Does Levothyroxine Cause Cancer? Study of Over 600,000 Thyroid Patients Explained

A new study of over 600,000 thyroid patients from Taiwan suggested that thyroid patients taking levothyroxine have a 50% increased risk of developing cancer at any site. While concerning, the results of this study certainly do not prove that levothyroxine causes cancer but every thyroid patient taking levothyroxine should be aware of this potential connection. https://onlinelibrary.wiley.com/doi/10.1111/cas.14908 This information is not meant to cause fear or alarm but to simply break down this study, explain some of the issues with the study, and some of the key takeaways. Let’s start with the problems first: #1. The study was retrospective. Retrospective studies look backward in time at existing data and can show a correlation between things but do not necessarily prove causation. This is very important because many thyroid patients suffer from conditions that can also increase cancer risk and these must be taken into account. #2. More research is still needed before any definitive conclusion is made. This is only one study and before any claim can be definitely made, there must be other studies that account for the issues listed above. #3. We don’t have information on other thyroid medications. This study only took into account levothyroxine and didn’t account for other thyroid medications that may be better for thyroid management such as NDT formulations. #4. Even though levothyroxine is synthetic, it is still bioidentical. The fact that levothyroxine is body identical or bioidentical is good because it means it’s less likely to result in cancer. Bioidentical hormones can impact cancer risk but typically only if they are dosed incorrectly (either too much or too little). Some key takeaways and lessons from this study include: #1. Don’t take thyroid medication unless you need it! I have many articles and videos which can help you determine if you are someone that may be able to get off of their thyroid medication. #2. It may be difficult for some thyroid patients to get thyroid medication fro