How your income from the clinical studies should be reported depends on whether or not your participation in the clinical studies is just occasional or if it occurs on a regular basis.
[Revenue rulings (58-112, 55-431 and 55-258) indicate that income from an occasional act or transaction, absent proof of efforts to continue those acts or transactions on a regular basis, are not income from a trade or business.]
If participating in clinical studies is not something you do on a recurring and regular basis, the income can be reported as "other income" and you will not be subject to self-employment tax on it.
However, keep in mind, there is a trade-off associated with reporting your 1099 income from the clinical studies as "other income" instead of "self-employment income. While you will not have to pay self-employment tax on the income, it will no longer qualify as "earned income" for the purposes of the Earned Income Credit (EIC) or any other tax benefit that is dependent on earned income such as an IRA deduction.
If after reading the above, you decide that you want to amend your return to change the income from "self-employment income" to "other income", please follow these instructions: How to Change a Tax Return You Already Filed.
