drug is safe enough for human trials and if it shows potential therapeutic promise.

In Vitro Studies

These tests, conducted 'in glass' (e.g., in a petri dish or test tube), use computer models and isolated biological materials like human cells or tissues to evaluate a drug's initial effects and potential side effects. Many substances fail at this stage if they damage cells or fail to demonstrate a desired effect. Key in vitro methods include:

Cell-based assays: Measuring a drug's effect on living cells to assess toxicity and mechanism of action.
Biochemical assays: Testing a drug's interaction with specific biological molecules, like enzymes or receptors.

In Vivo Studies

Drug candidates that pass the initial in vitro screening are moved to animal testing, or 'in vivo' studies. These tests are mandated by regulatory bodies like the FDA to provide critical data on a drug's metabolism, efficacy, and toxicity in a living system before human exposure. Common animal models include mice and dogs.

Clinical Trials: Human Testing in Phases

If a drug is deemed safe in preclinical studies, it proceeds to human clinical trials. This phase is divided into four stages, each designed to answer specific questions about the drug's safety, efficacy, and optimal use.

Phase 1

Purpose: Primarily to test safety and find the right dosage.
Subjects: A small group (20-80) of healthy volunteers.
Goal: To identify side effects and understand how the drug is metabolized.

Phase 2

Purpose: To test efficacy in treating the target condition and further evaluate safety.
Subjects: A larger group (100-500) of patients with the illness.
Goal: To determine if the drug works as intended for the condition.

Phase 3

Purpose: To confirm efficacy and safety by comparing the new drug to standard treatments or a placebo.
Subjects: A large, diverse group (hundreds to thousands) of patients.
Goal: To prove that the new drug is better or safer than existing options.

Phase 4

Purpose: To monitor the drug's long-term safety and effectiveness after it has been approved and is available to the public.
Subjects: A diverse, extensive group of patients in real-world settings.
Goal: To gather additional data on side effects and long-term risks.

Post-Market Surveillance and Toxicology Testing

The final type of testing involves ongoing monitoring of a drug's effects after it is released to the market. This phase is crucial for detecting rare or long-term side effects that may not have been apparent in earlier trials.

Adverse Event Reporting

Regulatory agencies continuously collect and analyze reports from healthcare providers and patients regarding adverse events associated with a medication. This helps identify potential safety issues in the broader population.

Routine Drug Screening

As part of addiction treatment, employment screening, or forensic investigations, toxicological screens are performed on biological samples to detect drug metabolites. This typically involves a two-step process: an initial, rapid immunoassay followed by a more specific, confirmatory test like gas chromatography-mass spectrometry (GC-MS) for positive results.

Pharmacovigilance Studies

These large-scale observational studies track the safety and effectiveness of approved drugs over an extended period. Researchers analyze large databases to identify potential risks and benefits not seen in controlled clinical trial settings.

Comparison of the Three Types of Tests


Test Type	Purpose	Subjects	Detection/Duration
Preclinical	Determine a drug's safety, efficacy, and toxicity before human exposure.	Laboratory models (`in vitro`) and animals (`in vivo`).	Duration varies; ends before human trials begin.
Clinical Trials	Evaluate a drug's safety and efficacy in humans through controlled studies.	Healthy volunteers, then increasing numbers of patients.	Multi-phase process lasting several years.
Post-Market Surveillance	Monitor a drug's long-term safety and effectiveness in the general population.	Broad patient population and specific individuals being screened for drug use.	Ongoing, after regulatory approval; for drug screening, detection windows vary by substance and sample type (e.g., blood, urine, hair).

Conclusion

From initial laboratory analysis and animal studies to multi-phase human trials and continuous post-market monitoring, a new drug undergoes a series of crucial tests. The combination of these three types of tests used on drugs—preclinical, clinical, and surveillance—ensures that medications are thoroughly vetted for safety and efficacy. This systematic, multi-layered approach helps protect public health by minimizing risks and maximizing therapeutic benefits, even though it is an expensive and time-consuming process. The rigorous review process helps identify potentially life-saving treatments while filtering out those that are ineffective or too dangerous. For more information on drug safety and regulation, consult the U.S. Food and Drug Administration (FDA).

Frequently Asked Questions

During preclinical testing, a drug is evaluated using computer models, lab-grown cells, and animal models to assess its potential efficacy, toxicity, and safety before human trials are initiated.

An immunoassay is a faster, less expensive initial screening test that uses antibodies to detect drug classes, but can sometimes have false positives. A GC-MS test is a more specific and sensitive confirmatory test used to verify the presence and amount of a particular drug.

Drug candidates can fail during clinical trials for several reasons, including insufficient clinical efficacy (the drug doesn't work as hoped) or unacceptable toxicity (dangerous side effects).

Phase 4, or post-market surveillance, takes place after a drug is approved and monitors its long-term safety and effectiveness in a much larger, more diverse patient population.

Yes, some prescription or over-the-counter medications can cause false positive results on initial immunoassay drug screens due to chemical cross-reactivity. A confirmatory test is usually needed to resolve any discrepancies.

The drug development process is lengthy and costly, taking approximately 10 to 15 years and over a billion dollars to bring one new drug to market, largely due to high failure rates in testing.

Toxicology screens can use various biological samples, including urine (most common), blood, oral fluid (saliva), hair, and sweat, each with a different detection window.