Jacek Zajac, M.D.
NPI 1396817912ActiveIndividual· Internal Medicine, Endocrinology, Diabetes & Metabolism· Lombard, IL
Internal Medicine, Endocrinology, Diabetes & Metabolism (M.D.) with Endocrinology Associates SC, practicing in Lombard, Illinois. Their prescriptions cost Medicare Part D more than their services did: $2,090,805 for 6,334 claims, against $102,149 paid for services in 2024. Lilly USA, LLC was the largest of 30 companies reporting payments in 2025, $3,697 in all, mostly food and beverage. Lists Advocate Good Samaritan Hospital and 4 other hospitals as hospital affiliations.
Overview
| NPI | 1396817912 |
|---|---|
| Status | Active |
| Entity type | Individual |
| Credential | M.D. |
| Sole proprietor | No |
| NPI issued | Nov 15, 2006 |
| Last updated in NPPES | Feb 20, 2024 |
| Certified by provider | Feb 20, 2024 |
Specialties and licenses
| Taxonomy | Code | License | State |
|---|---|---|---|
| Internal Medicine, Endocrinology, Diabetes & Metabolism Primary | 207RE0101X | 361-07774 | IL |
Exclusion screening
| List | Result | Details |
|---|---|---|
| HHS-OIG LEIE · Nov 10, 2026 | No match | Checked by NPI and by name + state |
| North Carolina Medicaid · Nov 11, 2026 | No match | — |
| New York OMIG · Nov 11, 2026 | No match | — |
| Ohio Medicaid · Nov 11, 2026 | No match | — |
| Pennsylvania Medicheck · Nov 11, 2026 | No match | — |
| Washington HCA · Nov 11, 2026 | No match | — |
Official OIG search · How matching works ·Bulk check a roster
Medicare
| Enrollment (PECOS) | Enrolled Practitioner - Endocrinology (IL) |
|---|---|
| Accepts assignment | Yes (participating) |
Medicare services in 2024
| Medicare patients | 444 |
|---|---|
| Services billed | 1,206 across 15 procedure codes |
| Paid by Medicare | $102,149 |
Part D prescriptions in 2024
| Prescriptions (claims) | 6,334 · 13,513 30-day fills |
|---|---|
| Patients | 591 |
| Total drug cost | $2,090,805 |
| Generic share | 56% of claims |
Education and affiliations
| Graduation year | 1991 |
|---|---|
| Medicare specialty | Endocrinology |
Medical group
- Endocrinology Associates SCElmhurst, IL · 2 clinicians
Hospital affiliations
- Advocate Good Samaritan HospitalDowners Grove, IL
- Advocate Illinois Masonic Medical CenterChicago, IL
- Advocate Lutheran General HospitalPark Ridge, IL
- Edward HospitalNaperville, IL
- Elmhurst Memorial HospitalElmhurst, IL
Other facilities
- Residential Home HealthHome health agency · Lisle, IL
Industry payments (Open Payments)
- 2025$3,697 · 183 payments from 30 companies
- 2024$4,453 · 224 payments from 32 companies
Top paying companies in 2025
| Company | Amount | Payments |
|---|---|---|
| Lilly USA, LLC | $423.45 | 25 |
| Bayer Healthcare Pharmaceuticals Inc. | $353.64 | 16 |
| Xeris Pharmaceuticals, Inc. | $323.84 | 16 |
| Corcept Therapeutics | $255.10 | 13 |
| Novo Nordisk Inc | $240.24 | 10 |
What the 2025 payments were for
- Food and Beverage$3,635 · 181 payments
- Education$62.72 · 2 payments
Receiving payments does not imply wrongdoing. What Open Payments covers ·original records
Other endocrinologists in Lombard
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