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Medicines and supplements

Calcium and lithium: what to know about blood calcium

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

Ask your pharmacist or doctor before combining. NIH lists lithium as 1 of 4 examples of medicines that interact with calcium supplements: long-term lithium use can raise blood calcium, and extra calcium could add to that risk. The lithium label asks for blood calcium to be checked regularly.1,2,3

Key facts

  • NIH names lithium, dolutegravir, levothyroxine and quinolone antibiotics as examples of medicines that calcium supplements may interact with.1
  • NIH's consumer sheet says long-term lithium use, or lithium taken together with calcium supplements, can lead to abnormally high levels of calcium in the blood.2
  • The lithium label links long-term treatment to persistent overactive parathyroid glands and high blood calcium, and tells prescribers to monitor blood calcium regularly.3
  • The label adds that high calcium may not resolve after lithium is stopped.3
  • MedlinePlus lists lithium among the medicines that can cause high blood calcium, and says most people with high calcium have no symptoms.4

Your doctor may want to check on you

Long-term lithium use can raise blood calcium, and NIH notes that taking calcium supplements with lithium could add to that risk. The lithium label asks for blood calcium to be checked regularly.1,2,3

Expected from how the two work, not shown in studies

Why do NIH and the lithium label mention calcium?

MedlinePlus describes lithium as a medicine used to treat and prevent episodes of mania in people with bipolar disorder.5

The concern is not about lithium being absorbed. It is about calcium in the blood. NIH's fact sheet for health professionals says long-term lithium use can lead to hypercalcemia, the medical word for too much calcium in the blood, and that using both lithium and calcium supplements could increase that risk. The consumer sheet gives the same message in plainer words.1,2

NIH words the added risk as something that could happen. None of the sources read for this page gives an amount of calcium at which it starts, or describes a trial of calcium supplements in people taking lithium. That is why this entry is labeled expected, not measured.1

What does the lithium label say about calcium?

Under its warnings, the label says long-term lithium treatment is associated with persistent hyperparathyroidism, which means overactive parathyroid glands, and with hypercalcemia. It says that when clinical signs of high calcium are present, stopping lithium and changing to another mood stabilizer may be necessary, and that high calcium may not clear up after lithium is stopped. It closes with a direct instruction to prescribers: monitor serum calcium regularly.3

Those are decisions for your prescriber, not for you. MedlinePlus tells people to keep taking lithium even when they feel well and not to stop without talking to their doctor. It also asks them to report the vitamins and nutritional supplements they take, because doses may need to change or monitoring may need to be closer.5

How would you know if blood calcium is too high?

High blood calcium is rare in healthy people and usually comes from conditions such as overactive parathyroid glands or cancer rather than diet. It can cause poor muscle tone, kidney problems, constipation, nausea, weight loss, tiredness, frequent urination and abnormal heart rhythms.1,2

MedlinePlus says most people with high blood calcium have no symptoms and that it is usually found on routine blood tests. When symptoms do occur, it lists nausea or vomiting, poor appetite, constipation, increased thirst or more frequent urination, muscle weakness or twitches, and tiredness or confusion.4

MedlinePlus also notes that calcium in the blood can read high when the body is low on fluids. The lithium label asks prescribers to rule out that false reading when calcium is only mildly raised. Interpreting a result is a job for your prescriber.3,4

Which everyday products contain calcium?

Multivitamins commonly contain about 200 to 300 mg of calcium. Calcium supplements, with or without vitamin D, commonly contain 500 or 600 mg.1

Calcium carbonate antacids provide about 270 to 400 mg of calcium in each chewable tablet or soft chew, depending on strength.1

The two NIH entries above show how many products carry calcium: multivitamins, supplements with or without vitamin D, and antacids. MedlinePlus lists too much vitamin D among the causes of high blood calcium, so a combined calcium and vitamin D product is worth naming to your pharmacist as well.1,4

Calcium carbonate is both a supplement form and an antacid ingredient. MedlinePlus notes that it can make other medicines less effective, which is an absorption question separate from the blood calcium concern on this page.6

What to ask your pharmacist about calcium and lithium

  • Does my lithium prescription come with regular calcium blood tests, and should I report a new supplement before the next one?
  • Do my antacids, multivitamin or calcium and vitamin D tablets count as added calcium?
  • Which symptoms of high blood calcium should make me call you?
  • Should my calcium supplement be reviewed at my next lithium blood test?

Bring every label you use. If a product lists calcium carbonate, calcium citrate or vitamin D, say so, even when it is a small part of a multivitamin.1

Questions people ask

Does lithium affect calcium levels?

Over the long term it can. The lithium label links long-term treatment to persistent high blood calcium and parathyroid changes, and it tells prescribers to monitor calcium regularly.3

What is the calcium and lithium interaction?

NIH calls it an interaction because both can raise blood calcium. It is listed as expected from how the two act, so ask your pharmacist whether it applies to you.1

Can calcium carbonate raise lithium levels?

The sources read for this page describe an effect on blood calcium, not on the level of lithium in the blood. Calcium carbonate is a common antacid and supplement form, so mention it to your pharmacist like any other calcium product.1,3

Are calcium and lithium levels checked regularly?

The label asks prescribers to monitor blood calcium regularly during lithium treatment. How often is for your prescriber to say.3

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Sources

  1. Office of Dietary Supplements, National Institutes of Health. Calcium: Fact Sheet for Health Professionals. Updated June 22, 2026. Opened 2026-10-07.
  2. Office of Dietary Supplements, National Institutes of Health. Calcium: Fact Sheet for Consumers. Updated September 14, 2023. Opened 2026-10-07.
  3. Lithium carbonate tablets and capsules: prescribing information (Hikma Pharmaceuticals USA). DailyMed, U.S. National Library of Medicine. Effective August 16, 2026. Opened 2026-10-07.
  4. MedlinePlus Medical Encyclopedia. Hypercalcemia. Review date January 25, 2026. Opened 2026-10-11.
  5. MedlinePlus, U.S. National Library of Medicine. Lithium: MedlinePlus Drug Information. Last revised April 15, 2017. Opened 2026-10-11.
  6. MedlinePlus, U.S. National Library of Medicine. Calcium Carbonate: MedlinePlus Drug Information. Last revised June 20, 2024. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.