Almost all hair thinning in woman is caused by some form of medication. There are products that will help, but you need to use them regularly. Once you stop your hair will thin out again. They are not cheap either and they should not be used if you are pregnant.
The Nioxen are the best for woman with thinning hair. They cleanse the hair of chemicals. The is a 3-step program, a cleanser, a conditioner and a treatment.
These products can be found in most beauty salons and some drug stores.