A lot of men who take finasteride (Propecia) to treat their male pattern baldness report experiencing brain fog. Scientists are not sure if the drug actually causes this side effect, or if it's just a coincidence that so many people experience it. Some researchers believe that the drug may cause changes in the levels of serotonin and other neurotransmitters in the brain, which could lead to the symptoms of brain fog.
If you are concerned about experiencing brain fog after taking finasteride, talk to your doctor about your options. There may be other medications available that can treat your hair loss without causing these side effects. Or, you may want to consider cancelling your prescription and finding another treatment for your baldness.