Contraindications vs. warnings on a medicine label

Updated 2026-10-09 · Reviewed for accuracy by the EKO Labs team. Educational only; not medical advice.

The FDA-approvedFDA-approved the FDA reviewed the medicine's safety and effectiveness for a specific use. prescribing informationPrescribing information (label) the official FDA document for a medicine, with its uses, warnings and side effects. (the full “label”) of a U.S. prescription medicine has fixed sections in a fixed order. Four of them are about safety and are easy to mix up: Contraindications, Warnings and Precautions, Adverse Reactions and Drug Interactions. This guide explains what each one means and how they differ, using real examples from GLP-1GLP-1 (glucagon-like peptide-1) a hormone the gut releases after eating. It helps release insulin, slows stomach emptying and signals fullness. medicine labels. It is general information, not medical advice; your prescriber decides what is right for you.

Do not stop or change a prescribed medicine on your own because of something you read on a label. Talk to your prescriber or pharmacist first. In an emergency, call 911.

Where these sections are

Under federal rules (21 CFR 201.57), the full prescribing information starts with a short “Highlights” summary and, when FDA requires one, a boxed warningBoxed warning the FDA's strongest warning, printed in a box on a medicine's label. GLP-1 medicines carry one about thyroid C-cell tumors.. After that come numbered sections, including:

• 4 Contraindications
• 5 Warnings and Precautions
• 6 Adverse Reactions
• 7 Drug Interactions
• 8 Use in Specific Populations (pregnancy, lactation, people who could become pregnant, children, older adults)
• 17 Patient Counseling Information

Because the numbers are the same on every label in this format, you can jump straight to section 4 or 5 on any medicine. You can read the current label for free on DailyMed or Drugs@FDA.

Contraindications (section 4): when the medicine should not be used

A contraindicationContraindication a reason a person should not take a medicine. is a situation in which a medicine should not be used because the risk clearly outweighs any possible benefit. The rule says only known hazards may be listed, not theoretical ones, and if none are known the section must say “None.”

Example: the labels of Ozempic®, Mounjaro®, Trulicity® and Victoza® list two contraindications:

• a personal or family history of medullary thyroid carcinomaMedullary thyroid carcinoma (MTC) a rare thyroid cancer. People with a personal or family history should not use GLP-1 medicines. (MTC), or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2MEN 2 multiple endocrine neoplasia type 2, an inherited condition that raises the risk of MTC.);
• a prior serious hypersensitivity (allergic) reaction to the medicine or to any of its ingredients.

This is why your prescriber asks about your own and your family's thyroid history and about past allergic reactions before prescribing.

Warnings and Precautions (section 5): serious risks to watch for

This section describes clinically significant risks: reactions that can be serious even if they are rare, or that can be prevented or reduced with the right use, plus what should be done if they happen. A warning does not mean you cannot take the medicine. It means you and your care team should know the risk, watch for its signs and sometimes do extra checks. The rule also says a warning must be added as soon as there is reasonable evidence that the medicine is linked to a hazard; proof of cause is not required.

Examples from recent GLP-1 labels (each label differs, so read the one for your medicine):

• Acute pancreatitis: the medicine is stopped if pancreatitisPancreatitis inflammation of the pancreas. Severe stomach pain that does not go away needs urgent care. is suspected.
• Low blood sugar (hypoglycemia) when used together with insulinInsulin the hormone that moves sugar from the blood into the body's cells. or medicines that make the body release insulin, such as sulfonylureas; the doses of those medicines may need to be lowered.
• Acute kidney injury linked to dehydration from vomiting or diarrhea.
• Serious allergic reactions, gallbladder problems, and diabetic retinopathy complications (eye) on some labels.
• Pulmonary aspiration during general anesthesia or deep sedation: patients are asked to tell their health care providers about any planned surgery or procedure.

Adverse Reactions (section 6): side effects seen with the medicine

This section lists side effects for which there is some reason to believe the medicine caused them, often with how often they happened in clinical trials. It is usually the longest list. Common does not mean serious, and serious does not mean common: for example, nausea may be listed as common in section 6, while pancreatitis is less common but appears in section 5 because it is serious.

Drug Interactions (section 7)

This section covers important interactions with other prescription or over-the-counter medicines, supplements or foods, and practical steps to prevent or manage them. Bring a complete list of everything you take, including vitamins and herbal products, to every visit.

Contraindication vs. warning: the short version

• Contraindication = should not be used in that situation.
• Warning / precaution = may be used, but with awareness, monitoring or changes to other treatment.
• Adverse reaction = a side effect that may happen; check how often and how serious.
• Boxed warning = the most serious warnings, shown in a box at the top of the label.

Patient-friendly versions

Many medicines also have a Medication Guide or Patient Information leaflet written in plain language. If your medicine has a Medication Guide, the pharmacy must give it to you. Compounded medicines do not have FDA-approved labeling, so ask your prescriber or pharmacist which safety information applies.

Questions for your prescriber or pharmacist

• Does anything in my health history, or my family's, make this medicine a poor fit for me?
• Which warnings matter most for me, and which symptoms mean I should call you?
• Does this medicine interact with anything else I take?
• Should I tell my surgeon or dentist that I take it before a procedure?
• Can you go over the Medication Guide with me in a language I understand?

If you have a side effect, tell your prescriber; you can also report it to the FDA through MedWatch. At EKO Labs, our team answers questions in Portuguese or English by phone.

Sources: 21 CFR 201.57(a) and (c)(5)–(9), (c)(18) (format and content of prescribing information: contraindications, warnings and precautions, adverse reactions, drug interactions, specific populations, patient counseling; eCFR, current as of October 2026); 21 CFR 208.24 (Medication Guide distribution); FDA-approved prescribing information for Ozempic®, Mounjaro®, Zepbound®, Wegovy®, Trulicity® and Victoza® (openFDA drug labeling / DailyMed, accessed October 2026). This guide is general information, not medical advice.