| Country | Abbreviations | Source Register | Number |
| United States of America | US | ClinicalTrials.gov | 102,634 |
| Japan | JP | JPRN | 16,453 |
| EU | EU | EU Clinical Trials Register | 8729 |
| Iran | IR | IRCT | 8532 |
| Australia/New Zealand | AU/NZ | ANZCTR | 6596 |
| China | CH | ChiCTR | 6458 |
| India | IN | CTRI | 4723 |
| United Kingdom | UK | ISRCTN | 4469 |
| Germany | DE | German Clinical Trials Register | 2952 |
| Netherland | NE | Netherlands Trial Register | 2835 |
| Korea | KR | CRIS | 1531 |
| Brazil | BR | REBEC | 697 |
| Thai | TH | TCTR | 587 |
| Pan Africa | - | PACTR | 567 |
| Sri Lanka | LK | SLCTR | 129 |
| Cuba | CU | RPCEC | 109 |