diff --git a/fastapi/_compat/shared.py b/fastapi/_compat/shared.py
index 005ba67040..bfa5296dcb 100644
--- a/fastapi/_compat/shared.py
+++ b/fastapi/_compat/shared.py
@@ -21,7 +21,7 @@ from fastapi.types import UnionType
 from pydantic import BaseModel
 from pydantic.version import VERSION as PYDANTIC_VERSION
 from starlette.datastructures import UploadFile
-from typing_extensions import get_args, get_origin
+from typing_extensions import Annotated, get_args, get_origin
 
 # Copy from Pydantic v2, compatible with v1
 if sys.version_info < (3, 10):
@@ -103,6 +103,9 @@ def field_annotation_is_complex(annotation: Union[Type[Any], None]) -> bool:
     if origin is Union or origin is UnionType:
         return any(field_annotation_is_complex(arg) for arg in get_args(annotation))
 
+    if origin is Annotated:
+        return field_annotation_is_complex(get_args(annotation)[0])
+
     return (
         _annotation_is_complex(annotation)
         or _annotation_is_complex(origin)
diff --git a/fastapi/_compat/v2.py b/fastapi/_compat/v2.py
index eb5543fc99..8784d5afcd 100644
--- a/fastapi/_compat/v2.py
+++ b/fastapi/_compat/v2.py
@@ -1,4 +1,5 @@
 import re
+import warnings
 from copy import copy, deepcopy
 from dataclasses import dataclass
 from enum import Enum
@@ -82,9 +83,20 @@ class ModelField:
         return self.field_info.annotation
 
     def __post_init__(self) -> None:
-        self._type_adapter: TypeAdapter[Any] = TypeAdapter(
-            Annotated[self.field_info.annotation, self.field_info]
-        )
+        with warnings.catch_warnings():
+            # Pydantic >= 2.12.0 warns about field specific metadata that is unused
+            # (e.g. `TypeAdapter(Annotated[int, Field(alias='b')])`). In some cases, we
+            # end up building the type adapter from a model field annotation so we
+            # need to ignore the warning:
+            if shared.PYDANTIC_VERSION_MINOR_TUPLE >= (2, 12):
+                from pydantic.warnings import UnsupportedFieldAttributeWarning
+
+                warnings.simplefilter(
+                    "ignore", category=UnsupportedFieldAttributeWarning
+                )
+            self._type_adapter: TypeAdapter[Any] = TypeAdapter(
+                Annotated[self.field_info.annotation, self.field_info]
+            )
 
     def get_default(self) -> Any:
         if self.field_info.is_required():