Drugs & Society Chapter 5.1

How and Why Drugs Work

Chapter 5

Wednesday: Would you rather….

A. Find true love

B. Find $10,000,000.00

Find tr

ue love

Find $10

,000,00

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0%0%Response

Intended and Unintended Effects of Drugs

• Intended responses:

• Reason for using the drug• Unintended responses:

• Side effects• The main distinction between intended responses and side

effects depends on the therapeutic objective.

Common Side Effects of Drugs

• Nausea or vomiting

• Changes in mental alertness

• Dependence

• Withdrawal• Allergic reactions

• Changes in cardiovascular activity

Common Side Effects of Drugs

Dose-Response

• Many factors can affect the way an individual responds to a drug, including the following:

• Dose

• Tolerance

• Potency

Dose-Response (continued)

• Additional factors

• Pharmacokinetic properties:

• Rate of absorption

• Manner distributed throughout the body

• Rate metabolized and eliminated

• Form of the drug

• Manner in which the drug is administered

Potency vs. Toxicity

• Potency: The amount of drug necessary to cause an effect

• Toxicity: The capacity of a drug to do damage or cause adverse effects in the body

Margin of Safety

• The range in dose between the amount of drug necessary to cause a therapeutic effect and a toxic effect.

Drug Interaction• Additive effects

• Summation of effects of drugs taken concurrently

• Antagonistic (inhibitory) effects

• One drug cancels or blocks effects of another

• Potentiative (synergistic) effects

• Effect of a drug is enhanced by another drug or substance

Pharmacokinetic FactorsThat Influence Drug Effects

• Administration

• Absorption

• Distribution

• Inactivation

• Biotransformation and elimination

Forms and Methods of Taking Drugs

• Oral ingestion• Inhalation• Injection• Topical application

Distribution

Distribution

• Most drugs are distributed throughout the body in the blood.

• It takes approximately 1 minute for a drug to circulate throughout the body after it enters the bloodstream.

• Drugs have different patterns of distribution depending on their chemical properties.

Required Doses for Effects

• Threshold dose: The minimum amount of a drug necessary to have an effect

• Plateau effect: The maximum effect a drug can have regardless of the dose

• Cumulative effect: The buildup of drug concentration in the body due to multiple doses taken within short intervals

Time-Response Factors

• The closer a drug is placed to the target area, the faster the onset of action.

• Acute drug response:

• Immediate or short-term effects after a single drug dose

• Chronic drug response:

• Long-term effects after a single dose

Biotransformation

• Biotransformation: The process of changing the chemical or pharmacological properties of a drug by metabolism.

• The liver is the major organ that metabolizes drugs in the body.

• The kidney is the next most important organ for drug elimination.

Physiological Variables That Modify Drug Effects

• Age

• Gender

• Pregnancy

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Adaptive Processes

Tolerance• Reverse tolerance (sensitization): Enhanced response to a

given drug dose; opposite of tolerance

• Cross-tolerance: Development of tolerance to one drug causes tolerance to related drugs

• Physiological or Pharmacological tolerance: Changes causing decreased response to a set dose of a drug

• Behavioral tolerance: Drug may have the same biochemical effect but a reduced behavioral effect as a drug user learns to compensate for nervous system impairment

Drug Dependence

PhysicalDependence

(e.g.,withdrawal and rebound,

tolerance)

PsychologicalDependence

(e.g., craving, preoccupation)

Psychological Factors AffectingDrug Effect

• Individual’s mental set

• Setting or environment

• Placebo effects

Addiction and Abuse

• The use of the term addiction is sometimes confusing. It is often used interchangeably with dependence, either physiological or psychological in nature; other times, it is used synonymously with the term drug abuse. A more accurate definition is the compulsive drug use despite negative consequences.

Addiction and Abuse (continued)

• Factors affecting variability in dependence/addiction:

• Hereditary factors (genetic variants); responsible for 40–60% vulnerability

• Drug craving

Addiction and Abuse (continued)

• Other factors contributing to drug use patterns:

• Positive versus negative effects of drug

• Peer pressure

• Home, school, and work environment

• Mental state