Poisoning emergencies present unique challenges in medical practice, requiring swift and accurate intervention to mitigate harm. Among the arsenal of treatments available, activated charcoal is a potent tool for managing certain types of poisonings. 

Activated charcoal is a common exam topic, both in undergraduate and postgraduate exams, so understanding its mechanisms, indications, and administration is pivotal for doctors and medical students gearing up for examinations and real-world scenarios alike. 

Here are some essential exam tips to help grasp the intricacies of activated charcoal usage in poisoning cases.

Grasping the basics

Activated charcoal, a highly porous form of carbon, is a commonly used decontamination agent used in poisoning. It acts by absorbing molecules of the ingested toxin on its surface in the gastrointestinal tract before they can be absorbed into the bloodstream. This mechanism prevents further systemic toxicity, making it a valuable intervention in acute poisonings.

Activated charcoal is the chemically inert form of carbon. It is an odourless, tasteless, fine black powder prepared by pyrolysis of carbonaceous matter and then concentrated with a zinc chloride solution. This process forms an internal maze of pores with an absorptive area of approximately 3,000 m2/g that can inhibit the absorption of the offending toxin by as much as 50%. 

Timing is crucial

In exams, expect questions on when to administer activated charcoal. Remember, its effectiveness hinges on early intervention and the efficacy of activated charcoal diminishes as time passes after ingestion. Optimal outcomes are achievable when administration occurs promptly, ideally within the first hour following ingestion. While still beneficial within two hours, its efficacy wanes after that.

Dosage, administration, and contraindications

Dosage calculations often feature prominently in exams. The usual dose is 50 g for adults and 1 g/kg for children. It is usually administered as a slurry either orally or via a nasogastric tube. Adequate mixing with water to form a suspension is crucial to enhance its adsorptive surface area.

While activated charcoal is generally safe, certain scenarios warrant caution or avoidance. The patient should be co-operative, and activated charcoal should not be used if:

  • There is impairment of consciousness or coma (risk of aspiration)
  • Seizures are thought to be imminently likely (risk of aspiration)
  • There is reduced gastrointestinal motility (risk of obstruction)

In addition, its use should be avoided in cases of ingestion of corrosive substances such as strong acids and alkalis as it may exacerbate mucosal injury.

When to use activated charcoal

Activated charcoal is useful in overdose with the following drugs/toxins:

  • Aspirin
  • Paracetamol
  • Barbiturates
  • Tricyclic antidepressants
  • Digoxin
  • Amphetamines
  • Morphine
  • Cocaine
  • Phenothiazines

Activated charcoal is ineffective in overdose with the following drugs/toxins:

  • Iron
  • Lithium
  • Boric acid
  • Cyanide
  • Ethanol
  • Ethylene glycol
  • Methanol
  • Malathion
  • DDT
  • Carbamate
  • Hydrocarbon

Adverse effects associated with activated charcoal usage

Possible adverse effects include the following:

  • Nausea and vomiting
  • Diarrhoea
  • Constipation
  • Bezoar formation
  • Bowel obstruction
  • Pulmonary aspiration
  • Direct administration to the lung via NG tube (potentially fatal)
  • Impaired absorption of oral medications/antidotes

Monitoring after administration

After administering activated charcoal, diligent monitoring of the patient’s clinical status is imperative. Serial assessments of vital signs, mental status, and laboratory parameters aid in gauging response to treatment. Additionally, consider the need for decontamination techniques such as gastric lavage and bowel irrigation, and adjunct therapies based on the specific toxin involved.

Integrating clinical decision-making

It is important to remember that poison management is rarely straightforward, often requiring nuanced decision-making based on clinical judgment and toxin-specific factors. Medical exams may present complex case scenarios demanding prioritisation of interventions, recognising red flags, and formulating comprehensive treatment plans.


Mastering the use of activated charcoal in poisoning cases is essential for medical students and doctors preparing for exams and future clinical practice. By grasping its mechanisms, indications, dosing, administration techniques, and associated considerations, you will be better equipped to navigate poison-related scenarios with confidence and proficiency. Remember, effective poison management hinges on not just technical knowledge but also empathetic patient care and interdisciplinary collaboration.


Thank you to the joint editorial team of www.mrcemexamprep.net for this months ‘Exam Tips’ post.