A symptom, condition, or trait that interferes with a given drug or treatment in a dangerous or counterproductive way. Most drugs and medical treatments have contraindications. For example, if drug A interacts with drug B, the labeling for drug A will list drug B as a contraindication. This means that people taking drug B should not take drug A. Some drugs can cause harm to people who have liver or kidney disease; for these drugs, these conditions are contraindications, or reasons not to take the drugs. Pregnancy is a contraindication for many drugs, either because the drug can harm the unborn fetus, or because its effects on the fetus are unknown.

Even over-the-counter remedies can have contraindications. For example, the dietary supplement glucosamine, which is reported to ease the symptoms of osteoarthritis, may be contraindicated in people with diabetes because it has been shown to increase insulin resistance, which can raise blood glucose levels.

When your doctor prescribes a drug or treatment, he or she should be aware of the contraindications and consider whether they apply to you. To protect yourself, you should be sure that all your doctors know about your diabetes, any other medical conditions you may have, and any drugs that you are taking. Remember also to read the labels on all prescription and over-the-counter drugs before you take them to see if they have any warnings about diabetes or any other contraindications that apply to you.