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Thyroid hormone replacement (synthetic T4) · For Dogs

Thyro-Tabs Canine dosage reference for dogs (Levothyroxine)

This page's standard weight-based reference is 0.02 mg per kg (0.0091 mg per lb), with Once daily recorded as the reference frequency. Use the calculator to see the arithmetic for your dog's weight, then confirm the indication, product, and actual dose with a veterinarian.

Onset
Days to weeks for visible improvement
Duration
12-24 hours
Class
Thyroid hormone replacement (synthetic T4)

Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .

This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.

Sources and review process

Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.

Levothyroxine (often known by brand names such as Thyro-Tabs Canine, ThyroKare, and Soloxine) is a synthetic form of the thyroid hormone T4. It is the standard replacement therapy for Hypothyroidism in dogs. Understanding the correct dosage, administration, and monitoring of Levothyroxine is critical for your dog’s safety and well-being.

A typical Levothyroxine starting dose for dogs is around 0.02–0.022 mg/kg (20–22 micrograms per kg) once daily. The FDA-approved Thyro-Tabs Canine label starts at 0.1 mg per 10 lb (0.022 mg/kg) once every 24 hours, and the Merck Veterinary Manual describes about 22 micrograms per kg per day. All amounts on this page are once-daily totals. If your veterinarian splits the daily amount into two doses 12 hours apart, each dose is half of it (for example, 0.01 mg/kg twice daily); always follow your vet’s schedule. Tablets come in strengths from 0.1 mg to 1.0 mg. Because these doses are very small, the calculator shows results in milligrams with two decimal places (0.40 mg = 400 micrograms).

Calculator Warning: Use this only as an educational estimate. Your veterinarian may prescribe a different dose based on your pet’s condition, age, weight, other medications, and medical history.

What the source establishes

The label starts at 0.1 mg per 10 lb (0.022 mg/kg) daily, as one dose every 24 hours or divided every 12 hours, and adjusts by total T4 measured 4 to 6 hours after the tablet every 4 to 8 weeks. It asks owners to give the tablets consistently with or without food, contraindicates use with thyrotoxicosis or uncorrected adrenal insufficiency, and advises close monitoring of dogs with heart disease.

This is one product label. It does not set the maintenance dose for an individual dog, which depends on follow-up blood tests and clinical response.

Thyro-Tabs Canine (levothyroxine sodium) FDA-approved label, NADA 141-448 — Dosage and Administration; Contraindications; Precautions.

Describes levothyroxine at 22 mcg/kg by mouth every 24 hours (or divided twice daily), lifelong, with peak T4 checked 4 to 6 hours after a dose after 4 to 8 weeks of treatment. Lists panting, nervousness, tachycardia, weight loss, and increased thirst and urination as signs of thyrotoxicosis.

A veterinary reference overview. It does not replace diagnosis; thyroid supplementation may be harmful in dogs whose low T4 is caused by another illness.

Merck Veterinary Manual: Hypothyroidism in Animals — Treatment and Control.

Names Thyro-Tabs Canine (every 12 or 24 hours) and ThyroKare (every 12 hours) as FDA-approved, advises giving the drug consistently with or without food, checking thyroid levels every 4 to 8 weeks at first, and watching for panting, nervousness, hyperactivity, and a rapid pulse.

Owner-facing agency guidance. It does not give a dose for any individual dog.

FDA: Hypothyroidism in Dogs — There Are FDA-Approved Drugs to Treat It — Treatment section.

For one approved tablet product (sponsor No. 059051) the regulation states: “0.1 mg/10 lb (0.01 mg/lb, 0.022 mg/kg) body weight twice daily.” That is 0.044 mg/kg per day, the calculator’s daily ceiling.

This is the highest labeled daily amount for an approved product, not a target dose. Most dogs start at 0.022 mg/kg per day and are adjusted by blood tests.

21 CFR 520.1248: Levothyroxine sodium tablets (conditions of use in dogs) — Paragraph (c)(1)(ii).

Lists drugs to use cautiously with levothyroxine, including oral antacids, sucralfate, ferrous sulfate, high fiber, corticosteroids, phenobarbital, anti-diabetic medications, tricyclic antidepressants, sertraline, and ketamine. Advises giving it the same way every day and never giving two doses at once.

Owner-facing hospital handout. It is not a complete interaction list and does not set a dose for any individual dog.

VCA Animal Hospitals: Levothyroxine — Drug interactions; How is it given?.

Levothyroxine Dosage Calculator for Dogs

Enter your dog’s weight below to estimate the once-daily Levothyroxine amount from the 0.02–0.022 mg/kg starting guideline. The result is the total for one day given once every 24 hours; if your vet prescribes twice-daily dosing, each dose is half that amount. Your veterinarian adjusts the dose using follow-up blood tests, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your dog's weight

Quick Dosage Chart

Typical once-daily Levothyroxine amounts for common dog weights, for quick reference:

Dosage Chart · 02

Thyro-Tabs Canine weight-based reference chart for dogs

Scroll sideways to see full table

Thyro-Tabs Canine weight-based reference chart. Educational arithmetic, not a prescription.
Weight Lower Reference Standard Reference Upper Reference Frequency
5 lbs (2.3 kg) 0.045 mg 0.045 mg 0.050 mg Once daily
10 lbs (4.5 kg) 0.091 mg 0.091 mg 0.100 mg Once daily
15 lbs (6.8 kg) 0.14 mg (1.25 × 0.1mg) 0.14 mg (1.25 × 0.1mg) 0.15 mg Once daily
20 lbs (9.1 kg) 0.18 mg (1.75 × 0.1mg) 0.18 mg (1.75 × 0.1mg) 0.20 mg Once daily
25 lbs (11.3 kg) 0.23 mg (0.75 × 0.3mg) 0.23 mg (0.75 × 0.3mg) 0.25 mg Once daily
30 lbs (13.6 kg) 0.27 mg (2.5 × 0.1mg) 0.27 mg (2.5 × 0.1mg) 0.30 mg Once daily
40 lbs (18.1 kg) 0.36 mg (1.25 × 0.3mg) 0.36 mg (1.25 × 0.3mg) 0.40 mg Once daily
50 lbs (22.7 kg) 0.45 mg (4.5 × 0.1mg) 0.45 mg (4.5 × 0.1mg) 0.50 mg Once daily
60 lbs (27.2 kg) 0.54 mg (5.5 × 0.1mg) 0.54 mg (5.5 × 0.1mg) 0.60 mg Once daily
70 lbs (31.7 kg) 0.63 mg (1.25 × 0.5mg) 0.63 mg (1.25 × 0.5mg) 0.70 mg Once daily
80 lbs (36.3 kg) 0.73 mg (7.5 × 0.1mg) 0.73 mg (7.5 × 0.1mg) 0.80 mg Once daily
90 lbs (40.8 kg) 0.82 mg (8 × 0.1mg) 0.82 mg (8 × 0.1mg) 0.90 mg Once daily
100 lbs (45.4 kg) 0.91 mg (9 × 0.1mg) 0.91 mg (9 × 0.1mg) 1.00 mg Once daily
120 lbs (54.4 kg) 1.1 mg (11 × 0.1mg) 1.1 mg (11 × 0.1mg) 1.2 mg Once daily
150 lbs (68 kg) 1.4 mg (13.5 × 0.1mg) 1.4 mg (13.5 × 0.1mg) 1.5 mg Once daily

Parenthetical tablet amounts are arithmetic comparisons only. They do not account for scoring, release type, concentration, product labeling, or whether this medication is appropriate for an individual animal.

By Weight

Thyro-Tabs Canine reference by dog weight

Choose a common weight to open its optional reference page. Use the main medication calculator for a different exact weight.

Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.

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How to Give Levothyroxine to Your Dog

Give levothyroxine by mouth at the same time every day, exactly as prescribed. Most dogs get the whole daily amount once every 24 hours; if your vet splits it into two doses 12 hours apart, each dose is half the daily amount. Keep it consistent with meals — always with food or always without — because food changes absorption. Doses are very small (often under 1 mg), so check the tablet strength on every refill. If a dose is missed, give it when you remember unless the next dose is nearly due; never give two doses at once. Wash your hands after handling tablets and store the bottle where pets and children cannot reach it.

Food reduces how much levothyroxine is absorbed, so the FDA-approved label asks owners to give it consistently either with or without food, and the Merck Veterinary Manual describes giving it on an empty stomach. It may interact with oral antacids and sucralfate, iron supplements and high-fiber diets, corticosteroids, phenobarbital, insulin and other diabetes medications, some antidepressants, ketamine, and heart medications. Tell your veterinarian about every medication and supplement your dog takes.

Your veterinarian will recheck a total T4 blood test, usually 4 to 8 weeks after starting or changing the dose. The sample is typically drawn 4 to 6 hours after the pill, when levels peak, so ask your clinic when to give the dose on test day. Once the dose is stable, rechecks continue at regular intervals.

Side Effects and Safety

Side effects are uncommon at appropriate doses. Problems reported in dogs treated with levothyroxine include Decreased appetite, Vomiting or diarrhea, Itching or skin irritation, and Lethargy. Giving too much can cause thyrotoxicosis, with panting, nervousness, hyperactivity, a rapid heart rate, increased thirst and urination, and weight loss. Allergic reactions such as hives or facial swelling have also been reported.

Levothyroxine should not be used in dogs with thyrotoxicosis or untreated Addison’s disease (adrenal insufficiency). Dogs with heart disease need close monitoring while the dose is being established, and their heart medications or levothyroxine dose may need adjusting. Use caution in dogs with diabetes and in elderly dogs.

Cautions · 12

When Thyro-Tabs Canine should be used with caution or avoided

Some dogs should not take Thyro-Tabs Canine, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Thyro-Tabs Canine.

  • Thyrotoxicosis (excess thyroid hormone)
  • Uncorrected adrenal insufficiency (untreated Addison’s disease)
  • Use with caution in dogs with heart disease, diabetes, managed Addison’s disease, or in elderly dogs

Interactions · 13

Thyro-Tabs Canine drug interactions

Thyro-Tabs Canine can interact with other drugs. This list is not complete — always give your veterinarian a full list of your dog's medications and supplements.

Oral antacids and sucralfate
Iron supplements (ferrous sulfate) and high-fiber diets
Corticosteroids
Phenobarbital
Insulin and other diabetes medications
Tricyclic antidepressants and sertraline
Ketamine
Heart medications (doses may need adjusting)

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult dog at a known weight. Do not rely on it in these situations — talk to your veterinarian instead:

  • In an emergency, or after accidental ingestion or a suspected overdose
  • For pregnant or nursing pets
  • For very young or very old dogs
  • For pets with liver disease, kidney disease, or another chronic illness
  • For pets taking several medications at once
  • When you are not sure of your dog's current, accurate weight
  • For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

If you think your dog had too much Thyro-Tabs Canine, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.

  • Call your veterinarian or the nearest emergency animal hospital.
  • ASPCA Animal Poison Control Center: (888) 426-4435
  • Pet Poison Helpline: (855) 764-7661

A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.

When to Call the Vet

If your dog experiences any of the following, contact your veterinarian or an emergency clinic immediately:

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

What is a typical levothyroxine starting dose for dogs?
The FDA-approved Thyro-Tabs Canine label starts at 0.1 mg per 10 pounds (0.022 mg/kg, about 20 micrograms per kg) per day. The amounts on this page are that once-daily total. For a 20 kg (44 lb) dog that works out to roughly 0.40–0.44 mg once a day. Your veterinarian then adjusts the dose based on blood tests and how your dog responds, so the final dose often differs from the starting one.
What if my vet prescribes levothyroxine twice a day?
The calculator and chart show the total amount for one day, given once every 24 hours. Some vets split that daily total into two doses 12 hours apart; each of those doses is then half the daily amount (for example, 0.02 mg/kg a day becomes 0.01 mg/kg twice daily). Always follow the schedule and dose your veterinarian prescribes, and never give the full daily amount twice in one day unless your vet has told you to.
Why does the thyroid blood test need to be taken 4-6 hours after the pill?
Levothyroxine levels peak a few hours after each dose. The Thyro-Tabs Canine label and the Merck Veterinary Manual both describe checking total T4 about 4 to 6 hours after the tablet, typically 4 to 8 weeks after starting or changing the dose. Ask your clinic exactly when to give the pill on test day so the sample is timed correctly.
Should levothyroxine be given with or without food?
Food reduces how much levothyroxine is absorbed, so the label asks owners to give it consistently — either always with food or always without. The Merck Veterinary Manual describes giving it on an empty stomach. The most important thing is to keep the routine the same every day so blood tests reflect a stable pattern.
How long will my dog need levothyroxine?
Hypothyroidism in dogs is usually permanent, so levothyroxine is typically a lifelong daily medication. Energy and activity often improve within days to weeks, while skin and coat changes can take longer. Do not stop the medication without talking to your veterinarian, because signs will return.
Can I switch between brands, generics, or a compounded levothyroxine?
Not without your veterinarian. The Thyro-Tabs Canine label notes that starting doses and bioavailability can differ between products, so a recheck of T4 and clinical signs is recommended after any switch. Tablets are sold in strengths from 0.1 mg to 1.0 mg, and the color and strength can differ by product, so double-check each refill.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your dog's weight by the lower, standard, and upper mg/kg values recorded for Thyro-Tabs Canine. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses
Hypothyroidism, Thyroid hormone replacement therapy
Recorded forms
Tablet, Oral solution (outside the US)
Reference timing
Once daily; onset Days to weeks for visible improvement; duration 12-24 hours

Individual checks a calculator cannot perform

  • Confirm the diagnosis and the reason this medication is being considered.
  • Match the exact product, concentration, route, and whether a tablet may be split.
  • Account for age, pregnancy, organ function, genetics, allergies, and prior reactions.
  • Review every prescription, over-the-counter product, and supplement your pet takes.

Recorded cautions

Thyrotoxicosis (excess thyroid hormone); Uncorrected adrenal insufficiency (untreated Addison’s disease); Use with caution in dogs with heart disease, diabetes, managed Addison’s disease, or in elderly dogs.

Recorded interactions

Oral antacids and sucralfate; Iron supplements (ferrous sulfate) and high-fiber diets; Corticosteroids; Phenobarbital; Insulin and other diabetes medications; Tricyclic antidepressants and sertraline; Ketamine; Heart medications (doses may need adjusting).

These lists reproduce the structured record used by this page and may not be exhaustive. Show your veterinarian the product label and your dog's complete medication list before acting on a number.

Sources · 09

Sources & references

The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.

Specific citations above support the identified claims. Other source names remain record-level references; further claim review is still needed. Read our methodology and limitations.

Transparency · 11

How this page was made

This page's structured medication record lists the source names below. PetDosageChart applies the record's mg/kg values to the entered weight and presents the arithmetic result. A source record is not the same as an individualized prescription or an independent clinical review.

Sources cited
  • Merck Veterinary Manual
  • Thyro-Tabs Canine FDA-approved label (NADA 141-448)
  • FDA: Hypothyroidism in Dogs (Animal Health Literacy)
  • VCA Animal Hospitals: Levothyroxine
  • 21 CFR 520.1248 (levothyroxine sodium tablets, conditions of use)
Calculator formula
Doses scale linearly from a standard basis of 0.02 mg per kg (0.0091 mg per lb) of body weight, given Once daily. The calculator multiplies that basis by your dog's weight and shows an arithmetic comparison with recorded tablet sizes. That comparison does not determine whether a tablet is scored, splittable, or appropriate for your pet.
Editorial owner
Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
DVM review status
Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.

More on our methodology and editorial process — how we source, calculate, and review dogs dosage data.

Safety · 10

More resources