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Why you shouldn’t exceed the recommended dose of a medicine

What are recommended doses?

  • At which dose is the drug most effective?
  • What is the lowest effective dose?
  • At what point are the dose limiting side-effects visible in the majority of people?

The answers to these questions provide what is known as the “therapeutic window” of each drug. That is the dose range of which the drug is both effective and relatively free of side effects.

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The diagram above shows what happens when a single dose of a medicine is taken. The curve represents the concentration of the drug in the blood. Unless the drug is taken in overdose its blood concentration will not rise to the point where side effects are very likely to occur. When taken at the recommended dose, for a period of time it stays in the range where the desired medicinal effects are delivered (the therapeutic window) – the pain relief is felt for an effective duration of time. Therefore, each medicine comes with a recommendation for the amount and how frequently it should be taken, to be at its peak of effect in the average person.

Why you should follow dosage instructions?

The balance of effectiveness versus side effects provides the basis for a recommended dose of a given medicine. There may also be different doses needed for older people or for children. More severe disorders may require a higher dose of the same drug. For example, a higher quantity of painkillers may be required to treat rheumatoid arthritis than is necessary to treat a tension headache.

In addition, most medication is also recommended to be used for a finite period of time. For headaches, it is recommended that you seek medical advice if you need to take painkillers for more than 10 days continuously.

It is equally important that you take the medicine often enough when applicable. Regularly missing doses may mean in some instances that insufficient medicine accumulates in the body which then may not deliver its full beneficial effect. If a product is designed to be taken four times a day, it means that the duration of the drug in the blood is probably quite short. Taking more of the drug twice a day instead, is unlikely to deliver the desired continuous medicinal effect.

What do you do if you take too much?

We outline a number of precautions that help to prevent accidental overdose or mistakes with a medicinal product:

  • Always read medication labels carefully and take all medications only as directed. Keep all medications in their original packaging, locked away in a safe secure place and out of reach and sight of children.
  • Take care when taking medicines of any kind. Whether you have been prescribed medication by a doctor or are using over-the-counter medicines always follow the instructions carefully. Never share medicines with others or use medication that is suited to a different illness or condition. If you notice any side effects, see your pharmacist or GP.
  • Do not stockpile unnecessary drugs. Return them to the pharmacist if you no longer need them.
  • Always inform your doctor or other health professional of a previous overdose.
  • Be cautious when taking different medicines or substances (including alcohol) together, as some medicines can interact with each other and increase the risk of adverse effects (your pharmacist or doctor should advise you on potential interactions).

However, if you believe that you have taken too much of a medicine, immediately contact your GP, or go to the accident and emergency department of your local hospital to assess the situation. There is also a national poisons telephone helpline in the UK that is part of the public health service, which can advise on cases where too much medicine may have been taken.1

If symptoms develop after taking too much of a medicine, it could be serious and will require immediate action. Accurate information will be needed - the specific name of the medicine, the amount consumed and the time when the medicine was taken. In most cases the medicine's packaging will identify the composition of the medicine and its dosage strength, so it is very useful to have this to hand.

To summarise, it is essential to be very careful with all medicines. ALWAYS follow the instructions given on the label, the prescription or by your doctor or pharmacist. Medicines also come with an information leaflet that states clearly what you should or should not do with the medicine. If you are ever in any doubt, even if you have followed all the instructions as directed, doctors and pharmacists are at hand to give you advice.

 

Data sources:
1. http://www.npis.org/telephone.html