Laxatives and levothyroxine, what precautions should you take?

Hypothyroidism is linked to a decrease in the secretion of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). This results in a slowdown in metabolism leading to non-specific symptoms such as asthenia, weight gain, muscle weakness or even depressive symptoms. Unusual and persistent constipation may also be observed. Levothyroxine (Levothyrox and generics) is the standard treatment for hypothyroidism. Typically, plasma thyroid hormone balance is not achieved for six weeks. Within this time frame, symptoms related to hypothyroidism such as constipation should be treated. For this, ballast or osmotic laxatives are preferred, but they are also responsible for a reduction in the absorption of other specialties taken orally. On the other hand, as levothyroxine is a drug with a narrow therapeutic window, drug interactions should be monitored. The patient must therefore be advised to take levothyroxine one hour before laxatives and following the usual methods: a single dose upon waking up, on an empty stomach, half an hour before breakfast. Hygiene and diet rules complement the management of constipation such as increasing fiber intake (fruits and vegetables, whole grains, etc.) and consuming mineral water enriched with magnesium.

Sources: High Health Authority; Swiss Medical Journal; public drug database.