A drug developed for treatment of high blood pressure turns out to grow hair on bald heads, a drug company has discovered, and thought it is not available to the public as a hair restorer -- and may never be -- the company's phone is ringing off the hook. Hair growth is an unexpected side effect of a prescription drug call minoxidil which is produced by Upjohn Co. In some cases, it has even reversed typical hereditary male-pattern baldness. Upjohn is uptight about minoxidil and would prefer to discourage publicity for fear of raising false hopes. But Upjohn isn't stupid either. A spokesman confirmed that the company plans extensive testing to determine if minoxidil can be developed as a commercial product for both male and female hair-loss victims. One experiment already has been conducted on volunteer convicts, with "inconclusive" but tantalizing results. The spokesman said: "Monoxidil is the generic term for the drug. Our patented trade name for it is Loniten. After roughly a 20-year development process, it was approved by the Food and Drug Administration late in 1979 for treatment of very severy high blood pressure. "During the course of that development, one of the side effects noted was hirsutism -- which is hair growth. Hirsutism does not occur in all cases with patients on the drug. It does occur in a fairly significant number. But we cannot predict which patients will have hair growth, or where the hair will grow. "For patients who take the drug orally for high blood pressure, in a pill, the hair might appear anywhere on the body. But most commonly it will appear on the face: on the forehead, the cheeks, the mustache area -- or the scalp.

Upjohn is now trying to develop a topical solution that can be applied directly th bald or balding scalps -- in sufficient strength to stimulate hair growth there without also lowering blood pressure by absorption through the skin. The company conducted a prelimiary experiment two years ago on some 40 inmates of the state prision at Jackson, Mich. It used solutions of vary strength, testing both for effectiveness and safety. The results officially are described as inconclusive. But that is mainly because hair grows slowly -- and the experiment lasted only 14 weeks. The data the researchers did get were "interesting enough" to make it worthwhile for Upjohn to continue the research. Upjohn is now conducting further experiments that will mainly involve topical treatment for longer periods of time.