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Vitamin D3 is one of the most popular vitamins in the pharmacy these days. That’s because a lot of people are low in vitamin D. Vitamin D3 is often considered to be the best supplement to replenish low nutrient levels. But did you know that too much vitamin D3 can pose problems? Until we received this question, we had not realized vitamin D3 had been used as a mouse and rat poison!

D-Con and Vitamin D3:

Q. I had a little mouse problem, so I went to buy some mouse poison. The first brand I bought turned out to contain a nerve toxin. I didn’t want to mess with that, so I returned it and searched for D-Con.

I’d always heard D-Con used a potent blood thinner called warfarin. I was surprised to find that D-Con now contains cholecalciferol, Vitamin D3, instead. How does that work?

What’s in Mouse and Rat Poison?

A. Many rodenticides (mouse and rat poison) used to contain anticoagulants like warfarin. This drug works by causing internal bleeding. Warfarin is still used in human medicine in carefully monitored doses to prevent blood clots.

While some rodenticides may still contain warfarin, there are now other options. Bromethalin is a neurotoxin that leads to paralysis. This chemical can be very dangerous for pets. Cats may be especially vulnerable to bromethalin. Anyone who uses a mouse and rat poison must pet proof the house!

Vitamin D3 as a Mouse and Rat Poison

Cholecalciferol (vitamin D3) has been used for decades. It is considered a safe dietary supplement for humans.

At high doses this hormone causes blood calcium to rise to toxic levels. This in turn leads to kidney damage, bleeding and heart problems. This mouse and rat poison is also toxic to pets and must be kept well out of their reach.

As with all poisons, the dose is critical. That is why the tolerable upper limit is set at 4,000 IUs for adult humans. Some people believe that if a little is good then a lot is better. Anyone who uses a lot more than 4,000 IU daily should monitor blood levels of 25-hydroxy vitamin D regularly. If this fat soluble vitamin builds up in the body to toxic levels it could lead to hypercalcemia (excessive levels of calcium in the bloodstream). Symptoms can include muscle pain and/or weakness.

Too Much Vitamin D?

Here is an article and reader stories that point out the problems with too much vitamin D:

Too Much Vitamin D Resulted in Lingering Leg Pain

Too Much Vitamin D Resulted in Lingering Leg Pain

Kass in N.J. attributes her pain to vitamin D3:

“I have started taking D3 for the past week. I have increased pain in my legs and knees and my feet have swelled up. the fatigue is awful. Today I stopped taking it and hopefully in a few days I will have less pain. Who would think a vitamin would do this :(“

Eliza in South Australia shared a somewhat similar reaction to a BIG dose:

“I was diagnosed with Hashimoto’s a decade ago; my then doc prescribed 100,000iU of vit D (in oil) per week after test results. (47nmol/L when the desirable range os 60-160).

“Soon after taking the first dose, my calves cramped up badly during a regular beach walk and stayed painful. Neither the doc nor the compounding pharmacy could explain it at the time.”

Deb in Kailua, Kona shared another story:

“The same thing happened to me. I had terrible bone pain in my knees and legs when I upped my vitamin D3 to 5000. I got terribly constipated. I have tried to take vitamin D3 over the years and each time it happened and I had to quit. My level is at 48 so I think I’m going to quit trying to take it, it’s not worth the pain. Does this pain come from the calcium being leached from the bones or?”

Learn More About Vitamin D:

You can learn more about vitamin D in our Guide to Vitamin D Deficiency.

Share your own story about vitamin D in the comment section below.

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  1. Hugh Nile

    Well, I have taken about 11,000 IU of D3/ day for the last 10 years which keeps the blood levels (D, 25-Hydroxy) in the range that I want 50–70 ng/mL (61.7 on the last blood work). I had my first D blood test when I was taking 2,000/day and the D, 25 was only 18 ng/mL–abysmally low. I kept adding until I got it into the rang that I wanted.

    A few points: 1. It appears that if you are taking substantial amounts of D then you should also be taking K (I take LEF Super K–K1 1500 mcg, K2 1100 mcg). It appears that K is necessary to keep Calcium from depositing in the soft tissue rather than in the bone.

    2. It is absurd that many doctors prescribe 50,000–100,000 IU at one time/week. This just results in spikes in the blood levels and results in constipation etc. I take the D (as cholecalciferol) in 5,000 IU capsule–one in the morning and one in the evening (the remainder is in multi vitamin).

    3. During the 40 years before I started the 11K regime I had sinusitis multiple times/year and this usually resulted in one or two bouts of bronchitis/year. Since I started the 11K of D I have had no sinusitis and no bronchitis. Coincidence? Maybe, but I doubt it.

    4. I have also found that the “winter depression” also went away.

  2. Cindy
    Roanoke, VA

    People with pets, please be aware that rats and mice will move the pellets, possibly where pets could have access. Also, if the pets kill the rodents (or find them dead) and eat them, especially if they ingest stomach contents that may contain the toxin, they can be poisoned as well. There are currently no antidotes. At least with the warfarin/anticoagulant poisons, we have treatment options (active Vit K) if caught in time. With the the Vit D and neuro-toxins, there is currently no effective treatment. Same for children…

  3. Jen

    I took 5,000 mg a day of D3 after I was diagnosed with Hashimitos. After a year, I was having much hair loss. My doctor did blood work for D levels. My levels were way too high. I was then to take 5,000 mg every other day. Hair loss stopped. It took months. (At the time I had no idea you could take too much D3.) This was before internet. Lesson learned.

  4. mary lou W.

    been taking vit D3, 5,000 IU for over 20 years, tests consistently put my levels in the upper range of normal. In terms of leg cramps, etc. my history has been: Without extra magnesium with my multiple vitamins I come roaring up out of a deep sleep with terrible muscle cramps in calves, toes, etc. If I take the extra magnesium this never happens. I’ve gone on vacations, forgotten to bring its, and within a day or twoIi’m hit with cramps. I take magnesium pills, and within a day and half no more cramps. Have done this 4 or 5 times over the last 40 years with consistent results. Maybe the cramping etc., is due to low magnesium levels? Research is so frustrating when it uses a tunnel vision approach to a person’s cause and effect of symptoms! It really hurts people’s health in so many ways.

  5. Conrad
    West Allis WI

    In 2018, I wrote about my use of high doses of vitamin D3 in the quarterly Keep Hope Alive journal. I used 10,000 i.u. of synthetic vitamin D3 for 3 years and ended me up in the emergency room of local hospital. I also developed a sore left knee and had extremely high blood pressure.

    I have learned from research published at the Weston A Price FDN that (synthetic) vitamin D3 sold as a dietary supplement is missing a sulfate molecule that occurs naturally when UVB rays for the sun interact with cholesterol sulfate in the skin to begin the process of making pre vitamin D that is modified in the liver and finalized in the kidneys. I have quit vitamin D3 completely and get my natural vitamin D from fermented Cod liver oil. I also expose my skin to sunshine and indoor tanning beds to produce natural vitamin D the way nature intended.

    After several months of making these changes last year, all my leg and knee pain is gone and my blood pressure is down. My energy level is way up and I sleep much better.

    To reverse the damage caused by calcification to my blood vessels, I take natural vitamin K2 – 100 mcg daily. Published studies shows that K2 given to lab rats took 3 years to completely clear the calcium buildup caused by D3. Vitamin K2 is a life saver and an antidote for D3 toxicity.

  6. Al
    Tinton Falls, NJ

    Can excessive vitamin D3 (10,000mg+) ingestion over a prolonged period of time (years) lead to hardening of the arteries?

    Thank you for your kind consideration of this question. And thank you for this very informative and helpful website.

    Best regards

  7. Nancy B.

    Many of the side effects of unopposed vitamin D3 come because it can cause an exacerbation of already existing vitamin K2-7. Large doses of vitamin D can cause all kinds of calcium related side effects as the calcium cannot be deposited in the bones without the vitamin k2 transport system. Thus, people end up with calcium in the soft tissues, including the arteries.

  8. Michael

    Our multivitamin contains 4000IU of D3. In the winter months, we add 5000IU. No problems/pain encountered. Blood tests in the normal range twice annually for both of us.

  9. JB

    I wish the article submitters would include more information. For instance, at 100,000 for Hashimoto’s, what happened to the Hashimoto’s symptoms? Why did the doctor prescribe so much in one dose when it has been shown in numerous studies that smaller daily doses are more effective than 1 large weekly dose for the studied situations? Was it a gelcap, dry D3, sublingual, or a D3 skin patch? Was the source from fish, sheep lanolin, or lichen? Did the patient dose down to 50,000 once or twice a week, or 5,000 daily, and what was the result? If leg cramps “stayed painful”, how long did they have them? An hour, a few hours, overnight, 2 days? Did it resolve and/or how quickly did it resolve?

    I think it’s fairly common knowledge now that there are nutritional cofactors to vitamin D3 that must be part of one’s nutrition for the body to make the most of the D3, maybe so that it doesn’t stay in the blood but is taken in by the tissues and organs that need it. (like thyroid hormones) Are those nutritional factors absent in people who have trouble with vitamin D3? For instance, I’ve read magnesium is necessary for the body’s appropriate use of D3, and that much of our population is magnesium deficient. Could D3 bind to what little magnesium is present in magnesium-deficient people for uptake reasons, and result in cramping? (doesn’t magnesium generally relaxes muscles or affect nerve transmission? if so, if it gets used for something else, like mitigating the absorption of a high dose of D3, I could see how it might conceivably result in temporary muscle cramping or pain. But then I would think the D3 was not the source of the problem, but rather revealed a possible underlying magnesium deficiency which might need to be rectified prior to using D3 at the levels mentioned.)

  10. Cleo

    I lacked ambition and felt lethargic most the time so Doc tested me for “D” and it was 18. Told me to get on track with some 2000IU. Three mos. latter I got to 24 then I got into some powder D at local grocery and after 3 mos. of that got to 40!! Been on that for a couple yrs. but now tested 24 again. Ca level is good in middle of the range. Yes, we make little peanut butter sandwiches loaded with Vit. D for the rats and takes care of the problem almost immediately.

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