Information leaflet about the treatment of
thyrotoxicosis using radioiodine
This leaflet provides information about using radioiodine to
treat thyrotoxicosis. It explains how this treatment is given
and the safety precautions you need to follow after the
treatment. It also answers some of the most common
questions people ask about this treatment. If any of the
information is not clear or if you have questions not
answered by this leaflet, then please ring the Department of
Nuclear Medicine on 02920 316237.
What is thyrotoxicosis?
Thyrotoxicosis occurs when the thyroid gland produces too
much thyroid hormone.
What is radioiodine treatment?
Radioiodine treatment uses a form of iodine that is
radioactive. The iodine is taken up by the thyroid gland and
the radioactivity 'slows down' the thyroid's production of
Why has radioiodine treatment been suggested?
Your doctor will have explained that there are different types
of treatment for thyrotoxicosis. Radioiodine has been
suggested as a suitable treatment for you.
Where else in my body will the radioiodine go?
Most of the radioiodine will go to your thyroid. The rest will
pass from your body in your urine.
How will the radioiodine be given?
The radioiodine is normally given in the form of a capsule. If
you cannot swallow capsules, then it may be possible to
arrange for you to have the radioiodine in the form of a small
Will I feel ill afterwards?
No, you should feel no immediate after-effects except
possibly a slightly sore throat.
What about my tablets?
If your tablets are for controlling your thyrotoxicosis, then
you may need to stop these for some time. You will be told
how long to stop them for by your hospital doctor during
your clinic visit or in your appointment letter before your
treatment. Otherwise there should be no need to stop any
Can I have the treatment if I am pregnant?
Your doctor is the best person to advise you on this.
Generally pregnant women will only receive radioiodine if
the doctor who requests this treatment considers that this is
in your best interests.
Are there any risks in having children afterwards?
50 years experience of using radioiodine has shown no
effect on the health of children of patients who have had this
treatment. However, you should avoid pregnancy for at
least four months (but ideally six months to allow adequate
clinical follow up) after radioiodine treatment. You will be
asked to stop breast-feeding if you are doing so. Male
patients will be asked to avoid fathering children for four
months after radioiodine treatment.
How long before I can return to work?
You will probably need to take some time off work. This will
depend on the amount of radioiodine you receive and,
possibly, on the type of work you do.
For example if you are working with children or pregnant
women you may need to be off work longer. If your work
involves the use of photographic film again you may need
more time off.
You will be advised of the actual time you need to take off
work. This will either be during your hospital clinic visit or
when you are in the Nuclear Medicine Department.
Here is a rough guide to the time off work you may need:
• If you work on your own and do not come into long
periods of close contact with other members of the
public you can return to work immediately. This means
that you do not normally work within six feet of anyone
else for longer than one hour.
• If you work with other adults, none of whom could be
pregnant, then you can return to work after between
11 and 16 days.
• If you work with other adults, one or more of whom
could be pregnant or if you work with children then you
can return to work after 21 to 27 days.
• If your work does not fit in with any of the above, or
you feel your situation is not clear, then please ring the
Nuclear Medicine Department at Velindre Hospital for
further advice. The telephone number is on page 7.
Will there be any danger to my family or other people?
No, but you will be told to follow some simple rules to
reduce the risks to them. The length of time you will have to
follow these rules depends on the amount of radioiodine
your hospital doctor has prescribed. The exact length of
time will be discussed with you before you receive your
What are these precautions likely to be?
You will be advised to:
i) Avoid using public transport for journeys longer than
ii) Avoid going to places of public entertainment (for
example a cinema or restaurant)
iii) Avoid sharing a bed with your partner
iv) Use your own cutlery and dishes and wash them
v) Flush the toilet twice after use
These precautions usually apply for between 11 and 16
days. Again you will be advised about this.
You will also be asked to avoid prolonged close contact with
children and pregnant women for between 21 and 27 days.
Will I need to see a doctor after my radioiodine
Yes, you will see either the doctor who saw you in hospital
or your GP. You will need a blood test to check the effect of
the treatment on your thyroid.
How many radioiodine treatments will I need?
Usually, one treatment is enough. Sometimes however two
or three treatments are needed. The blood tests will help
decide exactly how many you need.
Are there any long-term side effects?
No, except that your thyroid gland may become under-
active. This could happen within a few weeks or many years
after treatment. The blood tests which check your thyroid
will pick this up.
What happens if my thyroid does become under-active?
You will be given tablets called 'Thyroxine' which usually
have no side effects.
If you have any other questions, please ask when you come
to the hospital. We want you to understand what the
For further information, please contact the Nuclear Medicine
029 2031 6237
029 2031 6236
Velindre Cancer Centre
Velindre Road, Whitchurch, Cardiff, CF14 2TL
This leaflet was written by health professionals. The
information contained in this leaflet is evidence based. It is
reviewed and updated every 2 years.
Prepared March 2004
Reviewed August 2010