BMS 113 · Common Core (Tronc commun)Section 6.1 · Prescription writing, dosage and safe medicine use
Section 26 of 31
The prescription and its three parts
Define a prescription, identify its superscription, inscription and subscription, and distinguish prescription-only from over-the-counter drugs.
New to this course? How each section works
Learn gives you one short idea at a time. Each idea starts with a single sentence, then explains it, gives an example, and asks you a small question you can answer straight away.
Explore shows a diagram of the same ideas. Click the numbered parts to read what each one is.
Check asks a few questions. Answer them all correctly to finish the section and unlock the next one.
“Go deeper” is optional. It adds mechanism and extra detail for when you are ready — nothing you need for the checks is hidden there.
Why this matters
If you cannot tell the three parts of a prescription apart, you cannot tell an order that is safe to dispense from one that is missing information the pharmacy needs. In practice that means a patient may receive the wrong amount, or a genuine order may be refused, because nobody can check who wrote it. You will meet this again in Unit 6.5, when you study the errors that actually reach patients.
What you need to know first
You only need everyday knowledge here: a pharmacist sells medicines, and some medicines need a doctor’s note while others can be taken from a shelf. Unit 5.2 explains the legal categories of drugs, and Unit 5.1 explains how drugs are grouped, but this section is the first place that shows you the document itself.
Words to know (6)
Prescription
A written order for medication from a licensed prescriber to a pharmacist, made for one named patient. A note naming one patient, one drug and one dose plan.
Superscription
The upper part of a prescription: the clinic, the date, the patient’s details and the Rx symbol. The clinic logo, the date and the patient’s age and sex.
Inscription
The middle part of a prescription, which carries the drug, its strength, its form and the whole dose plan. “Paracetamol 500 mg tablets, 2 three times a day for 3 days.”
Subscription
The last part of a prescription, which identifies the responsible prescriber by name, field, contact, signature and stamp. A signature and a stamp beside a named doctor.
Prescription-only medicine (PoM)
A drug that may be given only with a prescription because unsupervised use was judged unsafe, usually because its therapeutic window is narrow. Digoxin, because a small rise in its blood level can disturb the heart rhythm.
Over-the-counter (OTC) drug
A well-known drug judged safe for minor symptoms without medical supervision, usually because its therapeutic window is wide. A simple skin cream taken from an open shelf.
One idea at a timeIdea 1 / 6
In one sentence A prescription is a written order from a licensed prescriber to a pharmacist, made for one named patient.
A prescription is an order for one particular patient
A prescription is an order for medication from a licensed prescriber to a pharmacist, written for a particular patient. It is not a general recommendation: it names one patient, one drug and one plan of treatment. Because the pharmacist will act on it without seeing the patient, the information it carries must be precise, accurate, clear and readable. The lecture notes add three conditions that must be met before a prescription is written at all: prescribe only when necessary, carefully assess the balance of benefit and harm, and have a mastery of the drugs prescribed. A prescription is therefore the visible end of a clinical decision, never a substitute for one.
For example
A note that says “paracetamol for fever” without a dose, an interval or a duration is not a prescription: the pharmacist cannot calculate an amount, and the patient cannot know when to stop.
Think of it like
A prescription is like a signed work order for one address rather than a menu suggestion, but it differs in one way that matters: it must also record a clinical judgement, so it can never be copied for the next patient.
Pause and check yourself
Who is a prescription written for, and why does that matter?
Show the answer
It is written for one named patient, and it also fixes one drug and one plan of treatment, so the pharmacist knows exactly who is being treated and with what.
Read detailed explanations
Narrow and wide windows: why the law follows pharmacology
The therapeutic window is the gap between the maximum effective concentration and the minimum lethal concentration of a drug. When that gap is wide, ordinary variation in dose, absorption or timing is unlikely to move a patient from help into harm, so a well-known substance can be sold without a prescription and used on the basis of a clear label. When the gap is narrow, the same small variation is dangerous, so the drug is placed behind a prescription and often behind a monitoring plan. This is why the legal category is better understood as an output of pharmacology than as a separate rule: the PoM list is largely a list of drugs whose window, formulation or route makes unsupervised use unsafe. Digoxin, used in heart failure, is the standard narrow-window example, because a small rise in its blood level can cause nausea, visual disturbance and dangerous heart rhythms. The same logic explains two broad rules from the notes: all injectable drugs are prescription-only, because an injection bypasses the body’s usual barriers and cannot be undone easily, and all topical drugs are OTC, because most act locally at low systemic exposure. The practical consequence for a beginner is to stop treating “prescription-only” as an arbitrary inconvenience and to read it as a signal that the margin for error is small.
Precise, accurate, clear and readable: four qualities, four failures
The notes require the information on a prescription to be precise, accurate, clear and readable. These are not synonyms, and each one names a different way an order can fail. Precision means the order says exactly what is required and nothing vague: not “some” or “as needed” where a number is expected, but a stated dose, interval and duration. Accuracy means the values are correct for this patient: the right strength, the right number of units, the right interval, the right duration, with milligrams and micrograms not confused. Clarity means a competent reader reaches only one interpretation; ambiguity, not ignorance, is the usual cause of a wrong dose. Readability means the writing can actually be read — handwriting that forces the pharmacist to guess converts a clear intention into a lottery. Around these four qualities sit the dangerous abbreviations discussed in the next section, decimal points placed carelessly, and trailing zeros. A prescription can be clinically brilliant and still harm a patient if one of these four qualities is missing, which is why the notes treat them as requirements rather than as good manners. The pharmacist’s right and duty to contact the prescriber exists precisely because an order can fail on any one of the four, and the safe response is to ask rather than to assume.
Explore the diagram
Look at the whole drawing first. Then select one numbered part and connect it to the idea you just read.
The three parts of a prescription
A blank prescription divided into its three authenticating bands — superscription, inscription and subscription — with example content, patient instructions, prescriber identity and the PoM/OTC distinction.
New to diagrams? Read this first
Look at the whole drawing once without clicking anything. Ask yourself only: what kind of picture is this (a comparison, a route, a sequence, a table)?
Press Play, or use the arrows, to move through the numbered parts in order. The drawing stays still; only the highlight moves.
Click a number, or its name in the list below, to read what that part is and why it matters. Use “Hide labels” when you want to test your memory.
More controls
01 / 6Superscription
If the drawing is wider than this panel, scroll it sideways. Labels stay readable; the numbered explanations below show the same ideas.
Superscription
The upper part of the prescription, carrying the clinic name or logo, the date and the patient’s information — age, sex and disease details as they apply. It ends with the symbol Rx, read as “take thou”, the traditional instruction from prescriber to dispenser. This band identifies whom the medicine is for and when the order was written.
Schematic; not to scale. The blank form shows where each element belongs; real prescription layouts vary between clinics and countries, and the example content is illustrative.
Key points to remember
✓A prescription is an order for one named patient, not a general recommendation.
✓An authentic prescription has three parts: superscription, inscription and subscription.
✓The superscription says who and for whom, the inscription says what to give, and the subscription says who is responsible.
✓A missing part leaves a question that the pharmacy cannot answer alone, so the order is not usable.
✓Prescription-only or over-the-counter is the legal face of a safety judgement, usually the width of the therapeutic window.
Go deeper
Worked example
Deciding whether a prescription is authentic. Three slips arrive at the pharmacy on the same morning. Slip A carries a clinic logo, the date and the patient’s age and sex, but no drug information. Slip B carries a drug name, strength, formulation, dose and instructions, but the prescriber’s name, signature and stamp are missing. Slip C carries the clinic and patient block, the full drug and dose instruction, and the prescriber’s name, field, contact, signature and stamp.
Slip A has only the superscription. It identifies who and for whom, but it orders nothing, so no medicine can be dispensed from it.
Slip B has the inscription but not the subscription. The pharmacist cannot verify who is responsible, so the order is not authentic and must not be filled until it is confirmed.
Slip C has all three sections in order — superscription, inscription, subscription — and is the only authentic prescription of the three.
Because an authentic prescription is a legal document, the pharmacy also records what was dispensed and keeps the original, so the decision can be traced later if a question arises.
Authenticity is not decoration: each of the three sections answers a different question, and a missing section leaves a question that the pharmacy cannot answer alone.
Common misconception
A beginner often thinks a prescription is mainly a price note or a permission slip. It is a legal order that carries clinical decisions, and the pharmacist is bound by it rather than free to redesign it.
Check your reasoning
Why does the pharmacist need the subscription as much as the inscription, even when the drug and dose are perfectly clear?
Reveal an answer
Because the subscription identifies the responsible licensed prescriber. Without it the pharmacist cannot verify authenticity, cannot ask about an unclear or unsafe order, and cannot fix legal responsibility, so a clear-looking order may still be unusable.
Where this comes from
BMS 113 General Pharmacology I lecture notes · Prescription writing, pp. 52–55
Lesson progress is saved on this device for the current learner. Practice answers stay separate and are not stored.
About this course and its sources
Bilingual lessons organised from the supplied BMS 113 General Pharmacology I lecture notes. Diagrams are original educational schematics; pharmacology, nursing and French-language review are pending.