Check your medicines for interactions

How to use the checker

Enter the names of the medicines, supplements, or vitamins you take regularly or occasionally. You can also add foods, such as grapefruit, or conditions, such as pregnancy, to get more relevant results. To run an interaction check, you’ll need to add at least two items.

Once everything is entered, select Check now to view the results and any potential interactions identified.

A drug interaction occurs when one medicine affects how another medicine works in the body. This can change how effective a treatment is, increase the risk of side effects, or lead to unexpected health problems.

Drug interactions can happen in:

• Prescription medicines.

• Over-the-counter treatments.

• Supplements.

• Herbal remedies.

• Foods.

• Alcohol.

• Certain medical conditions.

Some interactions are mild and simply need monitoring, while others may require changes to the dose, timing, or choice of medicine. Checking for interactions helps reduce avoidable risks and supports safer use of medicines.

Drugs interact because of how the body absorbs, processes, and responds to medicines. Some medicines affect how others are broken down in the liver, which can increase or reduce the amount of medicine in the bloodstream. Others influence how medicines are absorbed from the gut or removed by the kidneys.

Interactions can also occur when medicines have similar effects on the body. For example, taking two medicines that both cause drowsiness can increase the risk of excessive sedation.

The likelihood of interactions increases with the number of medicines taken, as well as with age and long-term health conditions.

The most common types of drug-drug interactions are:

• Where one medicine increases the side effects of another.

• Where one medicine reduces how well another works.

• Those that alter how quickly a drug is processed in the body.

Some interactions increase the risk of bleeding, particularly when medicines that affect clotting are taken together. Others may affect heart rhythm or blood pressure. These types of interactions are well recognised and often form the basis of safety warnings and prescribing guidance.

Symptoms of a drug interaction vary depending on the medicines involved and the person taking them.

Common symptoms include:

• Dizziness.

• Drowsiness.

• Confusion.

• Headaches.

• Feeling sick (nausea).

• Stomach pain.

• Palpitations.

• Changes in mood.

Symptoms often appear after starting a new medicine, changing a dose, or adding a supplement or herbal product.

Some medicines are more likely than others to be involved in interactions. These include:

• Blood-thinning medicine (anticoagulants).

• Anti-inflammatory painkillers.

• Certain antidepressants.

• Antibiotics and antifungals.

• Medicines that act on the brain or nervous system.

• Supplements and herbal remedies.

The most dangerous drug combinations are those that can cause serious harm if taken together. These often involve:

• Medicines that slow breathing or affect alertness.

• Medicines that significantly increase bleeding risk.

• Medicines that can disrupt heart rhythm.

Some medicines also have a narrow safety margin, meaning that small changes in dose or blood level can lead to serious side effects.

If a severe interaction is identified, it is important not to stop medicines suddenly without advice. A pharmacist or doctor can help decide the safest next steps.

Certain foods are known to interact with medicines. Common food and drug interactions include:

• Grapefruit and grapefruit juice - can affect how some medicines are broken down, leading to higher levels in the body.

• Alcohol - can increase side effects such as drowsiness, dizziness, and stomach irritation with many medicines.

• Foods high in calcium - can reduce the absorption of some medicines if taken at the same time,

• Foods rich in vitamin K - can affect the action of certain blood-thinning treatments.

Including foods in an interaction check can help highlight these potential issues.

Some medicines can be taken together safely, but others work better if they are taken at different times. This may be to prevent interactions in the stomach, reduce side effects, or ensure medicines are absorbed properly.

The timing of medicines can also depend on whether they should be taken with food or on an empty stomach. If you take several medicines each day, a pharmacist can help you create a schedule that is both safe and practical.

You can reduce the risk of drug interactions by:

• Keeping an up-to-date list of all medicines, supplements, and vitamins you take and sharing it with healthcare professionals.

• Checking for interactions before starting new treatments, including over-the-counter medicines and supplements.

• Following advice about food, alcohol, and timing, and try to use the same pharmacy where possible so your medicines can be reviewed together.

• Always telling healthcare professionals if you are pregnant, breastfeeding, or have long-term health conditions when discussing medicines.