HRT & Hormone Contraceptive Pill and Thyroxine

Written by Dr Wendy Jones, MBE BSc, MSc, PhD, MRPharmSit.

This month’s blog on taking HRT, the contraceptive Pill and thyroxine has been kindly written for The Thyroid Trust by Dr Wendy Jones, MBE BSc, MSc, PhD, MRPharmS.  Wendy has been a community pharmacist for over 40 years, worked as a practice support pharmacist for the NHS, was a founding member of the Breastfeeding Network and is a published author. www.breastfeeding-and-medication.co.uk

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Can you take birth control with thyroid problems?

You can still take birth control if you have thyroid problems. However, your healthcare provider may take the opportunity to monitor your thyroid function to check for any changes around 6 weeks after you commence the birth control pills.
In a study Qiu et al  (2021) demonstrated a significant association between history of taking birth control pills for more than 10 years and hypothyroidism.
Google searches suggest that thyroid medication and oral contraception should not be taken simultaneously suggesting a 4 hour window between the two drugs  but I have been unable to trace any reference source that confirms this. 

Thyroid and the menopause
In the same way it is suggested that oestrogen in HRT can affect thyroid management. 

Menopausal diagnosis can be problematic as every woman tends to experience slightly differently. Women with pre-existing hypothyroidism treated with thyroxine may require an increase in their thyroxine dose after starting HRT. It is useful for thyroid function tests to be re-checked around 6 weeks after starting HRT.

Soya and thyroid 
There is also evidence to suggest that soy foods may inhibit the absorption of thyroxine and increase the dose of thyroid hormone required by hypothyroid patients. Generally, it's best to wait four hours after taking thyroid medication to consume any products that contain soy. The same guidelines apply to other products that may impair the body's ability to absorb thyroid medication, including concentrated iron and calcium supplements, and antacids that contain calcium or aluminium hydroxide (Messina 2006).

References
● Qiu Y, Hu Y, Xing Z, et alBirth control pills and risk of hypothyroidism: a cross-sectional study of the National Health and Nutrition Examination Survey, 2007–2012BMJ Open 2021;11:e046607

● Messina M, Redmond G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid. 2006 Mar;16(3):249-58. doi: 10.1089/thy.2006.16.249. PMID: 16571087.