Fultium (Colecalciferol / Vitamin D3)
Prescription vitamin D3 supplement for the prevention and treatment of vitamin D deficiency
Quick facts about Fultium
Key Takeaways About Fultium
- Fultium treats vitamin D deficiency: It contains colecalciferol (vitamin D3), the same form of vitamin D produced naturally in the skin by sunlight exposure
- Essential for bone health: Vitamin D3 promotes calcium and phosphorus absorption, helping prevent osteoporosis, rickets, and osteomalacia
- Take with food for best absorption: Vitamin D is fat-soluble, so taking Fultium with a meal containing dietary fat significantly improves absorption
- Monitor calcium levels in high doses: Excessive vitamin D supplementation can lead to hypercalcaemia, a potentially serious condition requiring medical monitoring
- Wide-ranging health benefits: Beyond bone health, adequate vitamin D levels support immune function, muscle strength, and may reduce the risk of certain chronic diseases
What Is Fultium and What Is It Used For?
Fultium is a prescription medication containing colecalciferol (vitamin D3) used to treat and prevent vitamin D deficiency. It is available as 400 IU soft capsules and helps the body absorb calcium and phosphorus, which are critical for maintaining healthy bones, teeth, and muscle function.
Vitamin D deficiency is one of the most prevalent nutritional deficiencies in the world, affecting an estimated one billion people across all age groups and ethnicities. The World Health Organization (WHO) recognises vitamin D deficiency as a significant public health concern, particularly in regions with limited sunlight exposure, among elderly populations, and in individuals with darker skin pigmentation who produce less vitamin D from sun exposure.
Fultium contains colecalciferol, also known as vitamin D3 or cholecalciferol. This is the same form of vitamin D that the human body naturally produces when the skin is exposed to ultraviolet B (UVB) radiation from sunlight. Vitamin D3 is considered the preferred form of supplementation because it is more effective at raising and maintaining serum 25-hydroxyvitamin D [25(OH)D] levels compared to vitamin D2 (ergocalciferol), the plant-derived alternative.
Once ingested, colecalciferol undergoes two hydroxylation steps in the body. First, it is converted to calcifediol (25-hydroxyvitamin D) in the liver, which is the primary circulating form of vitamin D measured in blood tests. It is then further converted in the kidneys to calcitriol (1,25-dihydroxyvitamin D), the biologically active hormonal form that acts on vitamin D receptors (VDRs) found throughout the body.
Fultium is prescribed for a number of clinical indications, including:
- Treatment of vitamin D deficiency (serum 25(OH)D levels below 25 nmol/L or 10 ng/mL)
- Prevention of vitamin D deficiency in at-risk populations, such as the elderly, pregnant women, and individuals with limited sun exposure
- Adjunct treatment for osteoporosis, typically alongside calcium supplementation and anti-resorptive therapy
- Prevention and treatment of osteomalacia (softening of the bones in adults) and rickets (bone deformity in children)
- Support of calcium metabolism in patients with conditions affecting calcium absorption, such as malabsorption syndromes
Vitamin D plays a crucial role far beyond bone health. It regulates over 200 genes involved in cell growth, immune modulation, and neuromuscular function. Research from the Endocrine Society and other leading bodies has linked adequate vitamin D status to reduced risk of falls in the elderly, improved immune defence against respiratory infections, and better overall musculoskeletal function. The discovery of vitamin D receptors in nearly every tissue of the body has expanded our understanding of its wide-ranging physiological importance.
What Should You Know Before Taking Fultium?
Before starting Fultium, inform your doctor about any history of kidney disease, high calcium levels (hypercalcaemia), kidney stones, or sarcoidosis. Certain medications can interact with colecalciferol, and dose adjustments may be necessary for specific patient populations.
While vitamin D supplementation is generally considered safe at recommended doses, there are important precautions and contraindications that must be considered before starting treatment with Fultium. Your prescribing healthcare provider should have a complete picture of your medical history and current medications to ensure safe and effective use.
Contraindications
You should not take Fultium if you have any of the following conditions:
- Hypercalcaemia – abnormally high levels of calcium in the blood, as vitamin D will further increase calcium absorption
- Hypercalciuria – excessive calcium excretion in the urine, which increases the risk of kidney stone formation
- Nephrolithiasis – existing calcium-containing kidney stones, as additional calcium absorption may worsen the condition
- Hypervitaminosis D – vitamin D toxicity from excessive prior supplementation
- Known allergy to colecalciferol or any of the excipients in the Fultium capsule formulation, including peanut oil or soya (some formulations contain these)
Warnings and Precautions
Exercise caution and discuss with your doctor if you have any of the following:
- Renal impairment: Patients with kidney disease may have impaired ability to convert vitamin D to its active form and are at higher risk of developing hypercalcaemia. Careful monitoring of serum calcium and phosphate levels is essential.
- Sarcoidosis: This granulomatous disease can cause unregulated conversion of vitamin D to its active form (calcitriol), leading to hypercalcaemia even with standard doses of supplementation.
- Primary hyperparathyroidism: Patients may be more sensitive to the effects of vitamin D, and supplementation should be carefully monitored.
- Immobilisation: Prolonged immobility increases the risk of hypercalcaemia when taking vitamin D and calcium supplements.
- Concomitant calcium supplementation: When taking both vitamin D and calcium supplements, monitoring of serum calcium levels is recommended to avoid hypercalcaemia.
During long-term treatment with Fultium at higher doses, periodic monitoring of serum calcium levels, urinary calcium excretion, and renal function is recommended. This is particularly important in elderly patients and those receiving concurrent treatment with cardiac glycosides or diuretics.
Pregnancy and Breastfeeding
Vitamin D supplementation during pregnancy is widely recommended by leading health organisations including the WHO, the Royal College of Obstetricians and Gynaecologists (RCOG), and the American College of Obstetricians and Gynecologists (ACOG). Vitamin D deficiency during pregnancy has been associated with adverse outcomes including pre-eclampsia, gestational diabetes, low birth weight, and impaired fetal skeletal development.
However, high doses of vitamin D should be avoided during pregnancy unless specifically prescribed and monitored by a healthcare provider. Hypercalcaemia caused by excessive vitamin D intake during pregnancy may be harmful to the developing fetus, potentially causing supravalvular aortic stenosis, retinopathy, and neonatal hypercalcaemia. The generally recommended daily intake during pregnancy is 400–600 IU (10–15 mcg), although some guidelines suggest up to 1,000–2,000 IU daily for women with documented deficiency.
Colecalciferol and its metabolites are excreted in breast milk. Supplementation at standard doses is generally considered compatible with breastfeeding and may help ensure adequate vitamin D status in both mother and infant. Many paediatric guidelines now recommend that exclusively breastfed infants receive a vitamin D supplement of 400 IU daily, as breast milk alone typically does not provide sufficient vitamin D.
Do not exceed the prescribed dose of Fultium without consulting your doctor. Vitamin D toxicity (hypervitaminosis D) can cause dangerous hypercalcaemia, leading to nausea, vomiting, excessive thirst, kidney damage, and potentially life-threatening cardiac arrhythmias. The tolerable upper intake level (UL) for adults is 4,000 IU (100 mcg) per day according to most international guidelines.
How Does Fultium Interact with Other Drugs?
Fultium (colecalciferol) can interact with several classes of medications, including thiazide diuretics, cardiac glycosides, anticonvulsants, and lipid-lowering agents. Some drugs reduce vitamin D absorption, while others may increase the risk of hypercalcaemia when combined with vitamin D supplementation.
Drug interactions with colecalciferol can be clinically significant and may require dose adjustments, additional monitoring, or timing modifications. It is essential to inform your healthcare provider about all medications you are currently taking, including prescription drugs, over-the-counter preparations, and herbal supplements. The following table summarises the most important known drug interactions with Fultium.
Major Interactions
These interactions may have significant clinical consequences and require close medical supervision:
| Interacting Drug | Effect | Clinical Recommendation |
|---|---|---|
| Thiazide diuretics (e.g. hydrochlorothiazide, bendroflumethiazide) | Reduced renal calcium excretion, increasing risk of hypercalcaemia | Monitor serum calcium regularly; adjust vitamin D dose if needed |
| Cardiac glycosides (e.g. digoxin) | Hypercalcaemia from vitamin D may potentiate digoxin toxicity, causing arrhythmias | Close cardiac monitoring; regular serum calcium and digoxin level checks |
| Phosphate-binding antacids (e.g. aluminium hydroxide) | Vitamin D increases aluminium absorption, potentially causing toxicity in renal impairment | Avoid concurrent use in patients with renal impairment |
Minor Interactions
These interactions may reduce the effectiveness of Fultium or require timing adjustments:
| Interacting Drug | Effect | Clinical Recommendation |
|---|---|---|
| Anticonvulsants (e.g. phenytoin, carbamazepine, phenobarbital) | Increase hepatic metabolism of vitamin D, reducing its effectiveness | Higher vitamin D doses may be needed; monitor 25(OH)D levels |
| Rifampicin | Potent CYP enzyme inducer that accelerates vitamin D metabolism | Increase vitamin D dose; monitor serum levels |
| Orlistat | Reduces absorption of fat-soluble vitamins including vitamin D | Take Fultium at least 2 hours before or after orlistat |
| Cholestyramine / Colestipol | Bile acid sequestrants reduce intestinal absorption of vitamin D | Take Fultium at least 2 hours before or 4–6 hours after |
| Glucocorticoids (e.g. prednisolone) | May impair vitamin D metabolism and calcium absorption | Higher vitamin D doses often required with long-term steroid use |
| Isoniazid | Inhibits conversion of vitamin D to its active form | Monitor vitamin D levels in patients on long-term isoniazid therapy |
Additionally, patients taking other vitamin D-containing supplements or fortified foods should be aware of the total daily vitamin D intake to avoid inadvertent overdosing. Many multivitamins, calcium supplements, and fortified food products contain vitamin D, and the cumulative intake from all sources should be considered when establishing the appropriate Fultium dose.
What Is the Correct Dosage of Fultium?
The correct dosage of Fultium depends on the indication, severity of deficiency, and patient population. For treating vitamin D deficiency in adults, typical doses range from 800 to 4,000 IU daily. For prevention, 400–800 IU daily is generally recommended. Your doctor will determine the appropriate dose based on your blood test results.
Dosing of Fultium should be individualised based on clinical assessment, baseline serum 25-hydroxyvitamin D levels, and the specific indication for treatment. The following guidelines are based on recommendations from the Endocrine Society, NICE (National Institute for Health and Care Excellence), and the Institute of Medicine (IOM). Your prescribing healthcare provider will determine the most appropriate dose for your individual circumstances.
Adults
Treatment of Vitamin D Deficiency
For documented vitamin D deficiency (serum 25(OH)D below 25 nmol/L): Loading dose of 40,000–50,000 IU weekly for 6–8 weeks (using higher-strength preparations), followed by a maintenance dose of 800–2,000 IU daily. When using Fultium 400 IU capsules, 2–5 capsules daily may be prescribed for maintenance.
Prevention / Maintenance
For prevention of deficiency in at-risk adults: 400–800 IU daily (1–2 Fultium 400 IU capsules). The Endocrine Society recommends at least 600–1,000 IU daily for most adults, with higher doses of 1,500–2,000 IU daily for those at risk of deficiency.
Osteoporosis Adjunct
As an adjunct to osteoporosis treatment: 800–1,000 IU daily (2–3 capsules), typically combined with calcium supplementation of 1,000–1,200 mg daily. This is in line with the International Osteoporosis Foundation and NICE recommendations.
Children
Infants (0–12 months)
400 IU daily is recommended for all breastfed infants and formula-fed infants consuming less than 1 litre of formula per day, as per the American Academy of Pediatrics (AAP) and WHO guidelines. This dose is suitable for prevention of rickets and maintaining adequate vitamin D status.
Children (1–18 years)
For prevention: 400–600 IU daily (1 Fultium capsule). For treatment of deficiency: 1,000–2,000 IU daily for 6–8 weeks, then reassess levels. Children at high risk of deficiency (limited sun exposure, darker skin, obesity) may require higher maintenance doses as determined by their paediatrician.
Elderly
Adults Over 65 Years
Elderly individuals are at particularly high risk of vitamin D deficiency due to reduced skin synthesis, decreased dietary intake, and impaired renal hydroxylation. The recommended dose for prevention is 800–2,000 IU daily. NICE and the British Geriatrics Society recommend that all adults over 65 take at least 800 IU daily to reduce the risk of falls and fractures. Care home residents should receive supplementation regardless of season.
Missed Dose
If you forget to take a dose of Fultium, take it as soon as you remember on the same day. If you do not remember until the next day, skip the missed dose and continue with your regular schedule. Do not take a double dose to make up for a forgotten capsule. Vitamin D is stored in body fat tissue and has a long half-life (approximately 2–3 weeks for colecalciferol), so missing a single dose is unlikely to have significant clinical impact.
Overdose
Vitamin D toxicity (hypervitaminosis D) is rare at recommended doses but can occur with prolonged intake of very high doses, typically above 10,000 IU daily for extended periods. Acute toxicity generally requires ingestion of extremely large amounts (over 50,000 IU in a single dose for adults). Symptoms of vitamin D toxicity are primarily related to hypercalcaemia and may include:
- Nausea, vomiting, and loss of appetite
- Excessive thirst (polydipsia) and frequent urination (polyuria)
- Constipation or diarrhoea
- Muscle weakness and fatigue
- Confusion, disorientation, and drowsiness
- Kidney damage (nephrocalcinosis, nephrolithiasis)
- Cardiac arrhythmias in severe cases
If you suspect a vitamin D overdose, stop taking Fultium immediately and contact your healthcare provider or emergency services. Treatment involves discontinuing vitamin D and calcium supplements, aggressive hydration, and in severe cases, administration of corticosteroids, loop diuretics, or bisphosphonates to lower serum calcium levels.
What Are the Side Effects of Fultium?
At recommended doses, Fultium is generally well tolerated with few side effects. The most common adverse effects are mild gastrointestinal symptoms. Excessive doses can cause hypercalcaemia, which may lead to more serious symptoms including kidney problems and cardiac issues.
Side effects from Fultium at standard recommended doses are uncommon. Colecalciferol has an excellent safety profile when used within established dosing guidelines. However, as with any medication, adverse effects can occur, and patients should be aware of the potential symptoms that may indicate excessive vitamin D intake.
The following frequency classification is based on regulatory submissions and post-marketing surveillance data, using the standard Medical Dictionary for Regulatory Activities (MedDRA) frequency convention:
Common (1/10 to 1/100)
May affect up to 1 in 10 people
- Hypercalcaemia (at higher doses)
- Nausea
- Abdominal pain
- Constipation
Uncommon (1/100 to 1/1,000)
May affect up to 1 in 100 people
- Hypercalciuria (excess calcium in urine)
- Flatulence
- Diarrhoea
- Metallic taste in the mouth
- Dry mouth
- Loss of appetite
Rare (less than 1/1,000)
May affect fewer than 1 in 1,000 people
- Skin rash or itching (pruritus)
- Urticaria (hives)
- Headache
- Muscle or joint pain
- Weakness and fatigue
- Nephrocalcinosis (calcium deposits in kidneys)
- Allergic reactions (very rare, may relate to excipients)
The symptoms of chronic vitamin D toxicity from sustained high-dose intake can develop gradually and may include persistent thirst, increased urination, weight loss, muscle weakness, drowsiness, and eventually renal impairment. These symptoms are associated with hypercalcaemia and typically resolve upon discontinuation of vitamin D supplementation and appropriate medical management.
It is important to distinguish between side effects from recommended doses and symptoms of toxicity from excessive intake. At doses within the established guidelines (up to 4,000 IU daily for adults), the risk of adverse effects is very low. The Endocrine Society and the IOM have both concluded that vitamin D supplementation at recommended levels carries minimal risk of harm in healthy individuals.
Seek medical advice if you experience persistent nausea, vomiting, excessive thirst, frequent urination, or constipation while taking Fultium. These symptoms may indicate elevated calcium levels (hypercalcaemia) and require blood tests to check your serum calcium and vitamin D levels. If you experience signs of an allergic reaction such as skin rash, swelling, or difficulty breathing, stop taking Fultium and seek immediate medical attention.
How Should You Store Fultium?
Store Fultium capsules below 25°C in the original packaging to protect from light and moisture. Do not use after the expiry date printed on the carton and blister strip. Keep out of the reach and sight of children.
Proper storage of Fultium is important to maintain the potency and safety of the medication throughout its shelf life. Colecalciferol can degrade when exposed to light, heat, and moisture, so appropriate storage conditions are essential.
Follow these storage guidelines for Fultium capsules:
- Temperature: Store below 25°C (77°F). Do not refrigerate or freeze, as this may affect the integrity of the soft capsule shell.
- Light protection: Keep the capsules in their original blister packaging until ready to use. Vitamin D3 is sensitive to ultraviolet light, which can cause degradation.
- Moisture: Store in a dry place. Do not store in bathrooms or other humid environments.
- Child safety: Keep all medicines out of the reach and sight of children. Consider using a locked medicine cabinet.
- Expiry date: Do not use Fultium after the expiry date stated on the packaging. The expiry date refers to the last day of that month.
- Disposal: Do not dispose of unused Fultium in household waste or via wastewater. Return any unwanted medication to a pharmacy for safe disposal in accordance with local regulations.
If the capsules appear discoloured, damaged, or if the blister packaging is compromised, do not take the medication and consult your pharmacist for a replacement. Soft capsules may become slightly softer in warmer conditions but should not be noticeably deformed or leaking.
What Does Fultium Contain?
Each Fultium soft capsule contains 400 IU (10 micrograms) of colecalciferol (vitamin D3) as the active ingredient. The capsule also contains inactive ingredients (excipients) that form the capsule shell and the oily vehicle in which the vitamin D is dissolved.
Understanding the full composition of Fultium is important, particularly for patients with known allergies or dietary restrictions. The formulation is designed to optimise the absorption and stability of colecalciferol in a convenient soft capsule format.
Active Ingredient
- Colecalciferol (Vitamin D3): 400 IU (10 micrograms) per capsule. Colecalciferol is derived from the irradiation of 7-dehydrocholesterol, typically sourced from lanolin (sheep wool grease). This is the same chemical form of vitamin D produced endogenously in human skin upon UVB exposure.
Inactive Ingredients (Excipients)
The typical excipients found in Fultium soft capsules include:
- Medium-chain triglycerides (MCT oil): An oily vehicle derived from coconut or palm kernel oil, used to dissolve the fat-soluble colecalciferol
- Gelatin: Forms the soft capsule shell (note: this makes the product unsuitable for vegetarians and vegans)
- Glycerol: A plasticiser used to keep the capsule shell flexible
- Purified water: Used in the capsule shell manufacturing process
- Butylated hydroxytoluene (BHT): An antioxidant added to prevent degradation of the colecalciferol
Some formulations of Fultium may also contain additional excipients such as dl-alpha-tocopherol (vitamin E) as a stabiliser. Patients with allergies to any of the listed ingredients should inform their healthcare provider before starting treatment. Importantly, specific Fultium formulations should be checked for the presence of peanut oil (arachis oil) or soya lecithin, as these are allergens that may be present in certain vitamin D preparations. Patients with known peanut or soya allergies should verify the specific product formulation with their pharmacist.
Fultium soft capsules contain gelatin derived from animal sources and are therefore not suitable for vegetarians or vegans. The colecalciferol in Fultium is typically derived from lanolin, an animal source. Patients who require a vegetarian or vegan vitamin D3 supplement should discuss alternatives (such as lichen-derived vitamin D3) with their healthcare provider or pharmacist.
Frequently Asked Questions About Fultium
Fultium is a prescription vitamin D3 supplement containing colecalciferol. It is primarily used to treat and prevent vitamin D deficiency, support bone health, and as an adjunct treatment for osteoporosis. Vitamin D deficiency is extremely common, affecting approximately one billion people worldwide, and can lead to weakened bones (osteomalacia in adults, rickets in children), increased risk of falls and fractures, and impaired immune function. Your doctor may prescribe Fultium if your blood tests show low vitamin D levels or if you are at risk of deficiency.
Fultium soft capsules should be swallowed whole with a glass of water, preferably with a main meal containing some dietary fat (such as lunch or dinner). Vitamin D is a fat-soluble vitamin, meaning it is absorbed much more efficiently when taken with dietary fat. Do not chew, crush, or open the capsules. Take Fultium at approximately the same time each day to help establish a consistent routine. If you forget a dose, take it as soon as you remember on the same day, but do not double the dose the following day.
Vitamin D supplementation during pregnancy is generally recommended by major health organisations including the WHO and NICE. Adequate vitamin D levels are important for fetal skeletal development and maternal bone health. However, doses should not exceed recommended amounts (typically 400–1,000 IU daily) without medical supervision, as excessive vitamin D can cause hypercalcaemia, which may potentially harm the developing baby. Always consult your obstetrician or midwife for advice on the appropriate dose during pregnancy.
At recommended doses, side effects from Fultium are uncommon. The most frequently reported effects include mild gastrointestinal symptoms such as nausea, constipation, or abdominal discomfort. Excessive doses taken over prolonged periods can lead to hypercalcaemia (abnormally high calcium levels), which may cause symptoms including excessive thirst, frequent urination, nausea, weakness, and in severe cases, kidney damage. Contact your doctor if you experience persistent gastrointestinal symptoms or any signs of an allergic reaction.
Fultium contains the same active ingredient – colecalciferol (vitamin D3) – as many over-the-counter vitamin D supplements. The key difference is that Fultium is a licensed medicinal product manufactured under strict pharmaceutical quality control standards (Good Manufacturing Practice, or GMP). This means each capsule contains a precisely measured dose that has been verified through rigorous testing. Over-the-counter supplements are classified as food supplements and may not be subject to the same stringent regulatory standards. Your doctor may prescribe Fultium when a reliable, standardised dose is clinically important.
Serum vitamin D levels typically begin to rise within 1–2 weeks of starting Fultium. However, it usually takes 6–8 weeks of consistent daily use to reach a stable plateau in blood levels of 25-hydroxyvitamin D. Your doctor may order a blood test approximately 3 months after starting treatment to check whether your vitamin D levels have reached the target range (generally above 50 nmol/L or 20 ng/mL, with some guidelines recommending levels above 75 nmol/L or 30 ng/mL). Clinical improvements in symptoms such as bone pain or muscle weakness may be noticed gradually over several weeks to months of adequate supplementation.
References
This article is based on peer-reviewed medical literature and international clinical guidelines. All medical claims follow the GRADE evidence framework with Level 1A evidence where available.
- Holick MF, et al. “Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline.” Journal of Clinical Endocrinology & Metabolism. 2011;96(7):1911–1930. doi:10.1210/jc.2011-0385
- Ross AC, et al. “The 2011 Report on Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine: What Clinicians Need to Know.” Journal of Clinical Endocrinology & Metabolism. 2011;96(1):53–58.
- National Institute for Health and Care Excellence (NICE). “Vitamin D: supplement use in specific population groups.” Public health guideline PH56. Updated 2017.
- World Health Organization. “Nutritional rickets: a review of disease burden, causes, diagnosis, prevention and treatment.” WHO, 2019.
- Bouillon R, et al. “Skeletal and Extraskeletal Actions of Vitamin D: Current Evidence and Outstanding Questions.” Endocrine Reviews. 2019;40(4):1109–1151.
- British National Formulary (BNF). “Colecalciferol.” National Institute for Health and Care Excellence. Accessed December 2025.
- European Medicines Agency (EMA). “Summary of Product Characteristics – Vitamin D preparations.” EMA, 2023.
- Martineau AR, et al. “Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.” BMJ. 2017;356:i6583.
- Bolland MJ, et al. “Effects of vitamin D supplementation on musculoskeletal health: a systematic review, meta-analysis, and trial sequential analysis.” The Lancet Diabetes & Endocrinology. 2018;6(11):847–858.
- Scientific Advisory Committee on Nutrition (SACN). “Vitamin D and Health.” Public Health England, 2016.
Medical Editorial Team
This article has been written and medically reviewed by the iMedic Medical Editorial Team, comprising licensed physicians with specialist expertise in clinical pharmacology, endocrinology, and metabolic bone disease.
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iMedic Medical Editorial Team – Specialists in clinical pharmacology and evidence-based medicine
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iMedic Medical Review Board – Independent review according to international guidelines (WHO, BNF, NICE, Endocrine Society)
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