Taking medicines | Cancer Research UK
Cancer Research UK on Google+ Cancer Research UK on Facebook Cancer Research UK on Twitter

Taking medicines

Find out about taking medicines safely and why you must follow the instructions about how to take them. There is information about


Why you must follow instructions about taking medicines

Taking medicines at home is a common part of cancer treatment. The medicines are much more likely to work if you take them as instructed. But we know from research that many people don’t take them as they should. There are a number of reasons why people may not take medicines as they are prescribed.

By the time a medicine is ready to be licensed, we know the dose and how you should take it. How you take a drug by mouth can affect how much of it is absorbed into your body. So if you don’t take it as you should, less of the drug may reach your cancer.

There are a number of factors that affect how a drug is absorbed and how well it works.


Things that affect how medicines work

There are a number of things that can affect how well a drug works.

Taking medicines at the correct times

Drugs stay active in the body for a particular length of time. This may be a couple of hours or longer than a day. This is why you need to take different drugs at different intervals of time. How long it takes the body to absorb a drug and reach the level at which it works best also varies. 

You need to take most drugs at regular times to make sure you have the right level of the drug in your body. If you forget or miss a dose it can take some time to get back to the right level. This is the same for drugs that control symptoms or that treat your cancer. For example, painkillers work best if you take them regularly and maintain a level of the drug that keeps pain under control. In the same way, you need to maintain cancer drug levels that allow them to act on cancer cells.

Taking the medicine for the correct length of time

It is also important to keep taking a drug for as long as your doctor has told you to. This might be weeks, months or even years. For example, the hormone therapy tamoxifen for breast cancer is a tablet you take daily for 5 years. It reduces the risk of the cancer coming back. The 5 year period was chosen after a lot of clinical research comparing how well the drug worked when taken for different numbers of years. The time that worked best at stopping the breast cancer returning was 5 years. A shorter time meant the cancer was more likely to come back. A longer time didn’t significantly help to lower the risk any further.

You take some cancer medicines in treatment cycles. This means that you take the drug for a set period of time, followed by a break, also for a fixed period of time. So, you might take a drug every day for a week and then not take it for 2 weeks. This 3 week period in total is one cycle of treatment. It is important to remember to take the cancer medicines exactly as you have been told to. The break from treatment is important too. For many cancer drugs, it allows your body to recover.

Don't forget to take them

We all forget to take medicines sometimes. It can help to write down when you need to take them, along with any instructions you need to follow. If you have several different tablets to take, a pill box can be helpful. These are divided into smaller boxes for each day of the week. There are compartments for different times of the day. 

You fill the box up once a week with your tablets. Or you can get someone to do it for you.

Eating and drinking

For drugs to work, including cancer drugs, they must be broken down and absorbed into the body. When you take medicines by mouth as tablets, capsules or liquids, this process happens in the stomach or gut.

Some drugs are better absorbed on a full stomach and some on an empty stomach. If there are particular instructions about this your doctor, nurse or pharmacist will tell you. And it will be on the information sheet you get with your tablets.

Some foods affect how much of a drug you absorb and might increase or decrease it. This can affect how the drug works, making it stronger or weaker. For example, grapefruit interferes with a number of drugs. If you are taking one of those drugs you should not eat grapefruit or drink grapefruit juice at all.

If we know that a particular food or drink is likely to affect the medicine you are taking, this will be part of the instructions you get with your drugs. If you are not sure if you should take your drugs on an empty stomach or not, check with your doctor, nurse or pharmacist.

Stomach upsets

If you have diarrhoea or are being sick it might affect the amount of the drug in your body. With diarrhoea, any drugs you are taking are likely to move through your gut much faster than normal. Then you may not absorb them as much as usual. If you are being sick, you may bring up your last dose.

Tell your cancer doctor or nurse if you have diarrhoea or are being sick. They will be able to prescribe medicines to help. And they need to know how your cancer treatment is being affected.

Interactions with other medicines

Some drugs can affect each other, changing how much you absorb. Tell your doctor about any other medicines you are taking, including vitamins, and alternative or complementary therapies. These supplements or therapies can also interfere with how well medicines work. A commonly quoted example is St John’s Wort, which can affect the absorption of drugs.

Medicines you buy yourself can interfere with prescribed medicines. For example laxatives will make a drug pass through your system more quickly, and will affect how you absorb it. You need to check with your cancer doctor, nurse or pharmacist before you take any medicines that you have bought yourself.

Storage and expiry dates

Like food, some drugs can go off. So it is important to follow any instructions about where and how you keep them. Some need to be kept in the fridge. Others need to be kept at room temperature. Many of us tend to keep them in the bathroom cabinet. But because the temperature varies a lot in bathrooms and the air may be damp, it is best not to keep medicines there.

All medicines have expiry dates. Make sure your medicines are within the expiry date. This includes any medicines that you have bought yourself as they may have been in your cupboard for a while.


Why people don’t take medicines correctly

There are many reasons why people don’t take medicines as they’ve been told to.

We know from research that people sometimes don’t understand exactly how to take medicines, or what it will mean if they don’t take them. If you don’t understand why you are taking a particular medicine you are less likely to carry on taking it.

We also know from research that sometimes people haven’t been told how to take medicines, or the instructions were too complicated. If you don’t understand, you can ask your doctor, nurse or pharmacist to explain again. It might help to ask them to write it down.

Sometimes, there are practical reasons why people don’t take medicines. Some people have difficulty swallowing tablets, or they might be unable to open the bottle. If these are problems for you, tell your doctor, nurse or pharmacist. Some drugs are available as liquids or you can have them in a different type of container.

Side effects of a drug may be too difficult to cope with, or the medicine may taste horrible. Side effects can often be controlled so let your doctor or nurse know if you have them. Your doctor or nurse can look at ways of helping you cope with any problems.

Ideally, we would all remember to take our medicines exactly as we should. But everyone forgets to take tablets sometimes. What you need to do if you forget a dose depends on the medicine you are taking. Missing one dose is unlikely to be a problem. But missing a dose a couple of times a day, or in a week for a daily tablet, could mean the treatment doesn’t work as well as it should. If you have missed several doses in a row, do tell your cancer doctor or specialist nurse.


What you can do

There are a number of things you can do to make sure you are taking your medicines as you should.

Find out why you are taking each drug. If you know what it’s for and how important it is, that will help you to remember.

Make sure you know how you should take each drug including

  • What time to take it
  • Whether you can take it at the same time as other drugs
  • When to stop taking the drug
  • Whether you need to take it with a full or empty stomach

Setting an alarm

You might find that setting an alarm on your watch, clock or mobile phone can help, particularly if you are only taking a tablet once a day. If you are taking more than that, you could make a chart with all your drugs and times listed. You could ask a helpful friend or relative to make one for you if you find it a bit daunting. 

Making a chart

You can make a write on / wipe off chart if you cover it in clear plastic film. Then you can tick off the medicines as you take them. Sometimes people forget whether they have taken a drug or not, so a chart can help with that too.

Finding out about your medicines

You need to know for each drug

  • How should you store it
  • How long will you be taking it for
  • What the side effects are and who you can contact if you have any
  • What to do if you miss a dose

Write this information down or ask the doctor, nurse, or pharmacist to write it down. It can be very easy to forget, especially if you are taking a number of different drugs.

Rate this page:
Submit rating


Rated 5 out of 5 based on 22 votes
Rate this page
Rate this page for no comments box
Please enter feedback to continue submitting
Send feedback
Question about cancer? Contact our information nurse team

No Error

Updated: 13 April 2016