I am on ssidi and the medical study income is my only income is it also taxable, I thought it was a combination reimbursement for time and travel
Income earned performing a medical study is taxable. It is not "earned income" (income earned from performing work or services) but it must be reported as taxable income. If more than $600, the payer should give you a form 1099-MISC. It may come in the mail and they have until January 31, 2021 to mail them out. You should not get a 1099-NEC. If you get a 1099-NEC, write back for more information on how to avoid the self-employment tax.
In the past, you may have been able to deduct mileage, but not after tax reform. You can't deduct anything for your time, that's why you are being paid.