In Canada in 2013, Cannabis offences accounted for two-thirds of all police-reported drug offences with cannabis possession accounting for more than half of all drug offences.  The next most common type of police-reported drug offences in 2013 was cocaine-related (16% of all police-reported drug offences) as has been the case each year for more than two decades. Unlike cannabis and other illicit drugs where the majority of offences are related to possession, cocaine-related crime was more likely to involve supply offences (56% of all police-reported cocaine offences in 2013). Methamphetamines (4% of all police-reported drug offences), heroin (1%), ecstasy (less than 1%) and other banned substances (11%) made up the remainder of police-reported drug-related offences in 2013. - Statistics Canada website: www.statcan.ca

Defining Forensic Toxicology

Toxicology is the study of the origin, nature, and properties of various drugs, poisons, and toxins. Toxicological specialists work in hospitals where the identification of an overdose can mean life or death.

The terms drugs, poisons, and toxins have subtle and often overlapping definitions.

• Drugs are usually substances ingested intentionally to produce a change that results in better health, pain relief, or pleasure.
• Poisons are usually substances ingested unintentionally that cause poorer health. Most drugs can be taken at high doses to become poisons. One common method of attempting suicide is to take too many drugs or to ingest poison intentionally.
• Toxins are harmful environmental chemicals that cause negative health effects, usually after prolonged exposure. However, exposure to toxins at high concentrations can quickly cause harmful effects or even death. Intentionally exposing someone else to a toxin is a crime.

Forensic toxicology is the application of toxicology in the pursuit of solving criminal cases. It generally is concerned with the detection and identification of drugs, poisons, or toxins that cause adverse physiological effects. Law enforcement agencies and medical examiner's offices require the services of forensic toxicologists. The main responsibility of a forensic toxicologist is to detect and identify the presence of drugs, poisons, or toxins in body fluids, tissues, and organs.

The work of a forensic toxicologist is generally in three main categories:

1. Testing for alcohol in blood and/or urine samples
2. Detection of drugs, poisons, and toxins in body fluids, tissues, or organs
3. Identification and measurement of the specific type of drug, poison, or toxin found within a subject

How Drugs Affect the Human Body

Most illegal drugs are psychoactive drugs; that is, they alter a person’s perception or mood. Some psychoactive drugs are known as depressants because they reduce an individual’s sense of alertness by causing relaxation (e.g., marijuana). Other psychoactive drugs are known as stimulants because they intensify an individual’s sense of alertness to cause hyperactivity (e.g., cocaine).

Psychoactive drugs can be taken orally or through injection, but they may be absorbed through body membranes such as those located in the nose, lungs, rectum, or vagina. To influence the human body, any type of drug must be absorbed into the blood stream and be transported to the body region where it has an affect. Initially, a drug can be detected both in the region it targets and throughout the bloodstream.

Drugs that are taken orally go through a slightly different process. Any drug absorbed through the digestive tract into the bloodstream must first pass through the liver before it travels to the body region that it affects. As the drug passes through the liver, some of the drug is broken down into metabolites. The amount of drug that gets metabolized depends upon a number of factors including the polarity and stability of the drug, the rate of absorption of the drug and the form of the drug ingested (tablet, capsule, liquid, etc.). Rates of metabolism also differ from individual to individual as determined by genetics and other environmental factors. Almost always, the metabolites of the original drug will have a different effect on the body region it targets than the original form of the drug. Sometimes, metabolism renders a drug completely inactive and it passes harmlessly out of the body but in other cases, the metabolite might be just as active as the original drug although it may target a slightly different body region or use a different pathway to achieve its effect. It is also possible for the original drug to be ingested in an inactive form that must be metabolized by the liver before it becomes active and has any effect on the body region that it targets. The effects of orally ingested drugs usually have a delayed onset when compared to other methods of drug delivery because of the additional time required for the drug to pass through the digestive tract, be absorbed by the blood stream, and metabolized by the liver.

Pathway #1

drugs taken → digestive → blood → liver → body region → liver → kidneys → excreted
   orally              tract           stream                they affect            

  

Drugs that are injected or are absorbed through body membranes pass immediately into the blood stream and travel directly to the body region they affect. Then, as the blood continues to circulate through the body, the drugs will pass through the liver and begin to be metabolized.

Pathway #2

drugs injected
or absorbed through → blood stream → body region → liver → kidneys → excreted
body membranes                                    they affect

  

Once the drug travels to the region of the body that it affects, it may also be broken down by that organ or system. Every time the blood circulates through the body, more and more of the drug is broken down by the liver and is eventually transported to the kidneys and excreted into the urine. The overall length of time that it takes the body to completely metabolize a drug into an inactive metabolite determines how long an individual will experience an effect from that drug. Therefore, forensic toxicologists may look for a drug or the breakdown products of a drug in three areas:

• the blood
• the urine
• the target region

Metabolism of a drug happens over time. As a result, depending on which metabolite they are testing for, forensic toxicologists can detect the presence of a drug or one of its metabolites, hours, days, weeks and months after the drug was originally taken. Rohypnol, the date rape drug, can now be tested for in urine up to 8 days after the original dose was taken where as cocaine can be tested for in hair up to 3-6 months after it has been used.

Most psychoactive drugs target the cells of the central nervous system (CNS), which consists of the brain and the spinal cord. Psychoactive drugs tend to alter the activity between the cells of the CNS known as neurons. More specifically, psychoactive drugs change or mimic the actions of the neurotransmitters released by the neurons. When stimulated, neurotransmitters are released by a neuron, and they move from that neuron through a space (called the synapse) towards a receptor neuron. When neurotransmitters come into contact with the receptor neuron, responses are triggered. After a neurotransmitter has triggered a receptor neuron, it is broken down quickly so it no longer produces an effect. Examples of responses that may be triggered by receptor neurons within the CNS are muscle and heart contractions, increased or slowed heart rate, the sensation of pain, the interpretation of visual images, emotions, and sleep.