Forensic Drug Analysis: Purpose & Process

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  • 0:03 The Purpose of Drug Analysis
  • 0:35 Collection
  • 1:36 Preservation
  • 2:47 Analysis
  • 5:49 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson provides an overview of the way that drugs are collected, preserved, and analyzed in criminal investigations. You'll also learn the why, what, and how of drug analysis.

The Purpose of Drug Analysis

The ultimate purpose of forensic drug collection, preservation, and analysis is to ensure such evidence is legally admissible as evidence in a court of law. That's why it's an investigator's job to ensure the integrity of the drug evidence they have collected, from the time they laid their hands on it until the time it is presented as evidence in court. In this lesson, we'l explore some of the fundamental ways investigators collect, preserve, and analyze drug evidence.


Drugs must be accurately weighed during the collection process. This means weighing everything that is collected, including the drugs and the packaging material, and recording the weights. The exception to this rule is drugs that are in liquid form. These drugs are not weighed; instead, they're measured in liters, milliliters, or another metric unit that represents volume.

If the drugs are found in individual dosage forms, such as pills or tablets, or if they are individually packaged in packets, each dosage must be counted. In scenarios where there are so many identical units of a drug (for example, pills) that weighing each individual unit is not effective time-wise, investigators may choose to weigh 100 units of the drug and then divide that weight by 100 to estimate the weight of an average unit. Then, all of the units can be weighed together, and their weight can be divided by the individual unit's weight to estimate the total number of units.


Once collected, evidence must be stored in a way that preserves it. The drug and the packaging material is placed in the appropriate storage container. Some items are placed in sealed envelopes, while others are placed in airtight and watertight plastic containers.

Liquids can be kept in their original containers, assuming they have a tight seal, or they can be placed into an appropriate container, like a conical tube, and sealed in order to minimize evaporation. Some materials cannot be stored in plastic containers, for they may chemically interact with the plastic. In this case, they may need to be stored in glass containers whose lids are lined with non-reactive materials.

Some other general rules for preserving drug evidence include the following:

  • Living plants should be stored in non-airtight containers, such as bags. Airtight containers kill living plants.

  • Drug paraphernalia made from glass or other potentially sharp objects should be stored in solid containers only.

  • Lab equipment used to manufacture drugs should be placed in shock-proof containers.


During the analysis process, let's take a look at the questions forensic scientists consider: why, what, and how.


After the drugs have been properly collected and preserved, they must be analyzed. Why do we analyze the drugs? The obvious answer is to make sure they can be presented as evidence in a court of law. But more specifically, we analyze drugs to determine the following:

  • Qualitative analysis, to determine the identity of the actual substance. Is it cocaine?

  • Quantitative analysis, to determine the amount of a substance in a sample. A gram? A pound? A liter?

  • The concentration of a substance in a sample (also part of quantitative analysis).

  • The presence of contaminants or multiple drugs in one sample.

  • If the substance is a controlled substance, one that is illegal or prescription-only, or a poison.

  • If a sample of bodily fluids or tissues contains a concentration of a chemical that is in a therapeutic/safe range, or not. By 'or not', this could mean someone was poisoned or someone disobeyed the law when they had too much to drink.

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