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Halycil: Uses, Side Effects and Dosage

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Prescription (Rx)
Strength:
50 mg
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Source: Health Canada – Drug Product Database (DPD) and product monographs · About this document

Patient Medication Information: uses, side effects, how to take - Halycil

Serious Warnings and Precautions

What HALYCIL® is used for:

HALYCIL® is used in adults:

  • to treat hyperthyroidism (overactive thyroid gland);
  • to speed up recovery when used in combination with radioactive iodine therapy;
  • to control symptoms of hyperthyroidism before surgery; and
  • to manage symptoms of a thyroid storm (thyroid gland produces too much thyroid hormones in a short period of time).

How HALYCIL® works:

HALYCIL® belongs to a group of medications called antithyroid medicines. It works by stopping the thyroid gland from making thyroid hormones. This medication may take a few weeks to reduce the symptoms of hyperthyroidism.

  • Agranulocytosis (low white blood cells): Treatment with HALYCIL® can cause agranulocytosis, especially during the initial three months of treatment. This can lead to serious complications or even death. The symptoms can include unusual bleeding, fever, sore throat, bruising, or skin rashes. Your healthcare professional will monitor your health throughout your treatment. However, if you notice any of these symptoms tell your healthcare professional right away. They will stop your treatment if agranulocytosis is suspected.
  • Liver problems: Treatment with HALYCIL® can cause liver injury leading to liver problems, liver failure, or death. This usually occurs during the initial two months of treatment. The symptoms can include: anorexia, itchiness, yellowing of the eyes or skin, light coloured stools, dark urine, and abdominal pain. If these occur your healthcare professional will assess your liver and may decide to stop your treatment.

The ingredients in HALYCIL® are:

Medicinal ingredient: propylthiouracil.

Non-medicinal ingredients: acacia spray-dried, croscarmellose sodium, lactose monohydrate, magnesium stearate and sodium laurilsulfate.

HALYCIL® comes in the following dosage forms:

Tablets: 50 mg of propylthiouracil.

Do not use HALYCIL® if:

  • you are allergic to propylthiouracil or any of the other ingredients in HALYCIL®;
  • you are allergic to similar antithyroid medications known as thioamide derivatives. Ask your healthcare professional if you are unsure;
  • you are breast-feeding or planning to breastfeed.

To help avoid side effects and ensure proper use, talk to your healthcare professional before you take HALYCIL®. Talk about any health conditions or problems you may have, including if you:

  • have a low white blood cell count;
  • have joint pain;
  • have asthma;
  • have skin problems;
  • have or have had liver problems;
  • are taking medications known to be associated with agranulocytosis (ask your healthcare professional if you are unsure);
  • have inflamed blood vessels (vasculitis);
  • have or have had kidney problems;
  • are intolerant to some sugars (e.g., lactose, a milk sugar which is a component of HALYCIL®);
  • are taking an anticoagulant (medications used to prevent your blood from clotting);
  • are planning to have surgery;
  • are pregnant, think you may be pregnant or plan to become pregnant.

Other warnings you should know about:

  • Vasculitis (inflammation of the blood vessel): Treatment with HALYCIL® can cause vasculitis, which can lead to severe organ damage or death. This can occur to the blood vessels in your kidneys, skin, lungs, brain, and intestine. The symptoms of vasculitis include blood in your urine, less urine, a new rash, shortness of breath, or coughing up blood. If you notice any of these symptoms tell your healthcare professional. They may discontinue your treatment and may initiate the appropriate intervention.
  • Hypothyroidism (thyroid gland is producing not enough thyroid hormone): Treatment with HALYCIL® can cause hypothyroidism. The symptoms can include weight gain, tiredness, hair loss, muscle weakness, feeling cold, dry skin, constipation, puffy face, heavier than normal or irregular menstrual periods, and enlarged thyroid gland. If signs of hypothyroidism occur, tell your healthcare professional. They may reduce or temporarily stop your treatment and may also perform tests to measure your hormone levels. • Skin rashes: Treatment with HALYCIL® can cause skin rashes. This can be a sign of an allergic reaction or a skin reaction. If you notice a skin rash stop taking HALYCIL® right away and tell your healthcare professional.
  • Blood problems: Treatment with HALYCIL® can cause decreased levels of red blood cells, white blood cells, and/or blood platelets. Your healthcare professional may do blood tests to monitor the profile of your blood. They may decide to reduce or stop your dose of HALYCIL®.

See the Serious side effects and what to do about them table, below, for more information on these and other serious side effects.

Monitoring and Testing:

Your healthcare professional will monitor your health which can include doing blood tests. These tests may be performed before and periodically during your treatment to assess the functions of your liver, thyroid, blood, and blood clotting. This will tell your healthcare professional how HALYCIL® is affecting you.

Pregnancy:

  • You should use effective birth control while taking HALYCIL® to avoid potential risks.
  • If you become pregnant or think you are pregnant while taking HALYCIL®, tell your healthcare professional right away.
  • If you are pregnant or are able to become pregnant, there are specific risks for you and your unborn baby that you must discuss with your healthcare professional.
  • If you are prescribed HALYCIL® while you are pregnant, your healthcare professional will also closely monitor you and your unborn baby to ensure that HALYCIL® is working correctly. They may also switch your treatment after the first trimester of your pregnancy.

Tell your health professional about all the medicines you take, including any drugs, vitamins, minerals, natural supplements or alternative medicines.

The following may interact with HALYCIL®:

  • medicines that might need a reduced dose when hyperthyroid patients become euthyroid such as:

    • Theophylline, a drug used to treat asthma;
    • Digoxin, used to treat problems with the rhythm of your heart;
    • Beta-Blockers, used to treat high blood pressure.

You should not take HALYCIL® before you have radio-iodine (131I) therapy for an overactive thyroid gland (hyperthyroidism) because it can reduce the effectiveness of radio-iodine (131I) therapy.

Serious Drug Interactions

How to take HALYCIL®:

  • You can take HALYCIL® with or without food.

  • Swallow the tablets whole with a drink of water. Do not chew, split, or crush tablets. If the tablet is broken, cracked, or otherwise not intact, do not take the tablet.

Usual dose:

Your healthcare professional will tell you how many tablets to take, and when to take them each day. This will depend on your condition, what other medicines you are taking, and how you respond to treatment with HALYCIL®.

When your condition has improved your healthcare professional may put you on a lower dose to maintain your condition.

Overdose:

You may need urgent medical attention in the case of an overdose. Signs that you have taken too many tablets include vomiting, stomach pain, headache, fever, joint pain, itching, being pale, tiredness, frequent infections, unusual bleeding or unexplained bruising.

An overdose can also lead to the following:

  • agranulocytosis (low white blood cells);
  • hypothyroidism (thyroid gland is producing not enough thyroid hormone), in which case you may feel tired, cold, or put on weight.;
  • hemorrhage (blood loss).
If you think you, or a person you are caring for, have taken too much HALYCIL, contact a healthcare professional, hospital emergency department, regional poison control centre or Health Canada’s toll-free number, 1-844 POISON-X (1-844-764-7669) immediately, even if there are no signs or symptoms.

Missed Dose:

Do not take a double dose to make up for a missed dose. If you forget to take a dose, take it as soon as you remember. If it is almost time for your next dose, then do not take the missed dose at all. If you are not sure what to do, ask your healthcare professional.

  • Taking HALYCIL® with anticoagulants (medicines used to prevent blood clots or thin the blood such as warfarin or heparin), can increase your risk of hypoprothrombinemia (low prothrombin, a blood clotting substance). Ask your healthcare professional if you are unsure.
  • Taking HALYCIL® with any medications that may lead to agranulocytosis (low white blood cells) may increase your risk of agranulocytosis. Ask your healthcare professional if you are unsure.

Possible side effects from using HALYCIL®:

These are not all the possible side effects you may have when taking HALYCIL®. If you experience any side effects not listed here, tell your healthcare professional.

Side effects may include:

  • abdominal discomfort (vomiting, nausea, gastrointestinal disturbances);
  • muscle and/or joint pain;
  • back pain
  • drowsiness (feeling sleepy)
  • dizziness (feeling light-headed)
  • a tingling or prickling feeling in the hands, arms, legs, or feet
  • loss of taste (taste changes)
  • hair loss or change in hair colour
  • mild skin rashes or itching, skin discolouration
  • headaches
  • changes in hearing (ringing in ears, etc.)
  • swelling of hands, arms, feet, ankles, and legs

Serious side effects and what to do about them

Frequency/Side Effect/SymptomTalk to your health professionalStop taking drug and get immediate medical help
Only if severeIn all cases
Uncommon
Liver problems (including inflammation or damage to the liver, and the death of liver cells): yellowing of the skin or eyes (jaundice), stomach pain or swelling, nausea, vomiting, unusual dark urine, unusual tiredness, fever, light-coloured stool, urine turns dark, and loss of appetite for several days or longer√
Kidney problems (including kidney failure and kidney inflammation (nephritis)): blood in the urine, bruises and blood spots, breathlessness, coughing, swelling of your lymph glands (glands situated around the body which protect against the spread of infection), swelling of the blood vessels in your skin, pain in your lower back / less oxygen to the body, development of anemia√
Serious side effects and what to do about them
Frequency/Side Effect/SymptomTalk to your health professionalStop taking drug and get immediate medical help
Only if severeIn all cases
Agranulocytosis (low white blood cells): swollen lymph nodes, fever, sore throat, rashes or ulcers in your mouth and throat, bruising, discomfort, unusual bleeding, infections, or chills√
Rare
Interstitial lung disease (inflammation and scarring of lung tissue): shortness of breath that gets worse with exercise, dry cough, tiredness, chest discomfort√
Aplastic anemia (when cells meant to develop into mature blood cells are damaged): fatigue, weakness, and pale skin√
Very rare
Vasculitis (inflammation of the blood vessels): blood in your urine, less urine, a new rash, shortness of breath, coughing up blood, fever, fatigue, weight loss, and general aches or pains√
Leukopenia (low white blood cells): infections, swollen lymph nodes, fatigue, fever, aches, pains, and flu-like symptoms√
Thrombocytopenia (low blood platelets): bruising or bleeding for longer than usual if you hurt yourself, fatigue, and weakness√
Hypothyroidism (thyroid gland is producing not enough thyroid hormone): tiredness, lethargy, muscle weakness, cramps, feeling cold, a slow heart rate, dry, puffy, flaky skin, hair loss, a deep and husky voice, unusual weight gain, change in menstrual periods, listlessness, constipation, headache, and puffy face√
Serious side effects and what to do about them
Frequency/Side Effect/SymptomTalk to your health professionalStop taking drug and get immediate medical help
Only if severeIn all cases
Allergic reactions: fever, skin rash, hives, itching, swelling, shortness of breath, wheezing, runny nose, itchy, watery eyes, redness, blistering and/or peeling of the skin and/or inside of the lips, eyes, mouth, nasal passages or genitals, chills, headache, cough, body aches or swollen glands, and redness√
Encephalopathy (a disease that affects the function or structure of the brain): loss of memory, cognitive impairment, personality changes, inability to concentrate, laziness, coordination or balance problems, muscle twitches, sleep problems, and slurred speech√
Anemia (low red blood cells): fatigue, loss of energy, irregular heartbeats, pale complexion, shortness of breath, and weakness√
Hypoprothrombinemia (low prothrombin, a blood clotting substance): bleeding or bruising easily, blood in stool, blood in urine, gums bleed easily, nosebleeds, and swelling or pain in your joints√
Lupus-like syndrome: fever, joint swelling and pain, muscle aches, blood in urine, shortness of breath, or rash√
Unknown
Serious side effects and what to do about them
Frequency/Side Effect/SymptomTalk to your health professionalStop taking drug and get immediate medical help
Only if severeIn all cases
Severe skin reactions, including Stevens-Johnson Syndrome (SJS) and toxic epidermal necrolysis (TEN): a widespread rash with blisters and peeling skin around the mouth, nose, eyes and genitals, extensive peeling of the skin (more than 30% of the body), ulcers, or lesions√

If you have a troublesome symptom or side effect that is not listed here or becomes bad enough to interfere with your daily activities, tell your healthcare professional.

Reporting Side Effects

You can report any suspected side effects associated with the use of health products to Health Canada by:

  • Visiting the Web page on Adverse Reaction Reporting (https://www.canada.ca/en/health-canada/services/drugs-health-products/medeffect-canada/adverse-reaction-reporting.html) for information on how to report online, by mail or by fax;

    or

  • Calling toll-free at 1-866-234-2345.

NOTE: Contact your healthcare professional if you need information about how to manage your side effects. The Canada Vigilance Program does not provide medical advice.

Storage:

Do not store HALYCIL® above 30°C. Store in the original package in order to protect from light.

Keep this medicine out of the sight and reach of children.

If you want more information about HALYCIL®:

  • Talk to your healthcare professional.

  • Find the full Product Monograph that is prepared for healthcare professionals and includes this Patient Medication Information by visiting the Health Canada website (https://www.canada.ca/en/health-canada/services/drugs-health-products/drug-products/drug-product-database.html); the manufacturer’s (Halewood Chemicals Ltd.) website

    www.halewoodchemicals.com, the Canadian distributor’s (Accelera Pharma Canada Inc.) website http://apcipharma.com/ or by calling 1-855-611-2724.

Staines, Middlesex, TW19 6BJ, United Kingdom

Date of Authorization: September 16, 2026

About this document

Source: Health Canada – Drug Product Database (DPD) and product monographs · DIN (Drug Identification Number): 02521059

Approved according to the text: September 16, 2026

Found a mistake? Write to us via the contact page.

The information on this site does not replace the advice of a doctor or pharmacist.

Drug information for Halycil

Rx or OTC
Prescription (Rx)?
DIN 02521059
Schedule(s) PRESCRIPTION
Active ingredient(s) Propylthiouracil 50 MG
Dosage form(s) Tablet
Route(s) of administration Oral
Drug class (WHO ATC)
  1. H Systemic hormonal preparations, excl. sex hormones and insulins
    1. H03 Thyroid therapy drugs
      1. H03B Antithyroid preparations
        1. H03BA Thiouracil antithyroid preparations
          1. H03BA02 Propylthiouracil
Company HALEWOOD CHEMICALS LIMITED
Current status Marketed
Current status date March 23, 2022

Source: Health Canada – Drug Product Database (DPD) and product monographs, data as of November 1, 2026. Data from the Health Canada Drug Product Database, as published there. Not a substitute for the advice of a doctor or pharmacist.