Hi, I have been living in US for past 6 years. I just started my postdoc on OPT. I have been deducted the social security and medicare charges from my pay checks. I am wondering if I can get these charges reimbursed while filing the tax return?
Additionally, out of my paycheck of 3400, I am left with only 2300. They are charging 750 dollars in state and federal taxes and 90 in medicare/social security. Isn't it too much?

Since you are on OPT, you are on a stude nt visa, either F-1 or J-1, which normally has a FIVE-year time limit on it for FICA tax exemption. Hence, in the SIXTH year, you ARE liable for FICA (Social Security and Medicare) taxes. This is NOT governed by tax treaty, but rather is a matter of U.S. tax law.

The taxes withheld for Social Security is based on a flat 4.2%; Medicare is taxed at 1.45%.

The withholding for federal and state income taxes appears to be accurate.