Levothyroxine (T4)

Levothyroxine sodium is a drug approved by the FDA as an oral and injectable prescription thyroid hormone medication that is used to treat underactive thyroid (hypothyroidism) and other conditions. Hypothyroidism is a medical term that refers to any state in which a person’s thyroid hormone production is below normal.




Levothyroxine is the recommended form of thyroid hormone for routine treatment of primary hypothyroidism by the American Thyroid Association and the American Association of Clinical Endocrinologists, in part because of its efficacy in resolving the symptoms of hypothyroidism, favorable side-effect profile, ease of.

This medication replaces or provides thyroid hormone support, which is normally produced by the thyroid gland. Low thyroid hormone levels can occur naturally or when the thyroid gland is injured by radiation/medications or removed by surgery. Having enough thyroid hormone is important for maintaining normal mental health and physical activity. In children, having enough thyroid hormone is important for normal mental and physical development. Levothyroxine is also know as L-thyroxine.

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How it works?

Synthetic forms of the thyroid hormone T4 are generally called levothyroxine, and they are considered the standard treatment for hypothyroidism. Levothyroxine is considered a levoisomer, which simply means that the compound was produced by rotating at a specific wavelength but this has no impact on its biological function. As such, levothyroxine mimics the natural hormone. Though this hormone is man-made, synthetic T4 hormones are very similar to the T4 that is produced and released by the thyroid gland.

Side Effects

Common side effects associated with using levothyroxine include:
Chest pain (angina pectoris)
Joint pain
Congestive heart failure
Increased pulse
Heart attack
Irregular heartbeat
Choking sensation
Mood changes
Heat intolerance
Muscle weakness
Pseudomotor cerebri
Hair loss
Weight loss
Shortness of breath
Fast heart rate
Decreased bone mineral density

More information

Avoid under-treatment or over-treatment, which may result in adverse effects.

Use caution in cardiovascular disease, HTN, endocrine disorders, osteoporosis, or myxedema

Initiate lower dose in elderly, those with angina pectoris, cardiovascular disease, or in those with severe hypothyroidism.
Do NOT generally use levothyroxine sodium preparations interchangeably, due to narrow therapeutic index.
Check for bioequivalence if switching brands/generics.


1.7 mcg/kg or 100-125 mcg PO qDay; not to exceed 300 mcg/day
>50 years (or <50 yr with CV disease)
Usual initial drug dose: 25-50 mcg/day
May adjust drug dose by 12.5-25 mcg q6-8Week


T3 and T4 travel in your bloodstream to reach almost every cell in the body. The hormones regulate the speed with which the cells/metabolism work. For example, T3 and T4 regulate your heart rate and how fast your intestines process food. So if T3 and T4 levels are low, your heart rate may be slower than normal, and you may have constipation/weight gain. If T3 and T4 levels are high, you may have a rapid heart rate and diarrhea/weight loss.

User reviews

Review 1
I have been on several thyroid medications for 8 plus years. I was always tired fatigue, hair loss extreme weight gain. I started Tirosint and instantly I started feeling better.”

Review 2

I have been using Tirosint for over 8 months. I feel good and more energetic during my day. I can actually get more work done without having to take a mid day nap. However, I haven’t done blood work to see how the real effects are taking place within, but for the pass two months I starting experiencing terrible joint pains in my wrist, fingers and legs. So I’m starting to wonder base on some of the other comments if this med is cause these pains.

Review 3

Total-Thyroid ectomy following Graves substernal goiter 8 mo ago. On 175mg Levothyroxin. Felt good but as the months go by, a host of symptoms: intense moods/anger, depression, spinning thoughts; hair loss, brittle no curl dry; diminished eyesight, dry irritated; bone pain; hot poker nerve pain feet; muscle cramps; tendon disturbances; Charlie horses legs rib cage!! ; hot cold flashes; itchy skin; swollen itchy neck; diarrhea; joint pain swelling; and now shoulder blade hot poker pains. Insurance forced LevoT first….I want to switch. Would love to have recommendations. I’m 70 but have always felt pretty good until now. Supplements of calcium, D3 have helped some. Also taking zinc, magnesium and potassium – helping? hurting?

Review 4

Synthroid is terrible it fave me an exacerbation of mental health symptoms! Nervous, restless, anxiety, fatigue, constant dark thoughts and depression. My TSH dropped from .50 to .02 and still no symptoms of hyper just the same symptoms of hypo. Weight gain, tired, depression. I thought I was losing my mind! Trying to adjust psyche meds thinking that was the issue didn’t work cuz it was the levo causing the problem. It’s difficult to separate symptoms of mental health problems from thyroid problems because they can be similar. Got a referral from PCP to see an Endocrinologist. They switched me to Armour. Significant improvement. Levothyroxine stinks! I’d rather take no thyroid medication and suffer the consequences than take Levothyroxine.


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