Doctors have known for a long time that Nizoral shampoo, in prescription and non-prescription strength, works well for controlling dandruff. But at last year´s meeting of the American Academy of Dermatology, a group of scientists suggested that over-the-counter Nizoral might also be useful as a hair loss remedy. The researchers compared Nizoral A-D Shampoo, containing 1% ketoconazole (the active ingredient), to another shampoo containing 1% zinc pyrithione. Zinc pyrithione is the active ingredient in dandruff shampoos such as Head & Shoulders.

They found that Nizoral increased hair thickness and decreased hair shedding, whereas the zinc pyrithione shampoo had the opposite effect. Their presentation didn´t make a big splash then, and it has faded into obscurity since. That´s probably because what they presented were the results of a preliminary study--the results have not yet been duplicated in other studies by other researchers--and perhaps because the scientists who did the research were under the employ of McNeil pharmaceuticals, the company that makes Nizoral.

Still, it´s not all flimflam. The study met the basic standards of good research: It was a randomized, double-blinded study. That means the researchers used a random process to decide who would use Nizoral and who would use the zinc pyrithione shampoo. Also, the study participants didn´t know which shampoo they were using, and neither did the researchers, until the results were in. Both of these measures are important in conducting a scientific study because they help eliminate any bias the researcher s or the study participants may have, which could skew the results.

Here is how the study was done:

Forty-four men with "mild to moderate dandruff and somewhat oily scalp" used Nizoral A-D Shampoo two or three times a week for six months, and 43 men with the same scalp problems used a dandruff shampoo containing zinc pyrithione just as frequently over the same period of time. Both shampoos had the same percentage (1%) of the active ingredient in them.

At the beginning of the study, the researchers looked at the health of the men´s hair and scalp. They counted the number of hairs growing on the scalp. They also measured the diameter of the hairs, and how many hairs fell out over a 24-hour period. They took these measurements again one month into the study, then again at three months, and one last time at six months.

The researchers found that the men using Nizoral had about an 8% increase in the thickness of their hair. The men using the zinc pyrithione shampoo had no such increase. In fact, their hair decreased in thickness by about 2%. The men who used Nizoral also shed fewer hairs over a 24-hour period than the zinc pyrithione shampoo users did. The Nizoral users shed about 16% fewer hairs, whereas the zinc pyrithione users shed about 6% fewer hairs.

The Nizoral users, however, had fewer hairs growing on the scalp at the end of six months than the zinc pyrithione users did. That means fewer of their hair follicles were in "anagen phase."

Not all the hair on your head grows at once. At any given time, some hair follicles are dormant, while others are actively pushing out hair: They´re in the anagen phase, which lasts about two to six years. After a short transitional phase, the dormant phase, or "telogen" phase begins, lasting about five to six weeks. When a follicle goes back into anagen phase, the hair that had been growing from it falls out, and a new hair begins to grow.

In the study, both the Nizoral users and the zinc pyrithione users had an increase in the number of hairs in anagen phase. The Nizoral group had about 6% more, whereas the zinc pyrithione had about 8% more.

These results may seem to prove that Nizoral A-D works against hair loss, but they really don´t: They merely suggest it. Scientists might be able to get a better idea of how well Nizoral works as a hair-loss remedy if they were to do a placebo-controlled study. That means one group of people would use Nizoral A-D, while another group would use a shampoo that contains no medicine at all.

One 1998 study showed that prescription-strength Nizoral, which contains 2% ketoconazole, worked just as well as minoxidil (brand name Rogaine) in men with androgenic alopecia (male hereditary balding). Both medicines increased hair thickness and increased the number of anagen-phase hair follicles on the scalp. But the researchers were guarded about the meaning of these results, saying that more rigorous studies on larger groups of men should be done.

The most certain results come from placebo-controlled studies done in more than one place, on groups of people that fit a wider profile (not just men with dandruff, in the case of the Nizoral A-D study). This is what´s known as the "gold standard" for medical research--in scientific terms, a randomized, double-blinded, placebo-controlled, multicenter study. This is the kind of study that the US Food and Drug Administration wants to see before it will approve a medicine for a particular use.