A regular withdrawal after the refund and add/drop date results in W’s. W’s are not great to have on a transcript either, though they don’t affect a GPA. Medical withdrawals, in my experience at two schools, wipe the slate clean with no W’s. One school we have experience with doesn’t have medical withdrawals at all.
@parentologist, again, if there are 4 incompletes and the OP’s son is stressed, I think that the work would be burdensome. One course incomplete might be doable.