While you can take levothyroxine at night, it generally is not recommended. Morning doses are recommended to ensure consistent dosing and drug levels.
Levothyroxine is considered a narrow therapeutic index drug, meaning small changes in dose can result in large differences in drug efficacy. Levothyroxine is dosed in micrograms, not milligrams, giving you an idea of how small these doses are. Even a small difference in the absorption of the drug can make a big difference.
To ensure consistent dosing, it is recommended to take levothyoxine on an empty stomach, 30 minutes before eating, with a full glass of water in the morning. The reason why this is important is because food and other medications can decrease the absorption of levothyroxine in your stomach, which could lead to your thyroid hormone levels being low.
In addition to food, many medications that can decrease the absorption of levothyroxine including calcium carbonate, iron supplements, sucralfate, antacids, cholestyramine, colestipol, and sodium polystyrene sulfonate.
If you take levothyorxine inconsistently, there is a high chance that drug levels will fluctuate. This could theoretically result in changing thyroid blood levels, which may cause symptoms of hypothyroidism. Symptoms of hypothyroidism include:
- Feeling cold
- Weight gain
- Poor memory
- Hair loss
- Lower than normal pulse rate
Due to the need for consistent dosing, morning is often seen as the best time to dose. If you take the drug in the evening, you may have undigested food that could affect absorption. In addition, several other factors can affect your metabolism, theoretically altering drug absorption when you take it later in the day (e.g. stress and your daily activity levels).
Taking the medication first thing in the morning typically is the best way to ensure consistent dosing. If you are interested in changing the timing of your dose, you should talk to your doctor first and make them aware. It certainly is possible to dose in the evening, you just need to be careful to try to take the medication at the same time and under the same conditions.