BMS 113 · Common Core (Tronc commun)Section 5.2 · Classification of drugs and major drug classes
Section 23 of 31
Prescription, OTC and controlled drugs
Distinguish prescription-only, over-the-counter and controlled drugs and explain the safety reason behind each category.
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Why this matters
If you do not know which legal category a medicine belongs to, you may supply it without the prescription or the record the law requires, and the patient carries the risk. These categories come back whenever a later example reaches the pharmacy counter.
What you need to know first
You should already know that one drug can have a generic and a trade name. Unit 4.5 explains how the choice of route changes the risk of a medicine.
Words to know (5)
Prescription drug (legend drug)
A medicine that may legally be supplied only with a written order from a licensed prescriber. An antibiotic usually needs a written order before the pharmacist may dispense it.
Over-the-counter (OTC) drug
A medicine sold directly to the public without a prescription, intended for minor symptoms. Paracetamol for a mild headache can be taken from the shelf.
Controlled substance
A medicine with a high potential for abuse, kept under extra legal control of prescribing, storage and recording. Morphine is stored under lock and every dose is recorded.
Therapeutic window
The gap between the dose that works and the dose that becomes dangerous. A narrow window means a small increase can turn a helpful dose into a harmful one.
Prescriber
The health professional who is legally allowed to write an order for a medicine. A pharmacist may dispense a controlled drug only on a prescriber’s order.
One idea at a timeIdea 1 / 4
In one sentence A prescription drug may be supplied only when a licensed prescriber has written an order for it.
Prescription drugs require a written order
A prescription drug may be supplied only on a written order from a physician or another licensed prescriber. Most prescription drugs are designated by the FDA, the United States Food and Drug Administration, although individual states can also designate specific drugs or devices as prescription items. They may be dispensed only by a pharmacist, by a pharmacy technician working under a pharmacist, or by the prescriber. They are also called legend drugs, from the label required on packaging to warn that they may be sold only on prescription.
For example
A patient who wants an antibiotic for a sore throat cannot simply buy it: the pharmacist must have a written order from a licensed prescriber before dispensing.
Pause and check yourself
Who may legally dispense a prescription drug?
Show the answer
Only a pharmacist, a pharmacy technician working under a pharmacist, or the prescriber who wrote the order.
Read detailed explanations
What the therapeutic window really measures
The therapeutic window is the gap between the maximum effective concentration and the minimum lethal concentration. “Maximum effective” describes the level above which more drug adds little benefit, and “minimum lethal” the level at which the drug begins to kill. A drug with a wide window can be taken by many people in slightly different doses without disaster; a drug with a narrow window can help at one concentration and harm at another only slightly higher. Three practical consequences follow. First, narrow-window drugs are usually prescription-only and may require measurement of the concentration in the blood, because the prescriber cannot infer the level reliably from the dose alone. Second, anything that changes how the body handles the drug becomes important: reduced kidney or liver function, dehydration, or another medicine that slows metabolism can push a safe level into the toxic range. Third, the window is a population average, not a personal guarantee; age, weight, genetics and disease shift it for each patient. This is why the same medicine can be routine for one person and need close monitoring in another, and why the legal category is a starting point for supervision rather than a substitute for it.
Why injectables and topicals sit at opposite ends
The notes state that, as a rule, all injectable drugs are prescription-only while all topical drugs are OTC. The reason lies in what happens after administration. An injection places the drug directly into the body, often into the bloodstream, bypassing the barriers of skin and gut. Absorption is rapid and often complete, the full dose arrives at once, and if the dose is wrong there is little time to remove it. Injectables must also be sterile, are usually given by trained personnel, and carry a higher risk of side effects that require close monitoring. Topical drugs, by contrast, are applied to the skin or mucous membranes, usually for local effects; only a fraction is absorbed into the general circulation, the effect is largely confined to the place of application, and an error can often be washed off. These are general tendencies rather than absolute laws. A transdermal patch is applied to the skin yet delivers drug into the bloodstream for systemic action, and a corticosteroid cream used over a large area or under an occlusive dressing can be absorbed enough to produce systemic effects. The legal category tells you the usual risk of the group; the product and the patient tell you the actual one.
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Prescription, OTC and controlled drugs
The law places medicines in three practical categories, and the width of the therapeutic window explains why one of them needs a written order.
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01 / 5Prescription (legend) drugs
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Prescription (legend) drugs
A prescription or legend drug can be dispensed only on a written order from a physician or another licensed prescriber, and only by a pharmacist, a technician under a pharmacist’s direction, or the prescriber. Such drugs usually have a narrow therapeutic window, so the dose must be supervised. Digoxin is the classic example, and all injectables are prescription-only as a rule.
Schematic; not to scale. The three categories are the ones used in the lecture notes; national law may add further classes and local rules.
Key points to remember
✓Prescription drugs need a written order and are also called legend drugs.
✓OTC drugs are sold without a prescription because long use has shown a wide margin of safety, but they are not risk-free.
✓Controlled substances have a high potential for abuse and carry extra rules on prescribing, storage and recording.
✓The legal category follows the width of the therapeutic window; injectables are usually prescription-only and topicals usually OTC.
Go deeper
Worked example
Sorting four requests at the pharmacy counter. During one morning, four people come to the pharmacy counter: a man asking for a cream for dry skin; a woman with a written order for an antibiotic; a student asking for a strong painkiller that contains a narcotic; and a person asking for something for a mild headache.
The dry-skin cream is a topical product sold over the counter; give brief advice on use and on when to consult a clinician if it does not improve.
The antibiotic is a prescription-only legend drug; check that the written order is complete and authentic and that the prescriber is licensed before dispensing.
The narcotic painkiller is a controlled substance; it needs a physician’s prescription and the additional recording and storage rules that apply to controlled drugs.
The mild headache calls for an OTC medicine; sell it with the instruction to respect the label and to avoid combining several products that contain the same active ingredient.
The four products are all medicines, yet the law treats them differently because their potential for harm differs. The category tells the pharmacy who may receive the product, on what authority, and with what warnings.
Common misconception
A common beginner belief is that “over the counter” means safe for everyone and free of side effects. The notes warn the opposite: OTC drugs have a wide margin of safety, but if patients do not follow the instructions they can still cause serious side effects.
Check your reasoning
Why does a narrow therapeutic window usually lead to a prescription-only category?
Reveal an answer
Because when the useful concentration and the dangerous concentration are close, a small error in dose, in kidney or liver function, or in another medicine taken at the same time can cause harm. Supervision by a prescriber and pharmacist, and sometimes measurement of blood levels, reduces that risk, whereas a wide window makes unsupervised use more acceptable.
Where this comes from
BMS 113 General Pharmacology I lecture notes · Unit 5, pp. 19–20 and pp. 53–54
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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.