How to Check Drug Interactions

Why drug interactions matter

A drug interaction occurs when one medication affects the action of another. This can make a drug more powerful (increasing side effects), less powerful (reducing effectiveness), or create new effects that neither drug causes alone.

Drug interactions are one of the most common and preventable causes of medication-related harm. Understanding them is an important part of staying safe on medication.

Step 1: Know what you're taking

Write down every medication you take, including:

• Prescription medicines (tablets, inhalers, patches, injections)
• Over-the-counter medicines (painkillers, antihistamines, antacids)
• Vitamins and supplements
• Herbal products (St John's Wort is a notorious interactor)

Step 2: Check specific combinations

Use 247CanITakeWith to check any pair of items from your list. Pay particular attention to:

• New prescriptions combined with existing medication
• Over-the-counter painkillers combined with your regular medication
• Alcohol combined with any medication you take regularly

Step 3: Use your pharmacist

Your pharmacist is the most accessible and underused resource for medication safety. They can:

• Review your full medication list for interactions
• Advise on safe over-the-counter alternatives
• Identify interactions a website might miss

Ask for a "medication review" — NHS pharmacists offer this for free.

Red flags that need urgent attention

Contact your GP or pharmacist immediately if you experience any of the following after taking two medications together:

• Unusual bleeding or bruising
• Rapid or irregular heartbeat
• Sudden confusion or drowsiness
• Severe stomach pain
• Difficulty breathing
• Muscle pain or weakness

Common high-risk combinations

These are some of the most frequently encountered dangerous combinations:

• Sertraline + Tramadol — serotonin syndrome risk
• Warfarin + Ibuprofen — serious bleeding risk
• Metronidazole + Alcohol — severe disulfiram-like reaction
• Codeine + Diazepam — respiratory depression
• Diazepam + Alcohol — potentially fatal CNS depression