Do you have a full (NOT a training) license? It can sometimes be hard for J1’ers to obtain while in training which is why I ask. If you don’t, then the answer is almost certainly “No” as you need a supervising physician, and working that out at a free clinic outside of your program would be hard.
If you do have a full license then you probably can, but look very closely at your residency contract. Some (like mine when i was in training) stipulated no clinical work was to be done outside of the program (“no moonlighting”) - I know of people fired for repeated violation of this policy.
