Q: I have found that 5,000 micrograms of biotin daily is a miracle drug for my weak, brittle fingernails. My dermatologist recommended this.

Also, because of previous skin cancer, I wear sunscreen whenever I am outside. My family doctor told me to take 2,000 IU of vitamin D3 to get my level up to the normal range. I am a healthy, active man, so I plan to continue with my current supplements.

A: Thank you for sharing your experience with biotin, a B vitamin. The federal Office of Dietary Supplements notes that an adequate daily intake of biotin for adults is 30 mcg. It goes on to state: “Signs of biotin deficiency include skin rashes, hair loss, and brittle nails. Therefore, biotin supplements are often promoted for hair, skin, and nail health. However, these claims are supported, at best, by only a few case reports and small studies.”

Even though you are taking a high dose of biotin, this nutrient appears quite safe. That said, it can interfere with some lab tests. Biotin artificially lowers the results of TSH and 25-hydroxyvitamin D tests. If you ever need to have blood drawn, make sure the lab knows you are taking biotin.

Q: If I’m not mistaken, some over-the-counter antihistamines have anticholinergic activity. Before reading that anticholinergic drugs could be bad for the brain, I’ve taken these for sleep a few nights in a row. For several weeks afterward I experienced memory problems and migraines.

The yardman at my condo complex has been taking these drugs for years and he barely has any mind left. He can’t remember much of anything, and apparently is not aware of it because he doesn’t write things down. I believe a few customers have scolded him about this, but he apparently forgets that, too. I can hardly wait until he retires.

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A: Diphenhydramine is a sedating antihistamine that is almost always included in nighttime pain relievers. It is the “PM” in products like Advil PM, Aleve PM or Tylenol PM.

Diphenhydramine has anticholinergic activity. That means it alters the action of a brain chemical called acetylcholine, which is crucial for cognitive function and memory. Geriatricians discourage the use of anticholinergic drugs in older patients because they can contribute to impairment.

Our “Guide to Drugs and Older People” has a list of medications that may be inappropriate for seniors. Anyone who would like a copy, please send $3 in check or money order with a long (No. 10), stamped (70 cents), self-addressed envelope to: Graedons’ People’s Pharmacy, No. O-85, P.O. Box 52027, Durham, NC 27717-2027. It also can be downloaded for $2 from the Health eGuide section of our website: www.peoplespharmacy.com.

Q: Can you tell me about Repatha? Are the people who take it actually helped by it? What about side effects? Is lowering cholesterol worth the risks of taking this?

A: Evolocumab (Repatha) is an injectable medication used to lower LDL cholesterol even more than statins alone. In one major study, people taking Repatha were less likely to suffer heart attacks or strokes but no less likely to die prematurely (New England Journal of Medicine, May 4, 2017).

Upper respiratory tract infections, including flu, were reported more often by people taking Repatha. Other side effects may include sore throat, sinusitis, gastroenteritis and injection-site reactions.

You should discuss the pros and cons of this medication with your doctor. If you have heart disease and are at high risk of a heart attack or stroke, this drug might offer benefit.