Monday, 31 January 2022

Toxicology in forensic science


Forensic toxicologists perform scientific tests on bodily fluids and tissue samples to identify any drugs or chemicals present in the body. Working in a lab, the forensic toxicologist performs tests on samples collected by forensic pathologists during an autopsy or by crime scene investigators. They use highly sophisticated instruments, chemical reagents and precise methodologies to determine the presence or absence of specific substances in the sample.
As part of a team investigating a crime, a forensic toxicologist will isolate and identify any substances in the body that may have contributed to the crime, such as:

  • Alcohol

  • Illegal or prescription drugs

  • Other chemicals

  • Poisons

  • Metals

  • Gases, such as carbon monoxide

The work requires patience and the ability to follow specific steps to achieve reliable results. The forensic toxicologist must document every step of the process and take care to follow rules regarding chain of custody for physical evidence.

The field of forensic toxicology has grown to include drug and alcohol testing for employers and traffic enforcement officials as well as testing animal samples for wildlife criminal investigators and testing for “date rape” drugs and performance-enhancing substances.

Forensic toxicologists also work on cases involving environmental contamination, to determine the impact of chemical spills on nearby populations.

Investigators rely on the forensic toxicologist to make reliable conclusions about the impact a specific amount of a specific substance would have on a specific individual. Often, this requires the professional to form an educated opinion based on science and experience.

If asked to testify in court, the forensic toxicologist must be prepared to justify that opinion and to explain complex methodologies in terms a jury can understand.




Forensic Toxicology is study and practice of the application of toxicology i.e. scientific study of chemicals such as drugs, toxins and poisons; for the purposes of law and criminal investigation. It comprises but is not limited to identification and quantification of a particular drug, poison or substance in human tissue and interpretation of those results (DiMaio and Dimaio, 2001). Parcelsus who is considered Father of Toxicology defines that “Solely the dose determines that a thing is not a poison” meaning that anything can be harmful when taken in fatal amount. Some academicians also consider Matther Joseph Orfila as the Father of Modern Toxicology.

The primary aim is to find out whether a person died of poisoning or lethal overdose. Often it happens; a person is found to have fatal level of drug in their system but is not the cause of death. Tendency of this happening is because people have different tolerance level for a drug depending upon their absorption and metabolism (Dix and Calaluce, 1999). For instance, this might be the case with people who have build tolerance towards drugs for example habitual drug users. To accurately find correlation between drug and cause of death, it will depend upon various factors such as quality of a toxicology lab, scene investigation and autopsy findings (Dix and Calaluce, 1999). Another dangerous case which has become most prevalent in western countries, is Drug Facilitated Sexual Assault (DFSA). Perpetrators use date-rape drugs like Rohypnol, Liquid Ecstacy more commonly called Roofies, to trap women and assault them. The victims do not remember anything but toxicological screening can be used to find if there was the presence of above mentioned drugs in their system.

Drugs are introduced in body by several ways including but not limited to oral, intramuscular, intravenous, rectal, topical, subcutaneous and inhalation (Houck and Siegel, 2015). When a drug gets ingested and is distributed throughout the body the detection turns out to be a complex process. This is due to the fact that each drug has a different metabolic rate also depending how much quantity was ingested. In addition, certain drugs have preference for a particular organ or tissue. Nevertheless, the identification of any drug involves four main steps (Houck and Siegel, 2015).

        i.            Sampling

In all autopsy cases a minimum blood, urine, bile and vitreous are collected. Then again, every laboratory has its own SOP.

If human remains are in highly decomposed state and there are no viable tissues or organs or blood available to test for drugs, the toxicological analysis can be performed through maggots- a subfield of toxicology known as Entomotoxicology.  Studies have proved that insects are excellent evidence for drug analysis especially for drugs such as Barbiturates, Benzodiazepines, opiates and Cocaine (Dimaio and Dimaio, 2011).


      ii.            Extraction

This involves separation of drug from the biological sample. Techniques such as GC-MS, HPLC, TLC, Immunoassay or UV Spectrophotometry are used for the same.

a.       Liquid Phase Extraction

b.      Solid phase extraction

    iii.            Screening

Screening involves the preliminary testing of drugs in body fluids. Commonly, there are four general screens tests (Dimaio and Dimaio, 2011):

a.       First screen for Lower alcohols such as acetone, isopropyl alcohol, ethyl alcohol, n-propyl alcohol and methyl alcohol (Dimaio and Dimaio, 2011)

b.      Second screen for acidic and neutral screen such as barbiturates, salicylates, ethclorvynol and carbarnates. (Dimaio and Dimaio, 2011)

c.       Third screen is the basic screen for detection of tranquilizers, synthetic narcotics, local anaesthetics, antihistamines, antidepressants, and alkaloids. (Dimaio and Dimaio, 2011)

d.      Fourth screen is the narcotics careen for opiates, cocaine, methadone and other highly psychotropic substances (Dimaio and Dimaio, 2011)

    iv.            Confirmation

Once the preliminary tests detect presence of a drug, it has to be confirmed. The confirmatory method should be different and more sensitive than the preliminary testing method.

Analytical Techniques

Other than HPLC, GC-MS, UV Spectrophotometry which are used for detection of volatile substances; ICP-MS, AAS, AES can be used for detection, identification and sometimes quantification of inorganic compounds like Arsenic, Insecticides, Pesticides, Lead and such. 


Classification of drug/ poisons and their legal limit is unlikely to be uniform all over the globe as it changes from country to country. In India, based on mode of action poisons can be classified into six groups (Krishnamurthy, 2011):

1.      Corrosives- Strong acids such as Sulphuric acid HCl etc.

2.      Irritants- Inorganic, organic and mechanical substances such as phosphorus, castor oil, glass etc.

3.      Neurotics-  opium and other alkaloids, kerosene, malathion, insecticides etc

4.      Cardiac- digitalis, oleander etc

5.      Asphyxiants- Carbon monoxide, dioxide etc,

6.      Miscellaneous- antihistamine, tranquilisers etc.


Drugs and Cosmetics Act (1940)

This act defines the meaning of ‘drug’ and ‘cosmetic’ for the purposes of Legal proceedings as well as specifies manufacturing and how a particular drug will deem to be misbranded, adulterated or spurious.

With respect to Section 320 of Indian Penal Code (IPC), if a person is found to use adulterated, spurious or any other drug for diagnosis, treatment, mitigation or prevention of disease which causes ill health or bodily harm, shall be punishable for minimum of five years of imprisonment that may extend to term of life with a minimum fine of Rs. 10,000 (Vij, 2011).

The Drugs and Cosmetics Rules (1945)

A derivative of above act which covers all kind of drugs used in therapeutic ayurvedic, unani and siddha preparations.  These rule have classified drugs into various schedules.

Drugs and Magic Remedies (Objectionable advertisement) Act (1954)

This act ensures advertisements of drugs are up to ethical standards and can be banned if they promote offensive and immoral material. Magical remedies such as ‘Mantras’ and ‘Kavachas’ are also taken care of under this act (Vij, 2011).

Narcotic Drugs and Psychotropic Substances Act (1985)

India is a part of three United Nations drug convention; 1961 Convention, 1971 Convention and 1988 Convention (Tandon, 2015). Thereafter, the NDPS Act came into force. NDPS is an “act to consolidate and amend the law relating to narcotic drugs, to make stringent provisions for the control and regulation of operations relating to narcotic drugs and psychotropic substances” (NDPS Act, 1985). This act forbids cultivation, production, possession, sale, purchase, trade, import export, use and consumption of narcotic drugs and psychotropic substances except for medical and scientific purposes in accordance with the law (Tandon, 2015). The amendments of this act were taken thrice; in 1989, 2001 and 2014.

The death penalty is included in NDPS Act for repetitive production, manufacture, possession, transportation, import and export of drugs in large quantity (Tandon, 2015).

The Prevention of Illicit Traffic in Narcotic Drugs and Psychotropic Substances Act (1988)

The PITNDPS Act, 1988 aims “to provide for detention in certain cases for the purpose of preventing illicit traffic in narcotic drugs and psychotropic substances and for matters connected therewith”.

Legal Provisions Related To Toxicology In Accordance With Indian Legislation

Section 176 of IPC: Provides punishment for omission to give notice or information including that of a poisoning case) to the public servant/police.

Section 177 of IPC: Provides punishment for furnishing false information (including that of poisoning case).

Section 201 of IPC: Provides punishment for causing disappearance of evidence of offence (e.g., destroying sample of gastric lavage, clothing carrying evidence of poison etc.)

Section 202 of IPC: Provides punishment for intentional concealment of information of offense (including that of a poisoning case).

Section 269 of IPC: Negligent act likely to spread infection of disease dangerous to life.

Section 270 of IPC: Malignant act likely to spread infection of disease dangerous to life.

Section 271 of IPC: Disobedience to quarantine rule (‘quarantine’ means period of isolation imposed upon persons or animals that have arrived from elsewhere or been exposed to infectious or contagious disease).

Section 272 of IPC: Adulteration of food or drink intended for sale.

Section 273 of IPC: Sale of noxious food or drink.

Section 274 of IPC: Adulteration of drugs.

Section 275 of IPC: Sale of adulterated drugs.

Section 276 of IPC: Sale of drug as a different drug or preparation.

Section 277 of IPC: Fouling water of public spring or reservoir.

Section 278 of IPC: Making atmosphere noxious to health.

Section 284 of IPC: Prescribes for rash or negligent act (or omission) in relation with poisonous substance so as to endanger human life or to be likely to cause hurt or injury to any person.

Section 299 of IPC: Culpable homicide including that caused through administration of some poisonous substance.

Section 300 of IPC: Murder including that caused through administration of poisonous substance with the intention of causing death.

Section 304-A of IPC: Causing death by rash or negligent act (or omission) including that caused through poisoning.

Section 324 of IPC: Makes simple hurt more grave and liable to a more severe punishment—where it has been inflicted by one of the means described in the Section such as ‘fire’ or ‘any heated substance’, poison or any substance that is deleterious to the human body to inhale, swallow, or to receive into the blood.

Section 326 of IPC: It is similar to Section 324 with the only difference that the words ‘grievous hurt’ have been substituted for the word ‘hurt’ providing enhanced punishment.

Section 328 of IPC: Provides punishment for causing hurt by means of poison or any stupefying, intoxicating or unwholesome drug or other thing with the intent to commit an offence (i.e., anything when used in unwholesome state/composition can act as a poison).










Table 1. Punishment Table according to the quantity possessed (Tandon, 2015)


Small Quantity




Quantity greater than small but lesser than commercial (intermediate)



Maximum of 1 year rigorous imprisonment or a fine up to Rs. 10,000 or both


Rigorous imprisonment from 10 years (min) to 20 years (max) and a fine from Rs. 1L to Rs. 2L





Rigorous imprisonment that may extend to 10 years and fine that may extend to Ts. 1L




Ganja (Cannabis)



Charas (Cannabis Resin)




Coca Leaf

























Section 45 of the Indian Evidence Act, allows opinions of experts admissible. “The duty of an expert witness is to furnish the judge necessary scientific criteria for testing the accuracy of the conclusion so as to enable the judge to form his independent judgment by application of the criteria to the facts proved by the evidence.”. A toxicologist should specify all the necessary details such as what were the initial signs of poisoning, what preliminary and confirmatory tests were performed, and there results. However, it is not job of an expert to draw conclusion but to only list out the most probable manner of death.


A medico legal report (MLR) prepared by Doctors or Medical Examiner/ Coroner in cases of Toxicological cases, should comprise of following details:

         What drug was consumed by the victim?

         What was the method of ingestion?

         How much time before death was drug consumed by victim?

         Why did the victim consume that drug? (Intelligence report)

         What was the quantity of drug present in the system when analysed?

         What was the effect of drug on the victim’s body? (Was it fatal, or by-products were harmful?)

         How did victim got in possession with that drug? (Intelligence report)


Di Maio, D.J. & Di Maio, Vincent J. M 2001, Forensic pathology, 2nd edn, CRC Press, Boca Raton.

Dix, J., Calaluce, R. & Ernst, M.F. 1999;1998;, Guide to forensic pathology, CRC Press, Boca Raton

Houck, M.M. & Siegel, J.A. 2015, Fundamentals of forensic science, 3rd edn, Academic Press, Amsterdam.

Krishnamurthy, R. (2011) Forensic Science in Criminal Investigation, SSB, Delhi, India

NDPS Act 1985

Tandon, T. (2015) Drug Policy in India, International Drug Policy Consortium, London, UK.

Vij, K. (2011)Textbook of Forensic Medicine and Toxicology: Principles and Practice. 5th Edn. Chennai, India.

Website Referred—Law-of-Evidence.html


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