diff --git a/causal_testing/testing/base_test_case.py b/causal_testing/testing/base_test_case.py
index 2cc02304..8838b932 100644
--- a/causal_testing/testing/base_test_case.py
+++ b/causal_testing/testing/base_test_case.py
@@ -17,3 +17,7 @@ class BaseTestCase:
     treatment_variable: Variable
     outcome_variable: Variable
     effect: str = Effect.TOTAL.value
+
+    def __post_init__(self):
+        if self.treatment_variable == self.outcome_variable:
+            raise ValueError(f"Treatment variable {self.treatment_variable} cannot also be the outcome variable.")
diff --git a/tests/testing_tests/test_causal_test_case.py b/tests/testing_tests/test_causal_test_case.py
index 154d76e3..8e4ef8cc 100644
--- a/tests/testing_tests/test_causal_test_case.py
+++ b/tests/testing_tests/test_causal_test_case.py
@@ -98,6 +98,10 @@ def setUp(self) -> None:
     def tearDown(self) -> None:
         shutil.rmtree(self.temp_dir_path)
 
+    def test_invalid_base_test_case(self):
+        with self.assertRaises(ValueError):
+            BaseTestCase(self.A, self.A)
+
     def test_check_minimum_adjustment_set(self):
         """Check that the minimum adjustment set is correctly made"""
         minimal_adjustment_set = self.causal_dag.identification(self.base_test_case_A_C)