A recent article in Clinical Thyroidology for Patients described a study suggesting that the use of thyroid replacement hormone at night is as effective as a daytime dose. In addition, absorption was reported to be better with the nightly dose, primarily based on its ability to cause a lower TSH level. This, as I'll explain, would be expected from night-time dosing, making this presumption questionable.

The important take-away point from this article is that it's best to take replacement hormone at about the same time each day. Normally, the pituitary secretes its highest amounts of TSH at night when we're sleeping and the amount produced and secreted is dependent on the blood level of thyroid hormone. When the dose of replacement hormone is taken in the morning, the blood levels of FT4 and FT3 are lowest at night....although on steady dose of levothyroxine the levels of FT4 should be stable throughout the day after the initial peak. Throughout the morning TSH remains high and then begins its regular fall. Having enough TSH ensures that thyroid cells are stimulated to produce adequate hormone....or to the best of their ability.

In people on full replacement hormone, the TSH doesn't matter in this regard because thyroid cells aren't producing thyroid hormone. In patients with some thyroid function, a higher TSH allows their glands to produce more natural hormone. When the dose of replacement hormone is taken at night, the peak levels interfere with TSH production and defeat this purpose.

In his book on Hope and Healing, Dr. Neal Nathan describes the use of T3 replacement hormone and recommends that the dose be taken every 12 hours because of its short half life. Even then a dose taken at 8am and 8 pm allows T3 to peak and then start to fall before the usual rise in TSH, which is about 2AM.  Since we're all individuals with variable amounts of thyroid function and differences related to work schedule, diet, activity and drug absorption, deciding when to take our dose is more of an individual matter. Following the same dosing pattern each day appears to be the most important consideration.