Unit 5: Drugs Acting on Central Nervous System (Part II)

March 3, 2026

Semester 4
BP404T

Introduction to Drugs Acting on Central Nervous System (Part II)

This final unit ventures into Psychiatry and severe CNS pathology. It explores Psychopharmacological agents: the antipsychotics used for schizophrenia, the antidepressants (like SSRIs) used for clinical depression, and lithium for bipolar mania. It examines the neurodegenerative drug strategies for Parkinson’s Disease (focusing on the Levodopa/Carbidopa synergy) and Alzheimer’s disease. Finally, it details the heavy-hitting Opioid Analgesics, explaining how drugs like Morphine destroy severe pain, their dangerous side-effect of respiratory depression, and how to reverse accidental overdoses using Naloxone.

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Syllabus & Topics

  • 1Antipsychotics: Typical (Haloperidol) and Atypical (Clozapine, Olanzapine).
  • 2Antidepressants: TCAs, MAOIs, SSRIs, SNRIs.
  • 3Anti-manic drugs: Lithium carbonate.
  • 4Pharmacology of Parkinson’s disease: Levodopa, Carbidopa, MAO-B inhibitors.
  • 5Pharmacology of Alzheimer’s disease: Cholinesterase inhibitors, Memantine.
  • 6CNS stimulants and Nootropics (Cognitive enhancers).
  • 7Opioid analgesics (Morphine, Fentanyl, Methadone) and Antagonists (Naloxone).

Learning Objectives

Identify the neurotransmitter pathways implicated in Schizophrenia and Depression.
Detail the blood-brain barrier mechanics that make Levodopa therapy unique.
Understand the progression of Alzheimer’s and the drugs slowing its symptoms.
Evaluate the therapeutic use, dependence liability, and overdose treatment of Opioid narcotics.

Frequently Asked Questions (FAQs)

Q1. What is the Primary Mechanism of Typical Antipsychotics?

Typical antipsychotics such as Haloperidol and Chlorpromazine act primarily as antagonists at dopamine D2 receptors in the mesolimbic and mesocortical pathways of the brain. By blocking excessive dopamine activity, they reduce the positive symptoms of schizophrenia, including hallucinations and delusions.

Q2. How Do SSRI Antidepressants Work?

Selective Serotonin Reuptake Inhibitors (SSRIs) such as Fluoxetine inhibit the Serotonin transporter (SERT), which is responsible for reuptake of serotonin into the presynaptic neuron. This increases serotonin levels in the synaptic cleft, prolonging stimulation of postsynaptic receptors and improving mood.

Q3. What is the Pharmacological Strategy for Treating Parkinson’s Disease?

Parkinson’s disease results from degeneration of dopamine-producing neurons, leading to dopamine deficiency and relative acetylcholine excess. Treatment strategies include increasing dopamine levels using Levodopa (which crosses the blood–brain barrier) combined with Carbidopa to prevent peripheral metabolism, or using central anticholinergic agents to reduce excessive cholinergic activity.

Q4. Why Are Strong Opioids Carefully Regulated?

Strong opioids such as Morphine act on μ-opioid receptors to provide potent analgesia. However, they carry significant risks, including severe respiratory depression (a major cause of overdose fatalities) and high potential for psychological and physical dependence, necessitating strict regulation and monitoring.