Contraindications

L-thyroxine must not be used if the thyroid gland is overactive. In addition, the drug should not be taken if the following diseases cannot be excluded: When treating post-menopausal women who have an increased risk of osteoporosis and suffer from hypothyroidism, the thyroid gland should be checked regularly to prevent elevated levels of L-thyroxine in the blood.

Diseases of the coronary vessels (e.g. angina pectoris)
High blood pressure
Weakness of the pituitary gland (pituitary insufficiency) or the adrenal cortex (adrenal cortex insufficiency)
Acute heart attack
Heart muscle inflammation (myocarditis)
Heart rhythm disturbances (tachyarrhythmias)

L-thyroxine must not be taken if high blood pressure is present and untreated.

The reason for this is that L-thyroxine has the effect of increasing the body’s drive and willingness to be active. This effect is also accompanied by an increase in blood pressure. This is very dangerous if high blood pressure exists.

Consequently, before starting to take L-thyroxine, the blood pressure should be checked. In this way, existing high blood pressure can be detected and treated if necessary. Once this is done, L-thyroxine may be taken.

L-thyroxine reduces the effect of blood sugar lowering drugs (antidiabetics). For this reason, the blood sugar level should be checked regularly, especially at the beginning of thyroid hormone therapy in diabetic patients. If necessary, the dose of the blood sugar-lowering medication must be adjusted.

L-thyroxine can enhance the effect of certain anticoagulants (coumarin derivatives). It is therefore recommended to have the blood coagulation values checked regularly under therapy with L-thyroxine. Barbiturates (certain sleeping pills) and certain other drugs can accelerate the breakdown of L-thyroxine by the liver and thus cause a reduced effect of L-thyroxine.

During pregnancy in patients with hypothyroidism, the need for L-thyroxine may be increased by the increased blood levels of female sex hormones (especially estrogen). Thyroid function should therefore be monitored both during and after pregnancy and the dose of thyroid hormone adjusted as necessary. It is strongly discouraged to take L-thyroxine and medication for hyperthyroidism (thyrostatic drugs) at the same time, as this requires a higher amount of thyrostatic drugs.

Thyrostatics are able (unlike L-thyroxine) to enter the child’s circulation via the placenta and can cause hypothyroidism in the child. As with many medications, there may also be interactions between L-thyroxine and the pill. Pills that contain estrogens as the active ingredient are particularly affected.

They can reduce the effect of L-thyroxine. For this reason the dosage of L-thyroxine must be discussed with your doctor when you take the pill for the first time or when you stop taking it, and it must be checked and adjusted if necessary. On the other hand, it is not known that L-thyroxine influences the effect of the pill. For this reason, contraceptive protection is still given if the pill is taken at the same time.