Vitamin D2
Ergocalciferol
A form of vitamin D (vitamin D2) used to treat and prevent vitamin D deficiency.
What is Ergocalciferol?
Ergocalciferol is a form of vitamin D, known as vitamin D2, used to treat and prevent vitamin D deficiency. Vitamin D helps the body absorb calcium and keep bones, muscles and teeth healthy, and a shortage can cause bone pain, muscle weakness and, in severe cases, soft bones. Unlike the active vitamin D forms, ordinary vitamin D like this still needs the body to activate it, so it is used when the liver and kidneys are working normally. It is generally very safe, though very large amounts over a long time can raise calcium. It is often taken as a course to correct deficiency, then a smaller amount to maintain levels.
Education and reference only. This is a plain-language guide to Ergocalciferol — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Ergocalciferol is one of the ordinary forms of vitamin D, called vitamin D2, which comes from plant and yeast sources. Vitamin D is needed to absorb calcium from food and to keep bones, teeth and muscles healthy; a shortage can cause tiredness, bone and muscle aches, and in severe or long-standing cases soft, weak bones (osteomalacia in adults or rickets in children). Ergocalciferol is used to treat and prevent this deficiency. Unlike calcitriol and alfacalcidol, it is not yet activated, so the body still has to switch it on in the liver and kidneys. It is taken by mouth.
How it works
Ergocalciferol is an inactive form of vitamin D that the body converts, first in the liver and then in the kidneys, into the active form that helps the gut absorb calcium and keeps bones healthy. By topping up the body's vitamin D, it allows this natural process to work properly again, easing the bone and muscle problems of deficiency. Because the body still has to activate it, the effect is gentler and slower than the active vitamin D forms, which makes it a safe choice for ordinary deficiency when the liver and kidneys are working normally.
Company & origin
Originated / developed by: Generic (long-established).
A plant-derived form of vitamin D (vitamin D2) used in the UK to treat and prevent vitamin D deficiency.
Practical use
How to take Ergocalciferol
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth as prescribed, often as a higher-dose course first to correct deficiency, then a smaller maintenance amount.
- Follow the prescribed amount and do not add extra vitamin D from other supplements without checking, to avoid too much.
- Make sure you also get enough calcium from diet or supplements, as vitamin D and calcium work together.
- Keep to any follow-up blood tests so your levels can be rechecked after a course.
- Tell your prescriber if you have kidney problems, as the ordinary form may not be the right choice for you.
Weighing it up
Advantages & disadvantages of Ergocalciferol
Advantages
- A simple, effective and inexpensive way to treat and prevent vitamin D deficiency.
- Gentle and safe when the liver and kidneys are working normally.
- Can be given as a short higher-dose course followed by easy maintenance.
Disadvantages
- Does not work well when the kidneys cannot activate vitamin D, where active forms are needed instead.
- Very large amounts over a long time can raise blood calcium.
- Works more slowly than the active vitamin D forms, as the body must activate it first.
Practical use
Good to know
Vitamin D deficiency is common, especially in people with little sun exposure, darker skin, or who cover up, and ergocalciferol is one way to correct it. A higher-dose course is often used first to rebuild stores, followed by a smaller regular amount to keep levels up. It is generally very safe; the main caution is that very large amounts taken for a long time can raise blood calcium, so the prescribed amount should be followed and combined products checked to avoid doubling up. Vitamin D works alongside calcium, so adequate calcium intake matters too. Because it is the ordinary, unactivated form, it is not the right choice when the kidneys cannot activate vitamin D — that is where the active forms are used instead.
Who should not take it / use with caution
- People who already have high blood calcium should not take it until that is corrected.
- It is avoided in vitamin D toxicity, and the active forms are preferred when the kidneys cannot activate vitamin D.
- Used with care in conditions that raise calcium, such as some that cause too much absorption.
Monitoring
- Rechecking vitamin D levels after a treatment course where appropriate.
- Checking blood calcium if higher amounts are used or symptoms suggest it.
- Reviewing other supplements to avoid taking too much vitamin D overall.
Side effects
- Usually none at sensible amounts; vitamin D is generally well tolerated.
- Very large amounts over time can raise calcium, causing nausea, thirst, constipation or tiredness.
- Rarely, stomach upset or, in true overdose, more serious effects of high calcium.
Key interactions
- Other vitamin D-containing supplements can add up, so avoid doubling the total without advice.
- Thiazide water tablets can raise calcium when taken with vitamin D.
- Some medicines such as certain anti-epileptics and steroids can change how vitamin D works, so tell your prescriber what you take.
Available as: Tablets, capsules and oral liquid taken by mouth.
Answers
Ergocalciferol: frequently asked questions
What is ergocalciferol used for?
It is a form of vitamin D (vitamin D2) used to treat and prevent vitamin D deficiency, which helps keep bones, muscles and teeth healthy.
How is it different from calcitriol?
Ergocalciferol is the ordinary, unactivated form that the body still has to switch on, whereas calcitriol is already active and used when the body cannot do that step.
Can I take too much vitamin D?
Very large amounts over a long time can raise blood calcium, so follow the prescribed amount and avoid doubling up with other supplements.
Do I need calcium as well?
Vitamin D and calcium work together, so it helps to get enough calcium from your diet or as advised by your prescriber.
Is it suitable if I have kidney problems?
Ordinary vitamin D may not work well if the kidneys cannot activate it, so the active forms are often preferred — tell your prescriber about any kidney problems.
The wider class
About Vitamin D
Ergocalciferol belongs to the vitamin d class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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