Drugs

The One Thing

Drugs alter chemical reactions or physiological processes in the body by interacting with biological targets such as receptors, enzymes or bacterial structures. Their benefits must be balanced against dose-dependent toxicity, side effects, dependence, misuse and, in the case of antibiotics, antibiotic resistance.

Reactions, Processes and Experiments

Key Terms

• Drug: A substance taken into the body that changes chemical reactions or physiological processes.
• Medicinal drug: A drug used to prevent, diagnose, control or treat a disease or condition.
• Misuse: Using a drug in an unsafe, illegal or inappropriate way, including taking too much or using a drug without medical need.
• Dose: The amount of a drug taken at one time or during a specified period.
• Receptor: A protein on or inside a cell to which a drug may bind, causing or blocking a response.
• Painkiller: A drug that reduces the sensation of pain; some strong painkillers can cause tolerance, dependence and respiratory depression.
• Antibiotic: A medicine that kills bacteria or stops them reproducing.
• Antiviral drug: A medicine that interferes with stages of viral reproduction; it does not generally kill viruses in the same way antibiotics kill bacteria.
• Antibiotic resistance: The ability of bacteria with resistance genes to survive an antibiotic and reproduce, making infections harder to treat.
• Tolerance: A condition in which repeated use causes a reduced response, so a larger dose is needed to produce the same effect.
• Dependence: A state in which the body or mind relies on a drug and stopping it may cause withdrawal symptoms.
• Withdrawal symptoms: Physical or psychological effects that occur when a dependent person reduces or stops taking a drug.
• Addiction: Compulsive drug use that continues despite harmful consequences and difficulty controlling use.
• Depressant: A drug that reduces activity in the central nervous system, often slowing reaction time, breathing and coordination.
• Stimulant: A drug that increases activity in the central nervous system, commonly raising alertness, heart rate and breathing rate.
• Hallucinogen: A drug that changes perception, mood and thought, sometimes causing hallucinations.
• Psychoactive drug: A drug that affects the brain and changes mood, behaviour, perception or consciousness.
• Placebo: A treatment without the active drug being tested, used as a comparison in clinical trials.
• Clinical trial: A controlled investigation used to test the safety, effectiveness and appropriate dose of a treatment in humans.
• Side effect: An unintended effect of a drug in addition to its desired medical effect.
• Therapeutic index: A comparison between a dose that produces a desired effect and a dose that causes harmful effects; a wider safety margin generally indicates a safer drug.

Easily Confused

• Antibiotics and antiviral drugs: Antibiotics target bacterial structures or processes, whereas antiviral drugs interfere with stages of viral reproduction.
• Antibiotics and viral disease: Antibiotics treat bacterial infections but do not cure viral diseases such as influenza.
• Tolerance and dependence: Tolerance means that a larger dose is needed for the same effect; dependence means that stopping the drug may cause withdrawal symptoms.
• Dependence and addiction: Dependence involves reliance on a drug and possible withdrawal, whereas addiction involves compulsive use despite harmful consequences and difficulty controlling use.
• Depressants and stimulants: Depressants reduce central nervous system activity, whereas stimulants increase it.
• Dose and toxicity: Increasing dose may increase the desired effect, but it may also increase toxicity, side effects and overdose risk.
• Placebo and medicinal drug: A placebo lacks the active drug being tested, whereas a medicinal drug contains an active treatment intended to produce a medical effect.
• Correlation and safety: A positive correlation between dose and effect does not show that every higher dose is safe; toxicity must also be measured.
• Smoking smoke damage and carbon monoxide action: Smoke damages airway cilia and increases respiratory infection risk, whereas carbon monoxide combines with haemoglobin and reduces oxygen-carrying capacity.
• Receptors and bacterial targets: Receptors are biological targets involved in cellular responses, whereas antibiotics may target bacterial cell wall formation or bacterial protein synthesis.

What Gets Asked

• Explain why medicinal drugs must be taken at the prescribed dose: The correct dose aims to produce a useful effect while limiting harmful effects; increasing the dose may increase toxicity, side effects or overdose risk.
• Compare antibiotics with antiviral drugs: Antibiotics act on bacterial structures or processes, while viruses reproduce inside host cells and lack the bacterial structures targeted by most antibiotics.
• Explain the development of antibiotic resistance: Antibiotic use creates selection pressure; susceptible bacteria die, while resistant bacteria survive and reproduce, increasing the frequency of resistance.
• Describe the effects of specific misused drugs: Alcohol can impair reaction time, coordination and judgement; nicotine and cocaine can increase alertness and heart rate; heroin can cause respiratory depression; cannabis can impair memory and judgement; anabolic steroids can cause liver, cardiovascular and reproductive problems.
• Interpret evidence from a clinical trial: Randomised controlled trials, comparison groups, repeated measurements, statistical analysis, placebos and, where appropriate, double-blind procedures help establish effectiveness while reducing expectations and researcher bias.
• Relate exposure to risk: Risk generally increases with dose, concentration, frequency or duration of exposure, but individual responses vary; a dose–effect correlation alone does not establish safety.