Biotin, or vitamin B7, is a water-soluble vitamin that typically causes no side effects, even in those who take it in high doses. Those who do experience side effects most often report cystic acne breakouts that clear up when they stop taking the supplement. Certain people also have allergic reactions to it, and taking it with certain medications can make them less effective. Pregnant women should not take biotin without consulting a healthcare professional because of a very low possibility of miscarriage.
The most common biotin side effect is breakouts of cystic acne along the jawline and chin. It's not clear why this happens, but many cases subside after a few weeks, and almost all stop after a person stops taking the supplement. Lowering the dosage to 2,500 mcg or less per day can help decrease this effect, as can drinking lots of water. Different people experience different frequencies of acne with the vitamin, so preventing the problem may involve trial and error to find the right dosage.
Allergic reactions are another of the potential, if uncommon, biotin side effects. Many people who do have allergies to this supplement are also allergic to cobalt and cobalamin (vitamin B12), though this is not always the case. The most common symptoms of a reaction to vitamin B7 are tightness and pain in the chest, swelling in the face and throat, nausea, and an itchy rash. Anyone with these symptoms should seek medical attention immediately, as this type of reaction can be fatal.
Several studies have shown that high doses of biotin given to pregnant rats may increase their risk of miscarriage. It's not clear why this happens, though, or whether it would have the same effect on humans. To be on the safe side, pregnant women should not take B7 supplements without talking to their medical provider first.
Biotin also interacts with some anti-seizure medications and drugs to reduce cholesterol, making them less effective. Additionally, it helps the metabolism, including regulating blood sugar levels and carbohydrate functions, which means that it can have an effect on blood glucose levels when taken in high doses. People taking anticonvulsants, cholesterol-lowering medications, or those with insulin sensitivity or diabetes should consult a medical professional before taking biotin to avoid any potential interactions.
Life-threatening interactions with this substance are extremely rare. The only recorded case is of a woman who experienced a life-threatening lung and chest condition called eosinophilic pleuropericardial effusion after she ingested a large amount of vitamin B7 along with vitamin B5. She recovered once she stopped using both vitamins. It is not known whether her condition stemmed from biotin side effects, vitamin B5 side effects, a combination of the two, or something else.
People can greatly reduce their chance of biotin side effects by taking supplements in the recommended dosage, which is generally around 30 mcg/day for adults and between 5 and 10 mcg for infants and children. Since it's water-soluble, drinking more fluids can also help flush any extra B7 out of the body. Other people prefer to avoid taking biotin in supplement form altogether and get theirs from dairy products, nuts, salmon, and whole grain products.