Yes having unpaid medical bills that are sent to collections can negatively impact your credit score and lower your credit score substantially.
This is why it's important to have health insurance or some other type of plan to help pay the medical bills.
If not, always try to work with the hospital or other place that is billing you to make payment arrangements to pay back the medical bills that are owed.
Otherwise yes your credit score can drop a good amount for unpaid medical bills and the unpaid medical bills will affect your credit for up to 7 years.