You have an abundant number of hair strands, but each hair strand is thin. That's what having thick thin hair means.

In any case, medications work differently with all individuals.
As robert y said, you can try taking it to see its effect. But then, if you think that your thinning hair doesn't really bother you, I don't find any reason why you need to take them, unless of course, she prescribed it for your scalp problem, which I don't think is the case.
Hope this helps.