How the treatments make you feel sick or vomit is actually quite complicated. Nausea and vomiting are controlled by a part of the brain known as the ‘vomiting centre’. There are different ways that this vomiting centre can be ‘triggered’. The nerves in the gut/stomach can be stimulated by something, like drugs or radiotherapy, and ‘tell’ the vomiting centre that you want to be sick. Or it could be that the drugs or radiotherapy are affecting other parts of the brain, not the vomiting centre itself, which then ‘tells’ the vomiting centre that you are feeling sick or to actually vomit.
- chemotherapy (anti-cancer drugs) - some types of chemo, but not all, can affect the vomiting centre and cause you to feel or be sick.
- radiotherapy (high energy x-ray treatment) to the brain, stomach or bowel area can cause sickness because it can affect the vomiting centre in the brain or the nerves in the digestive system.
- morphine-based medicines (such as painkillers) can cause sickness by upsetting the delicate chemical balance in the bloodstream.
other reasons you might feel sick when you have cancer
There are also physical reasons just because of the cancer itself that can cause sickness…
- changes in the chemistry of the body such as high levels of calcium in the blood, or raised pressure within the brain, can affect the vomiting centre. These changes can happen for a number of different reasons, as different cancers affect the body differently.
- damage to the liver - if the liver isn’t working properly, waste products can build up in the blood and cause sickness.
- blockage of the bowel can be caused by cancers that affect the tummy or the pelvis.
- severe constipation can block the bowel.
psychological or emotional reasons can cause sickness…
- anxiety - feeling anxious and worried about the cancer or your treatment may cause or add to your sickness.
- anticipatory nausea - feelings of nausea and sometimes vomiting can be triggered by things that remind you of previous experiences of being sick. For example, people who get travel sick can feel a wave of nausea just sitting in a car, even though it’s not moving. This can sometimes occur with chemo, so that if you’ve had sickness with one lot of treatment, you might feel sick before the next lot. And some people find that they feel sick just going into the hospital. Tell your doctors if this is happening for you and they may give you some extra medication that can help.
