Genetic predisposition accounts for 40-60% of the vulnerability to addiction, highlighting its nature as a medical condition.
Factors like early exposure, trauma, and socioeconomic conditions play critical roles in the development of SUD.
Every addictive substance works by interacting with the brain's chemical signaling systems. Understanding pharmacology—how drugs affect the body at the molecular level—is essential for healthcare professionals managing addiction. This module explores neurotransmitter systems, receptor mechanisms, and how different drug classes produce their effects.
By the end of this module, you will be able to:
Function: Reward, motivation, motor control, attention
Key Pathways:
Role in Addiction:
Clinical Note: Dopamine is not simply "the pleasure chemical"—it more accurately signals motivational salience, driving us toward rewards both natural and drug-induced.
Function: Mood, sleep, appetite, impulse control, cognition
Role in Addiction:
Key Point: Low serotonin function is associated with impulsivity and aggression, which increase addiction risk.
Function: Primary inhibitory neurotransmitter; reduces neuronal excitability
Role in Addiction:
Clinical Pearl: GABA-ergic drug withdrawal (alcohol, benzodiazepines) can be life-threatening due to seizure risk. Always assess and medically manage.
Function: Primary excitatory neurotransmitter; involved in learning, memory
Role in Addiction:
Function: Pain modulation, stress response, reward
Role in Addiction:
Function: Alertness, arousal, stress response ("fight or flight")
Role in Addiction:
Function: Learning, memory, muscle activation, attention
Role in Addiction:
Receptor: Protein that binds specific molecules (ligands) and triggers cellular response
Ligand: Any molecule that binds to a receptor
Affinity: How strongly a ligand binds to a receptor
Efficacy: How much biological response a ligand produces once bound
| Type | Definition | Example | Clinical Use | |------|------------|---------|--------------| | Full Agonist | Binds receptor, produces maximum response | Heroin, Morphine, Fentanyl | Pain relief (but high abuse potential) | | Partial Agonist | Binds receptor, produces submaximal response | Buprenorphine | MAT for opioid use disorder | | Antagonist | Binds receptor, blocks response | Naloxone, Naltrexone | Overdose reversal, relapse prevention | | Inverse Agonist | Binds receptor, produces opposite response | Some GABA compounds | Research applications |
Partial agonists have a "ceiling" beyond which increased dose does not increase effect:
Buprenorphine Example:
Absorption: How drug enters bloodstream
Distribution: How drug spreads through body
Metabolism: How body breaks down drug
Elimination: How drug leaves body
| Drug | Route | Half-life | Withdrawal Onset | |------|-------|-----------|------------------| | Heroin | IV/Smoked | 30 min | 6-12 hours | | Fentanyl | IV/Smoked | 3-4 hours | 4-6 hours | | Oxycodone | Oral | 3-4 hours | 8-12 hours | | Methadone | Oral | 24-36 hours | 24-48 hours | | Buprenorphine | Sublingual | 24-42 hours | 24-72 hours |
Clinical Pearl: Longer-acting medications like methadone and buprenorphine produce more stable blood levels, reducing cycles of intoxication and withdrawal.
Receptors: Mu (μ), Kappa (κ), Delta (δ)
Mechanism:
Tolerance Mechanism:
Withdrawal Mechanism:
Cocaine Mechanism:
Methamphetamine Mechanism:
Amphetamine (Adderall) Mechanism:
Multiple Mechanisms:
| System | Effect | Result | |--------|--------|--------| | GABA-A | Enhanced | Sedation, anxiolysis | | NMDA Glutamate | Inhibited | Impaired memory, coordination | | Dopamine | Increased (indirect) | Reward, reinforcement | | Serotonin | Modulated | Mood effects | | Opioid | Endorphin release | Euphoria |
Withdrawal Danger:
Mechanism:
Cross-Tolerance with Alcohol:
Danger of Combination:
Mechanism:
Rapid Tolerance:
Mechanism:
Endocannabinoid System:
| Combination | Mechanism | Risk | |-------------|-----------|------| | Opioids + Benzodiazepines | Synergistic CNS depression | Respiratory arrest | | Opioids + Alcohol | Same | Respiratory arrest | | Cocaine + Alcohol | Forms cocaethylene | Cardiotoxicity | | Stimulants + MAOIs | Tyramine reaction | Hypertensive crisis | | MDMA + SSRIs | Serotonin excess | Serotonin syndrome |
When prescribing for patients with addiction history:
Priya, 28, presents to the emergency department after a witnessed seizure. Her roommate reports she has been drinking heavily for years but stopped suddenly 3 days ago when she ran out of money. She also takes alprazolam (Xanax) prescribed by another doctor for anxiety.
Discussion Questions:
Next Module: Risk Factors: Genetics, Epigenetics & Adverse Childhood Experiences →
External links
Use one of the external tools below to explore "The Chemistry of Addiction: Pharmacology & Mechanisms". Check clinical claims against approved sources.
External links
Use one of the external tools below to explore "The Chemistry of Addiction: Pharmacology & Mechanisms". Check clinical claims against approved sources.