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| Is it dangerous to take different medicines at the same time? |
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Reviewed by Dr Christine Clark, pharmacist
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What is
drug interaction?
Drug interactions can occur
when people take two or more different medicines at the same
time.
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| Make sure you always know what medicines
you are taking and why. |
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The medicines might be taken for the same
illness, such as quinsy (an abscess in the throat), for
which a person needs antibiotics and painkillers. Or it
may be because they suffer from two different diseases at
the same time, such as gastric ulcers and arthritis, for which they need
acid neutralisers and medicines for arthritis.
Medicines can sometimes influence each other inside the body, producing an
increased effect, extra side effects, or decreased
effectiveness of one or more drugs. This is called a drug
interaction.
How can two different drugs
influence each other's effect?
Nearly all medicines are broken down by specific
enzymes in the liver, and then excreted as smaller
molecules through the kidneys. Some medicines can affect the way other medicines are broken down in the liver, or are filtered into the urine by the kidneys.
If
medicine A inhibits the enzyme responsible for breaking down
medicine B, the result can be an excessive amount of
medicine B in the bloodstream. This can increase the
chance of serious side effects. If a doctor thinks that
both medicines are necessary at the same time, they will
ensure that the dose of medicine B is reduced, to avoid
any adverse effects.
If, on the
other hand, medicine A increases the activity of the enzyme
responsible for breaking down medicine B, the breakdown will
occur much faster and the effect of medicine B will be
decreased or lost. In that case, a doctor will increase
the dose of medicine B.
Medicines
can also influence each other in other ways; for instance,
they can affect absorption from the intestines or excretion by the kidneys. In both instances, this can result in
effects similar to those described above - too much or too
little medicine in the bloodstream, which may lead to
serious side effects or little or no effect at
all.
If medicines that can have similar side effects are taken together, there may also be a chance that the side effects will be additive. For example, if a sedating anthistamine is taken by someone who is also taking a strong painkiller that can cause drowsiness, for example morphine, then any drowsiness is likely to be increased.
Do I have to tell my doctor about all the medicines I
am using?
As long as a doctor or pharmacist has
taken into account the effect of taking two or more
medicines at the same time it should be perfectly safe.
For this reason you should always tell your doctor about all the medicines you
are using, including herbal remedies and those bought without a prescription, since drug interactions can occur with these too.
When buying
over-the-counter medicines from a chemist you should also
remember to check with the pharmacist whether the new medicine is safe to take with any other medicines you are
currently using.
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Based on a text by Unni
Elmer Jeppesen
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Last updated 28.03.2007
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