Vitamin D2 (ergocalciferol) is a form of vitamin D that's available both over the counter or with a prescription, depending on the dose. It's used to treat vitamin D deficiency (low vitamin D levels), including in various medical conditions, such as hypoparathyroidism (low parathyroid hormone) and rickets. Vitamin D2 (ergocalciferol) is taken by mouth, typically once a day (unlike vitamin D3, which can be prescribed once weekly at higher doses).
Low vitamin D, and certain related conditions:
Hypoparathyroidism (low parathyroid hormone levels)
Familial hypophosphatemia (genetic condition causing low phosphate levels)
Vitamin D-resistant rickets (weakening of the bones caused by low vitamin D)
Vitamin D2 (ergocalciferol) is a form of vitamin D that's available as a dietary supplement. Vitamin D allows your body to absorb more calcium and phosphate, which is important to keep your bones healthy and strong. If you have problems with your parathyroid gland, your body doesn't make vitamin D very well on its own. Vitamin D2 (ergocalciferol) replaces the vitamin D your parathyroid gland isn't making.
Source: DailyMed
Side effects that you should report to your care team as soon as possible:
Side effects that usually do not require medical attention (report these to your care team if they continue or are bothersome):
Taken by mouth
Available as a prescription and OTC at different doses
A good option for vegetarians and vegans, as it's plant-based
Only needs to be taken once a day
Might not raise vitamin D levels as well as cholecalciferol (Vitamin D3)
Too much vitamin D can lead to unwanted side effects
High doses might not be a good option for pregnant or nursing mothers
Requires regular blood tests
You can take vitamin D2 (ergocalciferol) with or without food at any time of the day. Taking it with a meal or right after you wake up can make it easier for you to remember. Try to take vitamin D2 (ergocalciferol) at the same time every day so the medication levels stay consistent in your body.
Don't take more vitamin D2 (ergocalciferol) than instructed by your provider, since this can lead to unwanted side effects like nausea and vomiting. Contact your provider if you notice an unexplainable loss of appetite, weight loss, weakness, general aches, or stiffness. These can be signs that your dose is too high.
Continue to take vitamin D2 (ergocalciferol) as long as your provider tells you to do so. The length of time you'll use it is different for everyone, since it depends on your condition and the results of your blood tests. Because vitamin D2 (ergocalciferol) can be used for genetic or ongoing conditions, it's possible you might need to take this medication long term or even for the rest of your life.
Be sure to get any ordered blood tests done on time, because your lab results can affect your dose.
Don't start taking other forms of vitamin D without first discussing it with your provider to avoid taking too much. This can include multivitamins and foods (like milk or orange juice) that have been fortified with vitamin D. Make sure your providers have a list of all your medications and supplements that you take on a regular basis, including the ones you purchase over the counter.
Vitamin D2 (ergocalciferol) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.
Risk factors: Rickets
Vitamin D2 (ergocalciferol) shouldn't be used if you have high levels of calcium or vitamin D in your blood. If you take more vitamin D2 (ergocalciferol) than the recommended or prescribed dose, it can cause calcium to build up in your blood. This can be dangerous for your kidneys. Because you need to take very high doses of this medication to treat rickets, it's much more likely for this to happen if you have rickets. Be sure to get all ordered blood tests done on time so your provider can make sure your vitamin D levels aren't too high and you're taking the correct dose. If you notice unexplained nausea that doesn't go away, a loss of appetite, weight loss, constipation, muscle pain, muscle stiffness, or a change in how much or how often you urinate, talk to your provider. These could be early signs that you're taking too much vitamin D and your calcium blood level is too high.
Prescription-only vitamin D2 (ergocalciferol):
Your dose can change depending on your blood vitamin D levels.
Hypoparathyroidism: The typical dose ranges between 50,000 and 200,000 units (or international units, IU) by mouth every day, along with calcium supplementation.
Vitamin D-resistant rickets: The typical dose ranges between 12,000 and 500,000 units (or IU) by mouth every day.
Familial hypophosphatemia: Ask your healthcare provider to see what dose you should take.
Please note: Vitamin D2 (ergocalciferol) is available OTC in doses below 50,000 units. Ask your healthcare provider to see what dose you should take.
High blood calcium levels
High blood vitamin D levels
Malabsorption syndrome (when your body can't absorb nutrients)
Low vitamin D, and certain related conditions:
Hypoparathyroidism (low parathyroid hormone levels)
Familial hypophosphatemia (genetic condition causing low phosphate levels)
Vitamin D-resistant rickets (weakening of the bones caused by low vitamin D)
Low calcium in people on dialysis
Secondary hyperparathyroidism in people not yet on dialysis
Low calcium in people with hypoparathyroidism or pseudohypoparathyroidism
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Alembic Pharmaceuticals Inc. (2023). ERGOCALCIFEROL capsule [package insert]. DailyMed.
Camacho, P. M., et al. (2020). American Association of Clinical Endocrinologists/ American College of Endocrinology clinical practice guidelines for the diagnosis and treatment of postmenopausal osteoporosis— 2020 update. Endocrine Practice.
Johnson, L. E. (2022). Vitamin D excess. Merck Manual.
Khundmiri, S. J., et al. (2016). PTH and Vitamin D. Comprehensive Physiology.
MedlinePlus. (2022). Hypoparathyroidism.
MedlinePlus. (2022). Pseudohypoparathyroidism.
MedlinePlus. (2022). Rickets.
National Kidney Foundation. (n.d.). Dialysis.
National Kidney Foundation. (n.d.). Secondary hyperparathyroidism.
Shieh, A., et al. (2016). Effects of high-dose vitamin D2 versus D3 on total and free 25-hydroxyvitamin D and markers of calcium balance. The Journal of Clinical Endocrinology and Metabolism.
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