Doctors in the US never ever prescribe herbs or supplements. On rare occasions when you have a legitimate vitamin deficiency, verified by blood work, they will prescribe medical grade vitamin tablets, from a pharmacy that has actually tested the vitamin content of the product. Vitamin D deficiency is quite common, and while rare, scurvy (vitamin C deficiency) can happen if someone is malnourished.
My doctor has told me on more that one occasion that herbal supplements are completely unregulated, many don’t contain even a bit of the claimed herb, and sometimes have legitimately harmful plants mixed in, as if someone just gathered a bunch of weeds, dried and ground them up.
Speak for yourself.