My Son Started Taking 25 Mg Of Zoloft In 8th

my son started taking 25 mg of zoloft in 8th grade from panic attacks. He is not a junior in high school and says that he is really struggling with focusing on his school work because he feels that he is anxious. I am nervous about increasing his dose to 50 mg. Do you think I should take him off the zoloft? He did not have any side effects on the 25 mg but could they come with the 50 mg. He is a 6'4 gentle giant.