I have never known of any doctor that prescribed good quality vitamins. They prescribe what the drug companies tell them about and usually the vitamins manufactured by giant pharm companies are poor quality. The fact that Merck doesn't tell you if it's d-tocopherol or dl-tocopherol (synthetic) is of some concern. It is also not a tocopherol complex. The label should look something like this.
Vitamin E 400 IU 1,333%
(as d-Alpha Tocopherol plus d-Beta, d-Gamma,
d-Delta Tocopherols)