3 Clinical psychopharmacology3.1 General pharmacology
3.1.7 Principles of rational prescribing
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Written by Resident Doctor Committee · Published
Defining the problem
Rational prescribing means prescribing for a defined purpose, weighing benefit, harm, burden and alternatives, then reassessing that balance during treatment.
A symptom or diagnosis does not by itself justify medication.
Agitation needs its cause sought first: pain, retention, delirium, substances or akathisia.
Urgent risk may justify treating while assessment continues.
Benefit in absolute terms
Absolute risk shows real benefit: halving an annual relapse risk of 2% prevents one event per 100 people, but halving 60% prevents 30.
Outcomes, when to expect them and what justifies continuing should be agreed at the start.
Estimating harm
Each harm is judged by how likely, severe, reversible and detectable it is.
Harm | Onset |
|---|---|
Acute dystonia, postural hypotension | Often early |
Metabolic harm | Can begin within weeks and accumulates |
Tardive dyskinesia | Usually after longer exposure, so examine regularly |
Factor | Risk it adds |
|---|---|
Age and frailty | Sensitivity, accumulation, falls |
Physical illness | Cardiac, renal, hepatic, metabolic or seizure risk |
Childbearing potential | Reproductive risk, set against the risk of untreated illness |
Previous reactions, the best predictor | Recurrence of the same adverse reaction |
Overdose and substances | Lethality, co-intoxication, quantity supplied |
Co-prescribed medicines | Kinetic interactions, additive toxicity |
Clozapine can justify substantial monitored risks in the right patients, but contraindications and specialist safeguards still apply.
Consent and starting treatment
Montgomery defines a material risk as one significant to a reasonable person in the patient's position, or known to matter to this individual.
Disagreement with the prescriber does not establish incapacity.
Preferences affect treatment success, so burdens such as weight gain are discussed alongside medical risks.
Patients need urgent advice on infection symptoms with clozapine, rash with lamotrigine and signs of lithium toxicity.
The plan states the starting dose, target, titration, review date, trial length and taper, and who monitors.
Reassessment after an adequate trial
Before calling a drug a failure, check dose, duration, adherence, interactions, substances and diagnosis.
Natural improvement should be considered before the drug is credited.
Pattern | Features |
|---|---|
Withdrawal | Often begins after dose reduction, may bring new physical symptoms and can persist |
Rebound | Original symptoms return temporarily intensified |
Relapse | Underlying illness returns, with variable timing |
These are told apart by timing, symptom pattern and course.
Polypharmacy and cascades
Each added drug increases interactions and cumulative adverse-effect burden, so combinations need evidence and a defined target.
Prescribing cascades should be checked for, because akathisia, parkinsonism or anticholinergic effects can be mistaken for new illness.
Treatments continued after a temporary indication has resolved should be reviewed.