Forensic Toxicology Practice Questions

Q: Which of the following central nervous system depressants is most commonly used for suicidal purposes?

Opium. **Explanation:** **1. Why Opium is the Correct Answer:** Opium and its derivatives (opiates) are potent **Central Nervous System (CNS) depressants**. In the context of forensic toxicology in India, opium remains one of the most commonly used substances for suicide due to its easy availability (especially in rural areas), high toxicity in overdose, and the painless nature of death it induces. It causes death primarily through **respiratory depression** by acting on the mu-receptors in the brainstem. **2. Why the Other Options are Incorrect:** * **Cocaine (Option B):** Cocaine is a potent **CNS stimulant**, not a depressant. It is more commonly associated with accidental overdose or recreational toxicity rather than planned suicidal attempts. * **LSD (Option C):** Lysergic acid diethylamide is a **hallucinogen (psychotomimetic)**. While it can cause severe "bad trips" or psychotic episodes, it has a very high safety margin regarding physical lethality and is rarely used as a primary means of suicide. * **Cannabis (Option D):** Cannabis acts as a **hallucinogen/depressant** depending on the dose, but it is considered to have exceptionally low toxicity. Fatal overdose from cannabis alone is virtually unknown, making it ineffective for suicidal purposes. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Triad of Opioid Poisoning:** Pinpoint pupils (miosis), respiratory depression, and coma. * **Exception to Miosis:** Pethidine (Meperidine) and Morphine (in terminal stages/asphyxia) may cause mydriasis. * **Antidote:** **Naloxone** is the specific competitive antagonist. * **Post-mortem finding:** "Froth at the mouth and nostrils" and "Oedema of the lungs" are characteristic findings in opioid deaths. * **Legal Status:** Opium is regulated under the **NDPS Act (1985)**.

Q: Which condition affects the anterior horn cells?

Strychnine poisoning. ### Explanation **Strychnine poisoning** (derived from *Strychnos nux-vomica*) is the correct answer because its primary mechanism of action involves the **spinal cord**. Strychnine acts as a potent, competitive antagonist of **glycine**, which is the main inhibitory neurotransmitter at the **anterior horn cells** of the spinal cord. By blocking glycine, it removes post-synaptic inhibition, leading to unchecked sensory stimulation and powerful, symmetrical muscle spasms (convulsions). **Analysis of Options:** * **Strychnine (Correct):** It specifically targets the Renshaw cell-mediated inhibition at the anterior horn, leading to "spinal convulsions." * **Dhatura poisoning:** This is a deliriant poison that acts centrally and peripherally as an **anti-cholinergic** agent (blocking muscarinic receptors). It does not affect the anterior horn cells; its classic symptoms include dilated pupils, dry mouth, and "muttering delirium." * **Botulism:** This is caused by *Clostridium botulinum* toxin, which acts at the **neuromuscular junction (NMJ)**. It prevents the release of acetylcholine from the pre-synaptic nerve terminal, leading to flaccid paralysis, not spinal cord irritation. **High-Yield Clinical Pearls for NEET-PG:** * **Opisthotonus:** The characteristic backward arching of the back seen in Strychnine poisoning due to the dominance of powerful extensor muscles. * **Risus Sardonicus:** A fixed, grinning expression caused by spasms of the facial muscles (also seen in Tetanus). * **Differential Diagnosis:** Strychnine poisoning mimics **Tetanus**. However, in Strychnine, the onset is sudden, and muscles relax completely between convulsions, whereas in Tetanus, muscle rigidity is persistent. * **Post-mortem finding:** Rigor mortis appears and disappears very early due to the exhaustion of ATP from severe convulsions.

Q: Black tongue and black teeth are seen in abuse of which substance?

Cocaine. **Explanation:** The correct answer is **Cocaine**. The characteristic finding of a **"black tongue"** (melanoglossia) and **"black teeth"** in cocaine abusers is primarily attributed to the method of consumption. When cocaine is smoked (especially in the form of "crack"), the smoke contains carbonaceous particles and impurities that deposit on the dorsal surface of the tongue and the dental enamel. Additionally, cocaine is a potent vasoconstrictor; chronic use leads to decreased salivary flow (xerostomia) and localized tissue ischemia, which promotes the accumulation of dark debris and predisposes the user to rapid dental decay and staining. **Analysis of Incorrect Options:** * **Cannabis:** Chronic use typically presents with "red eyes" (conjunctival injection) and dry mouth, but it does not cause specific black pigmentation of the tongue or teeth. * **LSD (Lysergic Acid Diethylamide):** As a hallucinogen, its physical signs are mainly sympathomimetic (mydriasis, tachycardia). It has no direct staining effect on the oral cavity. * **Heroin:** Opioid abuse typically presents with "pinpoint pupils" (miosis). While poor oral hygiene is common in addicts, the specific "black tongue" sign is not a diagnostic feature of heroin. **High-Yield Clinical Pearls for NEET-PG:** * **Magnan’s Symptom:** A tactile hallucination where the patient feels as if insects are crawling under the skin (formication); pathognomonic for cocaine. * **Cocaine Snorting:** Can lead to **perforation of the nasal septum** due to chronic ischemic necrosis. * **Body Packers/Stuffers:** Individuals who swallow packets of cocaine for smuggling; rupture can lead to fatal toxicity. * **Adulterants:** Cocaine is often cut with **Levamisole**, which can cause skin necrosis and agranulocytosis.

Q: Which poison resembles a viper snake bite?

Abrin. **Explanation:** **Abrin** is the correct answer because it is the toxalbumin derived from the seeds of *Abrus precatorius* (Jequirity or Ratti seeds). When these seeds are crushed and injected into the skin (often via "Sui" or needles used for cattle poisoning), the clinical presentation mimics a **Viperine snake bite**. Both conditions present with intense local inflammation, painful edema, ecchymosis, and necrosis at the site of injury. Systemically, both can lead to high fever, prostration, and fatal collapse. **Analysis of Incorrect Options:** * **Ricin:** Derived from *Ricinus communis* (Castor seeds). While it is a potent toxalbumin like abrin, its primary clinical feature is severe gastrointestinal irritation (hemorrhagic gastroenteritis) if ingested, or multi-organ failure if injected, but it does not classically mimic the local features of a viper bite. * **Crotin:** Derived from *Croton tiglium*. It is a powerful purgative and skin irritant causing vesication, but it is not the standard answer for mimicking viper envenomation. * **Bhilawanol (Bhi):** Derived from *Semecarpus anacardium* (Marking nut). It acts as a contact irritant causing blisters containing acrid serum, often used to simulate bruises in fabricated injuries, but does not resemble a snake bite. **High-Yield Clinical Pearls for NEET-PG:** * **The "Sui" Technique:** Small needles (Sui) are prepared by mixing Abrus powder with water/opium and are used for cattle poisoning or homicidal purposes. * **Diagnostic Clue:** To differentiate Abrin poisoning from a Viper bite, look for the presence of **fang marks**. Fang marks are present in snake bites but absent in Abrin poisoning (where a small puncture or the "Sui" itself may be found). * **Mechanism:** Abrin inhibits protein synthesis by inactivating the 60S ribosomal subunit (Type II Ribosome-Inactivating Protein).

Q: Which of the following poisons can be detected even from burnt bones?

Arsenic. **Explanation:** The correct answer is **Arsenic**. **1. Why Arsenic is correct:** Arsenic is a heavy metal known for its extreme stability and affinity for keratinized tissues (hair, nails) and bone. Unlike organic poisons, arsenic is an **inorganic element** that does not decompose or vaporize easily. It is often referred to as the "immortal poison" because it resists putrefaction, cremation, and the passage of time. Even after the body is burnt or buried for years, arsenic remains deposited in the bone matrix, making it detectable via chemical analysis (e.g., Marsh test or Reinsch test). **2. Why the other options are incorrect:** * **OPC (Organophosphorus Compounds):** These are organic chemical compounds that are highly volatile and degrade rapidly during putrefaction or exposure to heat. They would be destroyed instantly during cremation. * **LSD (Lysergic Acid Diethylamide):** This is a potent, heat-sensitive organic alkaloid. It is metabolized quickly in the body and destroyed by high temperatures. * **Cyanide:** Cyanide is a highly volatile gas/salt that acts rapidly and dissipates quickly. It is not stored in bone and would be lost during the burning process. **3. High-Yield Clinical Pearls for NEET-PG:** * **Arsenic & Exhumation:** Arsenic retards putrefaction (mummification-like effect), which is why it is often detected in exhumed bodies. * **Specimen of Choice:** In a living person, hair and nails are best for chronic poisoning. In a skeletonized or burnt body, **compact bone (femur)** is the specimen of choice. * **Other "Immortal" Substances:** Besides Arsenic, other heavy metals like **Antimony** and **Lead** can also be detected in bones after death. * **Aldrich-Mees Lines:** White transverse bands on nails seen in arsenic poisoning.

Q: Which of the following substances is NOT cardiotoxic?

Opium. **Explanation:** In forensic toxicology, poisons are classified based on their primary site of action. **Opium** is the correct answer because it is classified as a **Somniferous (Cerebral) Poison**, not a cardiotoxin. Its primary mechanism involves acting on opioid receptors in the Central Nervous System (CNS), leading to CNS depression, pinpoint pupils, and respiratory depression. While severe overdose can lead to secondary cardiac arrest due to hypoxia, its direct toxic effect is not on the myocardium or cardiac conduction system. **Analysis of Incorrect Options:** * **Aconite (Aconitum napellus):** Known as "Blue Rocket" or "Sweet Poison," it is a potent **cardiotoxin**. It contains aconitine, which opens voltage-gated sodium channels, leading to arrhythmias (typically bidirectional ventricular tachycardia) and cardiac arrest in diastole. * **Oleander (Nerium oleander/Cerbera thevetia):** These contain cardiac glycosides (like oleandrin and thevetin) which act similarly to Digoxin. They inhibit the Na+/K+-ATPase pump, causing profound bradycardia and heart block. * **Nicotine:** Found in tobacco, it acts on nicotinic acetylcholine receptors. In toxic doses, it causes initial stimulation followed by blockage of autonomic ganglia, leading to hypertension, tachycardia, and potentially fatal arrhythmias. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiotoxic Trio:** Aconite, Oleander, and Digitalis are the most frequently tested cardiac poisons. * **Aconite Key Sign:** "Tingling and numbness" of the tongue and mouth is a pathognomonic early sign of aconite poisoning. * **Opium Triad:** Coma, Pinpoint pupil, and Depressed respiration (RR < 12/min). * **Antidote:** Naloxone is the specific antidote for Opium/Opioids, whereas Digoxin-specific Fab fragments can be used for Oleander poisoning.

Q: What is the lethal dose of krait venom?

6 mg. **Explanation:** The Common Krait (*Bungarus caeruleus*) is one of the "Big Four" venomous snakes in India. Its venom is primarily **neurotoxic**, containing potent pre-synaptic and post-synaptic toxins that lead to muscular paralysis and respiratory failure. * **Why 6 mg is correct:** The lethal dose of Krait venom for an average adult is approximately **6 mg**. Despite being less aggressive than the Cobra, the Krait's venom is significantly more potent; it is considered the most toxic among the Indian terrestrial snakes. For comparison, the lethal dose of Cobra venom is much higher (12–15 mg). * **Why other options are incorrect:** * **3 mg:** This is too low for a lethal dose in humans, though it represents the high potency of the venom. * **12 mg:** This is closer to the lethal dose of **Cobra venom** (approx. 12–15 mg). * **15 mg:** This represents the upper limit of the lethal dose for **Cobra venom** or the lethal dose for **Russell’s Viper** (approx. 15 mg). **Clinical Pearls for NEET-PG:** 1. **Nature of Venom:** Krait venom is **neurotoxic**. Unlike Cobra bites, Krait bites are often **painless** with minimal local swelling, frequently occurring at night while the victim is asleep. 2. **Early Morning Neuroparalysis:** A classic presentation where the patient wakes up with ptosis, diplopia, or respiratory distress. 3. **Management:** Treatment involves polyvalent Anti-Snake Venom (ASV). Note that Krait venom is **not** neutralized by Neostigmine as effectively as Cobra venom because Krait toxins act pre-synaptically. 4. **Lethal Period:** Death usually occurs within 6 to 12 hours due to respiratory failure.

Q: What part of the nephron is primarily involved in arsenic poisoning?

Proximal Convoluted Tubule (PCT). **Explanation:** **1. Why Proximal Convoluted Tubule (PCT) is Correct:** Arsenic is a potent nephrotoxin that primarily targets the **Proximal Convoluted Tubule (PCT)**. The underlying mechanism involves arsenic’s high affinity for **sulfhydryl (-SH) groups**, which inhibits essential cellular enzymes. Because the PCT is the most metabolically active part of the nephron and is responsible for the bulk of reabsorption, it experiences the highest concentration of arsenic during excretion. This leads to mitochondrial dysfunction, oxidative stress, and subsequent **Acute Tubular Necrosis (ATN)**. Clinically, this manifests as oliguria, hematuria, and the presence of casts in the urine. **2. Why Other Options are Incorrect:** * **Loop of Henle:** While involved in the concentration of urine, it is not the primary site of toxic injury for heavy metals like arsenic. * **Distal Convoluted Tubule (DCT):** The DCT has lower metabolic activity and lower rates of solute reabsorption compared to the PCT, making it less susceptible to the direct toxic effects of arsenic. * **Collecting Duct:** This site is primarily involved in water reabsorption under the influence of ADH; it is rarely the primary site of damage in heavy metal poisoning. **3. NEET-PG High-Yield Pearls:** * **Classic Triad of Arsenic Poisoning:** Rice water stools (mimics Cholera), Garlic breath, and Aldrich-Mees lines (transverse white bands on nails). * **Skin Findings:** "Raindrop" pigmentation (hyperpigmentation) and hyperkeratosis of palms and soles. * **Antidote:** British Anti-Lewisite (BAL/Dimercaprol) is the drug of choice for acute poisoning. * **Mnemonic:** Remember **"P"** for **P**oisoning (Heavy metals) usually affects the **P**CT.

Q: Which of the following substances is known to cause tactile hallucinations?

Cocaine. **Explanation:** **Cocaine** is the correct answer because it is a potent central nervous system stimulant that can induce a specific type of tactile hallucination known as **Formication**. Patients experience a sensation of insects crawling under or over the skin. In forensic medicine and psychiatry, this is famously referred to as **"Magnan’s Symptom"** or **"Cocaine Bugs."** This phenomenon often leads to "skin picking," resulting in excoriations or "cocaine sores." **Analysis of Incorrect Options:** * **Opium (A):** An opioid analgesic and depressant. It typically causes euphoria, sedation, and miosis (pinpoint pupils). While it can cause vivid dreams or "opium visions," tactile hallucinations are not a characteristic feature. * **Cannabis (B):** Primarily a hallucinogen and deliriant. It is more commonly associated with distortions of time and space, or intensification of visual and auditory perceptions, rather than specific tactile hallucinations like formication. * **Cyanide (C):** A cellular toxin that inhibits cytochrome oxidase, leading to histotoxic hypoxia. Its effects are rapid and systemic (breath smelling of bitter almonds, seizures, and death); it does not cause chronic psychiatric symptoms like hallucinations. **High-Yield Clinical Pearls for NEET-PG:** * **Magnan’s Symptom:** Pathognomonic tactile hallucination associated with chronic cocaine abuse. * **Cocaine Triad:** Mydriasis, Tachycardia, and Hypertension (Sympathomimetic effect). * **Body Packers/Stuffers:** Individuals who swallow cocaine packets for smuggling; rupture can lead to fatal toxicity. * **Adulterant:** Cocaine is often "cut" with **Levamisole**, which can cause agranulocytosis and skin necrosis.

Question 1

Which of the following central nervous system depressants is most commonly used for suicidal purposes?

Accepted Answer

Opium

Answer

Cocaine

Answer

Lysergic acid diethylamide (LSD)

Answer

Cannabis

Question 2

Which condition affects the anterior horn cells?

Accepted Answer

Strychnine poisoning

Answer

Dhatura poisoning

Answer

Botulism

Answer

None of the above

Question 3

What is the antidote for belladonna poisoning?

Accepted Answer

Physostigmine

Answer

Neostigmine

Answer

Antihistamine

Answer

Atropine

Question 4

Black tongue and black teeth are seen in abuse of which substance?

Accepted Answer

Cocaine

Answer

Cannabis

Answer

LSD

Answer

Heroin

Question 5

Which poison resembles a viper snake bite?

Accepted Answer

Abrin

Answer

Ricin

Answer

Crotin

Answer

Bhi

Question 6

Which of the following poisons can be detected even from burnt bones?

Accepted Answer

Arsenic

Answer

OPC

Answer

LSD

Answer

Cyanide

Question 7

Which of the following substances is NOT cardiotoxic?

Accepted Answer

Opium

Answer

Aconite

Answer

Oleander

Answer

Nicotine

Question 8

What is the lethal dose of krait venom?

Accepted Answer

6 mg

Answer

3 mg

Answer

12 mg

Answer

15 mg

Question 9

What part of the nephron is primarily involved in arsenic poisoning?

Accepted Answer

Proximal Convoluted Tubule (PCT)

Answer

Collecting duct

Answer

Loop of Henle

Answer

Distal Convoluted Tubule (DCT)

Question 10

Which of the following substances is known to cause tactile hallucinations?

Accepted Answer

Cocaine

Answer

Opium

Answer

Cannabis

Answer

Cyanide

Forensic Toxicology — MCQs

Forensic Toxicology — MCQs

On this page

Practice by Chapter

Want unlimited practice?