Types of side effects
Dose-related effects
Most side effects are related to the amount of medicine taken. These are said to be ‘dose related’ because the number of side effects noted and the level of discomfort they cause increase as the dose of the medicine is increased. These types of side effects are quite common, but most are relatively mild.
Lowering the dose or increasing the time between doses will normally reduce or stop a dose-related side effect.
| Type of side effect | Description |
| Mild | Can usually be tolerated without the need to stop taking your medicine. |
| Moderate | You may need to lower the dose of your medicine and/or you may need to take another medicine that will help reduce or stop the side effect. |
| Serious | Can be life-threatening, but these are rare. With any serious side effect, your medicine must be stopped and you may need to receive treatment in hospital. |
Non-dose-related effects
Allergic and idiosyncratic (unexpected) side effects are not related to the amount of medicine taken.
Allergic reactions – occur because a patient is allergic or hypersensitive to a particular medicine. They do not usually occur upon the first use of the medicine, but following subsequent usage. Occasionally a patient is allergic to a substance used to produce the medicine (e.g. a preservative in the tablet) rather than to the active ingredient. If you know you have an allergy, ask your doctor or pharmacist for advice.
Idiosyncratic (unexpected) reactions – These occur unexpectedly and can occur on the first use of a medicine. They occur in only a very small number of people and the reason for them is unclear.
Non-dose-related side effects are largely unpredictable. They tend to be more severe than those that are dose related and can be serious in extreme cases. However, they are also far less common.
Medicine–medicine and medicine–food interactions
Some side effects can result from interactions with other medicines or even with food or drinks:
- Taking more than one medicine at a time can produce effects that are different to those which occur when either medicine is taken alone, or may make a particular side effect more noticeable. For example, taking more than one medicine that causes drowsiness may make you feel very drowsy, making it dangerous to drive.
- Medicines can also interact with food or drink. For example, some medicines used to lower cholesterol interact badly with grapefruit juice.
REMEMBER TO ASK YOUR DOCTOR OR PHARMACIST ABOUT ANY MEDICINES, FOODS OR DRINKS THAT YOU SHOULD AVOID WHILST TAKING YOUR MEDICINE.
