Can You Take Different Medicines Together? Understanding Drug Interactions

Taking more than one medicine is common. You may have a prescription medicine for a long-term condition, an over-the-counter painkiller for a headache, or a supplement that you take every morning. The fact that each product is safe when used on its own does not automatically mean that every combination is suitable.

Some medicines can change the way another medicine works. Others can increase the likelihood of side effects or make an existing medicine less effective. These effects are known as drug interactions.

This does not mean that taking more than one medicine is inherently dangerous. Many people need several medicines as part of their treatment. The important point is to make sure that the combination is appropriate for you.

What is a drug interaction?

A drug interaction occurs when one medicine, substance or product affects the way another medicine works.

An interaction can have several effects. One medicine may increase the concentration of another in the body, potentially increasing its effects or side effects. Another medicine may reduce how much of the first medicine is absorbed or how quickly it is broken down.

Some combinations can also produce similar effects. For example, taking two medicines that can both cause drowsiness may make this side effect more pronounced.

Interactions are not limited to prescription medicines. They can involve:

• Prescription medicines
• Over-the-counter medicines
• Painkillers
• Vitamins and supplements
• Herbal remedies
• Medicines bought online
• Alcohol and certain foods

This is why healthcare professionals need to know about everything you are taking, not just medicines prescribed by your GP.

Can you take two medicines at the same time?

Sometimes you can. Sometimes you cannot.

There is no general rule that says two medicines must always be taken separately. Some medicines are routinely prescribed together because they work safely as part of the same treatment plan.

However, certain combinations should be avoided, while others may require a different dose, additional monitoring or specific instructions about when the medicines should be taken.

The safest approach is to check before adding a new medicine to your existing treatment.

This is particularly important if you are buying an over-the-counter medicine yourself. A product may appear unrelated to your regular prescription, but its active ingredients can still affect your treatment.

If you are unsure about the amount of medicine you should take, our guide to why medication dosages matter explains why doses are individual rather than interchangeable.

Why do medicines interact with each other?

There are several ways an interaction can happen.

One medicine can increase the effect of another

If two medicines have similar effects, taking them together can sometimes make those effects stronger.

For example, several medicines can cause drowsiness. Combining them may result in greater sleepiness than expected, which can affect concentration and coordination.

One medicine can reduce the effect of another

Some medicines interfere with the way another medicine is absorbed or processed by the body. This can reduce its effectiveness.

That can be particularly important when a medicine needs to maintain a consistent level in the body to work properly.

One medicine can increase the risk of side effects

A combination may make a particular side effect more likely or more severe.

For example, some medicines can increase the risk of bleeding when used alongside other medicines that affect blood clotting. The patient information leaflet for ibuprofen specifically warns about interactions with medicines such as anticoagulants and other NSAIDs.

The interaction can depend on the person

An interaction is not necessarily the same for everyone.

Age, other medicines, existing health conditions and how the body processes medicines can all affect the risk. This is one reason why medication combinations should be assessed in the context of the individual rather than based on a simple online list.

Common examples of medicine interactions

There are many possible interactions, and the examples below are intended to show why checking medicines is important rather than provide a complete list.

Painkillers and other medicines

Painkillers are particularly relevant because many are available without a prescription.

For example, ibuprofen belongs to a group of medicines called non-steroidal anti-inflammatory drugs (NSAIDs). Taking ibuprofen alongside another NSAID can increase the risk of gastrointestinal ulcers and bleeding. Certain medicines used to prevent blood clots can also interact with ibuprofen.

Paracetamol also needs to be used carefully. Some combination products contain paracetamol as one of their active ingredients, meaning that taking more than one product could unintentionally increase the total amount taken. The patient information leaflet for paracetamol advises checking with a pharmacist before taking other medicines containing paracetamol.

This is one reason it is important to check the active ingredients rather than relying only on the brand name.

Blood-thinning medicines

Medicines used to prevent blood clots can interact with other treatments.

For example, the patient information for clopidogrel highlights medicines that can increase bleeding risk, including anticoagulants, some NSAIDs and certain antidepressants.

Apixaban, another medicine used to prevent blood clots, can also be affected by other medicines, with some combinations increasing its effects and therefore the risk of bleeding.

Anyone taking an anticoagulant or antiplatelet medicine should therefore check with a healthcare professional before starting a new medicine.

Medicines for depression and other conditions

Some medicines that affect serotonin can interact with other treatments that influence the same system.

For example, the patient information for certain medicines warns about the possibility of serotonin syndrome when they are combined with particular antidepressants or other medicines affecting serotonin.

This does not mean that these medicines can never be used together. In some circumstances, a healthcare professional may deliberately prescribe combinations with appropriate precautions. The important point is that the combination should be assessed rather than assumed to be safe.

Do over-the-counter medicines interact with prescription medicines?

Yes.

This is one of the easiest things to overlook because over-the-counter medicines can seem less significant than prescription treatments.

A person may already take several prescribed medicines and then purchase a painkiller, cold remedy, antihistamine or other product without considering whether it could affect their existing treatment.

Some over-the-counter products also contain several active ingredients. A cold and flu medicine, for example, may contain a painkiller alongside other ingredients. Taking it alongside another product containing the same painkiller could result in taking more of that medicine than intended.

If you take regular prescription medicines, tell the pharmacist what you are already taking before buying an additional treatment. NHS guidance also recommends checking with a GP or pharmacist before starting new medicines, including those purchased without a prescription.

What about vitamins, supplements and herbal remedies?

Supplements should not automatically be treated as separate from medicines.

Vitamins, herbal remedies and other supplements can affect the way prescription medicines work. This is particularly important because people do not always mention supplements when discussing their medicines with a doctor or pharmacist.

We have previously covered this subject in more detail in The Hidden Risks of Mixing Supplements with Prescription Medication.

If you have started taking a supplement since your last prescription, make sure your pharmacist or doctor knows about it.

Does taking medicines at different times prevent interactions?

Not necessarily.

Spacing medicines apart can be part of the instructions for some treatments, but simply leaving an hour or two between medicines does not automatically prevent an interaction.

Some interactions occur because one medicine changes how another is absorbed. Others happen because medicines affect the same processes within the body and can therefore interact even when they are taken at different times.

This means you should not assume that a potentially unsuitable combination becomes safe simply because the doses are separated.

Always follow the specific instructions supplied with your medicine.

How can you check whether your medicines are safe together?

There are several sensible steps you can take.

1. Keep a list of everything you take

Include:

• Prescription medicines
• Over-the-counter medicines
• Vitamins
• Supplements
• Herbal remedies
• Medicines you take occasionally

Keeping an up-to-date list makes it much easier for a pharmacist or doctor to identify potential problems.

2. Read the patient information leaflet

The leaflet supplied with your medicine contains important information about other medicines and substances that may affect its use.

It can also explain what to do if you experience certain side effects or accidentally take too much.

Our guide on how to read a medication label without confusion provides further guidance on finding important information about a medicine.

3. Ask a pharmacist before starting something new

A pharmacist can help you understand whether a new medicine is suitable alongside your existing treatment.

This is particularly useful when you are considering an over-the-counter medicine and already take prescription medication.

4. Check the active ingredients

Do not rely solely on the product name.

Different brands can contain the same active ingredient. Checking the ingredients can help prevent accidental duplication, particularly with painkillers and cold or flu remedies.

5. Keep your medicines in their original packaging

Original packaging keeps important information together, including the medicine name, strength, expiry information and instructions.

It can also make it easier for a healthcare professional to identify exactly what you have taken.

For further advice, see our guide to how to store medicines safely at home.

What if you have accidentally taken two medicines together?

Do not automatically assume that something serious has happened, but do not ignore the situation either.

The risk depends on exactly which medicines were taken, the amount, when they were taken and the person taking them.

Check the packaging and patient information leaflet, then speak to a pharmacist, GP or other appropriate healthcare professional for advice.

If you have taken too much medicine, or you develop symptoms such as difficulty breathing, severe swelling, loss of consciousness, a seizure or another serious reaction, seek urgent medical attention.

Do not take an additional dose simply because you are uncertain about what happened. If you have missed a dose, our guide to what happens if you miss a dose explains why the correct response depends on the specific medicine.

What symptoms could indicate a problem?

An interaction does not always cause obvious symptoms. In some cases, the main concern is that one medicine has become less effective.

However, certain symptoms require prompt attention.

Seek urgent medical help if you experience symptoms such as:

• Difficulty breathing
• Swelling of the lips, mouth, tongue or throat
• Severe or rapidly developing rash
• Loss of consciousness
• Seizures
• Severe confusion
• Significant or unexplained bleeding

Serious allergic reactions can require immediate treatment. NHS guidance advises seeking urgent help for symptoms such as swelling of the face, lips or throat, difficulty breathing, or a rash following a medicine.

If you develop an unexpected or concerning symptom after starting a medicine, speak to a healthcare professional rather than trying to determine the cause yourself.

Who should be particularly careful about medicine interactions?

Anyone taking more than one medicine should check for interactions, but additional care may be appropriate for people who:

• Take several prescription medicines
• Have recently started a new medicine
• Regularly use over-the-counter medicines
• Take vitamins or herbal supplements
• Have long-term health conditions
• Have recently been discharged from hospital
• Have had changes to their medication
• Are unsure which medicines they are currently taking

People taking several medicines may benefit from a medication review. NHS England describes structured medication reviews as a way of considering a person’s medicines alongside their wider health, including whether combinations are causing or could cause harm.

What information should you give your pharmacist or doctor?

The more complete the information, the easier it is to assess your medicines properly.

When discussing a new medicine, tell the healthcare professional:

• The name of every medicine you take
• The strength of each medicine
• How often you take it
• Any medicines you take only occasionally
• Any vitamins or supplements
• Any herbal remedies
• Any known allergies
• Any significant changes to your medication recently

It is also useful to mention medicines that you have recently stopped taking, as some medicines can continue to affect the body after the final dose.

Do not stop a prescription medicine because of a possible interaction

Finding out that two medicines can interact does not necessarily mean that you should stop one of them.

Some combinations are intentionally prescribed together and monitored by healthcare professionals.

Stopping a prescribed medicine without advice can create its own risks. If you are concerned about a combination, speak to the prescriber or pharmacist before changing the dose or stopping treatment.

If your medicines have recently changed, it is also worth keeping the information together so that you know exactly which treatment you are currently taking.

How online pharmacy services can help

Online pharmacy services can make accessing medicines more convenient, but convenience should not replace appropriate checks.

A legitimate online pharmacy should have appropriate processes for assessing whether a medicine is suitable before supplying it where a prescription or clinical assessment is required.

Patients should also provide accurate information about their existing medicines and health circumstances. Leaving out a medicine because it is available without a prescription, or because it is only taken occasionally, can make it harder to identify potential interactions.

The same principle applies whether a medicine is obtained from an online pharmacy, community pharmacy, GP or hospital: healthcare professionals need an accurate picture of the medicines being taken.

The bottom line

Taking more than one medicine is not automatically unsafe. Many treatments are designed to be used together.

The important question is whether the particular combination is appropriate for the individual taking it.

Prescription medicines, over-the-counter treatments, supplements and herbal products can all be relevant when checking for interactions. Some combinations can increase side effects, reduce effectiveness or create more serious risks.

The safest approach is straightforward: keep an accurate list of your medicines, read the information supplied with them, check active ingredients and ask a pharmacist or doctor before adding a new treatment. If you are unsure whether two medicines can be taken together, do not guess. Getting professional advice before taking the combination can help prevent avoidable medication problems.