Dear Dr Rassman,
According a study done on behalf of Merck, patients treated with 0.2 mg finasteride showed approximately an increase of 61 hairs versus an increase of 77 hairs in 1 inch square treated with 1 mg of finasteride over the 6 month period. So can we say that taking 0.5 mg of finasteride may yield nearly the same results with 1 mg treatment
You are correct. We have known about this for many years (and have reported it here), though the standard dose is 1mg. For those who have unwanted side effects, taking 1/2 of the standard dose of Propecia should be considered, which we have been advising for many years.* Some of the original studies suggest that 1/2 the dose can be 80% as effective as the full dose and 1/4 of the dose could be half as effective as the full dose.
The original Merck study wanted to know the best and most effective dose, and the statistical data suggested 1mg. This was across a large population and if you assume that there is a bell curve, there is a wide range of responses. That also may mean that as many people as impacted by 1/2 the dose with 80% effectiveness, one might see that a sizable proportion of the population may require a higher dose than 1mg. When we see the response fall off, or a poor response, we are now recommending doubling the dose provided that the side effects do not appear.
*As always, discuss any changes to your prescription medication dosing with your prescribing doctor.