Introduction
Interactions between so-called 'natural therapies' and clinical medicines are an unquantified problem in the Australian community, due to a lack of awareness and reporting from consumers and health professionals alike.
The Queensland Medication Helpline is a direct link to consumers and their medication concerns. Over the past five years we have reported, to the Adverse Drug Reactions Advisory Committee, a variety of suspected adverse effects and interactions between clinical and herbal/nutritional medicines. An interesting example is the potential interaction between thyroxine and celery seed tablets.
Case reports
Our first case involved a 55-year-old woman who, after considerable monitoring, had finally been stabilised on a daily dose of thyroxine 100 microgram. A month later, her doctor found that her T4 levels were low again and her dose was doubled. The patient then remembered that in the past month she had also started taking celery seed tablets for osteoarthritis. Suspecting a potential interaction, she ceased the celery seed tablets without increasing the thyroxine dose as the doctor had advised. Next time her thyroxine levels were checked they had increased to within the normal range. She tried recommencing celery seed a month later but after a week she felt lethargic, bloated and had dry skin. When she stopped the celery seed tablets, she reported that her 'general energy levels improved'.
A second report was received from a 49-year-old woman who had taken thyroxine for many years. When her T4 became extremely low her doctor suspected that she had not been taking her tablets. The patient argued that she had taken her thyroxine, but she had recently commenced taking celery seed tablets to treat arthritis. She ceased the celery seed tablets and one month later her thyroxine levels had returned to within the normal range.
Evidence
Celery seed extracts (Apium graveolens) are a popular herbal remedy for the treatment of arthritis, gout, fluid retention and cystitis. Celery seed/fruit should not be confused with the edible celery stem.1 Studies have shown that celery plant extracts have anti-inflammatory activity against carrageenan-induced rat paw oedema.2 Hypotensive and hypoglycemic activities have also been reported.1 In preliminary research, five of 23 celery-based preparations showed antiarthritic effects, but no anti-inflammatory or antipyretic effects. The celery seed activity was thought to be dependent on processing at low temperatures.3
An extensive literature search did not find other reports of an interaction between celery seed extracts and thyroxine. However, when reference was made to these case studies in an article in a Queensland newspaper, the Queensland Medication Helpline received a flood of calls about similar experiences. A total of 10 cases are now on file. Although the validity of these anecdotal reports needs to be tested, as their number accumulates so too does the suspicion that the interaction is real. A pharmacokinetic study of the T4-celery interaction is under consideration by the Mater Hospital Pharmacy Services' Therapeutic Advisory Service.
Conclusion
Anecdotal evidence indicates a potential interaction between thyroxine and celery seed tablets. Since consumers often fail to volunteer details of self-medication with complementary medicines, prescribers and pharmacists should ask directly what herbal/nutritional medicines consumers are taking. If celery seed tablets are being co-administered with thyroxine, it is strongly recommended that thyroid function tests are closely monitored and any suspected interaction reported.
