Comprehensive thyroid hormone replacement
Provides stable, long-acting thyroid hormone replacement therapy
T4 Levothyroxine - Primary Thyroid Hormone
The primary thyroid hormone and most commonly prescribed thyroid medication that serves as a prohormone for the active T3
Scientific nameLevothyroxine sodium (T4)
FormulaC15H11I4NO4
Molecular weight776.87 g/mol
CAS51-48-9
80
absorption score
6
safety / 10
50
USD per month
5
documented interactions
Check it against something
T4 Levothyroxine - Primary Thyroid Hormone with:
- Amylase
- Ashwagandha
- Avocado Oil
- BCAA (Branched-Chain Amino Acids)
- Beetroot Powder
- Beta-Alanine
- Bifidobacterium lactis
- Bifidobacterium longum
- Bovine Collagen
- Caffeine
- Calcium
- Calcium Bone Formula
- Calcium Carbonate
- Casein Protein
- Chicken Collagen
- Choline (Bitartrate)
- Chondroitin Sulfate
- Coconut Oil
- Collagen Peptides
- Comprehensive Immune Support Complex
- Comprehensive Multivitamin-Mineral Complex
- Creatine HCL
- Creatine Monohydrate
- D-Mannose
- DHA
- Electrolyte Blend
- EPA
- Fish Oil (EPA/DHA)
- Folate (5-MTHF)
- Ginger
- Iron Fumarate
- Iron Sulfate
- Joint Mobility Formula
- Keratin
- Krill Oil
- L-Carnitine
- L-Citrulline
- Lactase
- Lactobacillus acidophilus
- Lactobacillus rhamnosus
- Lipase
- Magnesium Citrate
- Magnesium Glycinate
- Magnesium Oxide
- Marine Collagen
- Melatonin
- Modafinil
- Olive Oil Extract
- Omega-3 + Curcumin + Vitamin D Triple Anti-Inflammatory Formula
- Papain
- Protease
- Saccharomyces boulardii
- Selenium (Thyroid Support)
- Turmeric
- Vitamin B12 (Cyanocobalamin)
- Vitamin B12 (Methylcobalamin)
- Vitamin C (Ascorbic Acid)
- Vitamin C (Sodium Ascorbate)
- Vitamin D3
- Whey Protein
- Zinc Gluconate
Nothing found
82
out of 100
Works better together
Compatible. Timing differs, so follow each supplement's own window.
What it does
mechanism and evidence for each claimImproved metabolism and energy levels
Restores normal metabolic rate and combats hypothyroid fatigue
Better cognitive function and mental clarity
Improves brain fog, memory, and mental processing speed
Weight management and metabolic health
Supports healthy weight maintenance and metabolic function
Enhanced mood and emotional stability
Reduces depression and improves overall mood stability
Others take these for the same thing
Same goal, different mechanism — check any of them against this one
Melatonin
Sleep support & circadian rhythm
0.5-3mg
A
50%
Boron - Essential Trace Mineral for Bone and Hormone Health
Bone health & hormone support
3-10mg daily
B
85%
Iodine (Thyroid Support)
Thyroid hormone production
150-300mcg
A
95%
Iodine (Potassium Iodide)
Essential thyroid & metabolism support
150-300 mcg
A
95%
Fenugreek
Blood sugar control & testosterone support
500-1000mg
B
75%
Pregnenolone
Brain & hormone precursor
10-50mg daily
B
85%
Every pair we checked
12 combinations scored by the engine
T4 Levothyroxine - Primary Thyroid Hormone + Caffeine
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + Creatine Monohydrate
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + Vitamin D3
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + Calcium Carbonate
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + Whey Protein
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + Lactase
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + Bovine Collagen
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + DHA
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + Turmeric
No documented interaction either way
No known interaction
70
T4 Levothyroxine - Primary Thyroid Hormone + L-Tyrosine
Supports thyroid hormone production
Works better together
78
T4 Levothyroxine - Primary Thyroid Hormone + Selenium (Thyroid Support)
Essential for T4 to T3 conversion
Works better together
82
T4 Levothyroxine - Primary Thyroid Hormone + Iodine (Thyroid Support)
Essential for thyroid hormone synthesis
Works better together
82
Dosage
DailyPRESCRIPTION ONLY - 25-200mcg
Replacement therapyMEDICAL SUPERVISION - 1.6mcg/kg body weight daily
Starting doseMEDICAL SUPERVISION - 25-50mcg daily
Maintenance doseMEDICAL SUPERVISION - 75-200mcg daily
MaximumDoses above 300mcg require intensive medical monitoring
When to expect it
First Effects1-2 weeks for initial metabolic improvements
Peak Benefits6-12 weeks for optimal thyroid hormone replacement
Deficiency DevelopmentT4 deficiency occurs in hypothyroid conditions
Toxicity OnsetOverdose symptoms develop over weeks due to long half-life
How to measure it
MarkerTSH, Free T4, Total T4, Free T3, Anti-TPO antibodies
OptimalFree T4: 0.9-1.7 ng/dL, TSH: 0.5-2.5 mIU/L
Deficient belowFree T4 < 0.8 ng/dL
FrequencyEvery 6-8 weeks during dose adjustment, then every 6-12 months
What actually reaches you
The label counts the carrier, your body does not
Absorption
Very high 80 of 100 · best absorbed form of this compound
Delivered daily
0.1 mg
Cost per 1 mg delivered
$18.52 comparative — uses the absorption score, not a measured percentage
Works better with
+
Selenium
Essential for T4 to T3 conversion
Selenium is cofactor for deiodinase enzymes · level A
+
Iodine
Essential for thyroid hormone synthesis
Iodine is structural component of T4 · level A
+
Tyrosine
Supports thyroid hormone production
Tyrosine is amino acid backbone of thyroid hormones · level BWhat not to take with T4 Levothyroxine - Primary Thyroid Hormone
!
Soy Products
May interfere with T4 absorption and metabolism
Soy isoflavones can affect thyroid hormone function · moderate significance
!
Calcium Iron Fiber
Significantly reduces T4 absorption
Binding and interference with intestinal absorption · high significanceMedication interactions
Discuss these with a pharmacist before combiningT4 enhances anticoagulant effects
What to do: Monitor INR and adjust warfarin dose as needed
T4 may increase insulin requirements
What to do: Monitor blood glucose and adjust medications
Severely reduces T4 absorption
What to do: Separate dosing by at least 4 hours
Available forms
Levothyroxine Sodium (T4): Standard of care, Long half-life, Once daily dosing, Extensive research
Food sources
NO natural food sources of T4
T4 must be synthesized by thyroid gland or taken as medication · N/A
Thyroid glandular supplements
Variable T4 content, not standardized · 60
Prescription levothyroxine
Precise pharmaceutical dosing 25-300mcg · 80
Too little
- T4 deficiency symptoms (hypothyroidism):
- Persistent fatigue and low energy
- Unexplained weight gain and slow metabolism
- Cold intolerance and low body temperature
- Depression and cognitive impairment
- Constipation and digestive issues
- Dry skin, hair loss, and brittle nails
Too much
- T4 excess symptoms (hyperthyroidism):
- Rapid or irregular heartbeat
- Heat intolerance and excessive sweating
- Unintentional weight loss
- Nervousness and anxiety
- Tremors and muscle weakness
- Insomnia and restlessness
Who benefits most
hypothyroidism-primary-treatment
Standard first-line treatment for hypothyroid conditions
MEDICAL SUPERVISION - typically 25-200mcg daily
thyroid-cancer-tsh-suppression
Higher doses used to suppress TSH in thyroid cancer patients
PRESCRIPTION ONLY - specialized oncological dosing
subclinical-hypothyroidism
Low-dose therapy for borderline thyroid function
MEDICAL SUPERVISION - typically 25-75mcg daily
thyroid-hormone-optimization
Precise thyroid hormone replacement for optimal function
MEDICAL SUPERVISION - individualized dosing
elderly-thyroid-replacement
Gentle, stable thyroid replacement for older adults
MEDICAL SUPERVISION - lower starting dosesWhere to buy it
Look for T4 Levothyroxine - Primary Thyroid Hormone at PRESCRIPTION ONLY - 25-200mcg per serving. The form that matters here is Levothyroxine Sodium (T4).
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What else affects it
Beyond other supplements
!
Soy products
May interfere with T4 absorption and metabolism
Soy isoflavones can affect thyroid hormone functionHow it works
- Serves as prohormone converted to active T3 by deiodinase enzymes
- Binds to thyroid hormone receptors after conversion to T3
- Regulates gene expression for metabolic enzymes
- Controls mitochondrial function and energy production
- Influences cardiovascular function and heart rate
- Modulates protein synthesis and cellular growth
Key findings
what the evidence supports- T4 is the standard of care for thyroid hormone replacement therapy
- Provides stable, long-acting thyroid hormone replacement
- Requires conversion to T3 for biological activity
- Generally safe and effective when properly dosed and monitored
Sources: NIH Examine.com · data reviewed 2026-08-01
Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →
Common questions
What are the benefits of T4 Levothyroxine - Primary Thyroid Hormone?
Documented effects: Comprehensive thyroid hormone replacement; Improved metabolism and energy levels; Better cognitive function and mental clarity; Weight management and metabolic health. Provides stable, long-acting thyroid hormone replacement therapy
How much T4 Levothyroxine - Primary Thyroid Hormone should you take per day?
The common daily range is PRESCRIPTION ONLY - 25-200mcg. By goal — replacement therapy: MEDICAL SUPERVISION - 1.6mcg/kg body weight daily; starting dose: MEDICAL SUPERVISION - 25-50mcg daily; maintenance dose: MEDICAL SUPERVISION - 75-200mcg daily; maximum: Doses above 300mcg require intensive medical monitoring.
When is the best time to take T4 Levothyroxine - Primary Thyroid Hormone?
Morning empty stomach. First effects are typically reported within 1-2 weeks for initial metabolic improvements.
What are the side effects of T4 Levothyroxine - Primary Thyroid Hormone?
At excessive doses: T4 excess symptoms (hyperthyroidism):, Rapid or irregular heartbeat, Heat intolerance and excessive sweating, Unintentional weight loss, Nervousness and anxiety. Safety rating at normal doses is 6 out of 10.
What should you not take with T4 Levothyroxine - Primary Thyroid Hormone?
Separate it from Soy Products, Calcium Iron Fiber by two to four hours. May interfere with T4 absorption and metabolism
Does T4 Levothyroxine - Primary Thyroid Hormone interact with medications?
Documented interactions with warfarin-blood-thinners, diabetes-medications, calcium-iron-supplements. Discuss these with a pharmacist before combining.
How do you know if you need T4 Levothyroxine - Primary Thyroid Hormone?
The marker is TSH, Free T4, Total T4, Free T3, Anti-TPO antibodies, optimal range Free T4: 0.9-1.7 ng/dL, TSH: 0.5-2.5 mIU/L. Common deficiency signs: T4 deficiency symptoms (hypothyroidism):, Persistent fatigue and low energy, Unexplained weight gain and slow metabolism, Cold intolerance and low body temperature.