diff --git a/src/raven_python/analysis/sampling.py b/src/raven_python/analysis/sampling.py
index e187ffd..5d11054 100644
--- a/src/raven_python/analysis/sampling.py
+++ b/src/raven_python/analysis/sampling.py
@@ -38,6 +38,7 @@
 import pandas as pd
 from cobra.exceptions import OptimizationError
 from cobra.flux_analysis import flux_variability_analysis, pfba
+from optlang.symbolics import add
 
 logger = logging.getLogger(__name__)
 
@@ -186,7 +187,9 @@ def random_sampling(
             weights = rng.random(n_objectives) * signs
             terms = [w * good_rxn_objs[j].flux_expression
                      for j, w in zip(chosen, weights, strict=True)]
-            model.objective = model.problem.Objective(sum(terms), direction="max")
+            # add() (not sum()) builds the symbolic objective in one pass; sum()
+            # re-canonicalises the optlang expression on every term (O(n^2)).
+            model.objective = model.problem.Objective(add(terms), direction="max")
             sol = model.optimize()
             if sol.status == "optimal" and abs(sol.objective_value) > 1e-8:
                 fluxes = (pfba(model) if min_flux else sol).fluxes.reindex(reaction_ids)
diff --git a/src/raven_python/manipulation/add.py b/src/raven_python/manipulation/add.py
index d772acd..4adb2e7 100644
--- a/src/raven_python/manipulation/add.py
+++ b/src/raven_python/manipulation/add.py
@@ -97,8 +97,24 @@ def _new_met_id(model: cobra.Model, prefix: str) -> str:
     return f"{prefix}{n}"
 
 
+def _build_met_index(model: cobra.Model) -> dict[tuple[str, str | None], Metabolite]:
+    """Build a ``(name, compartment) -> metabolite`` index (first match wins,
+    mirroring the old linear scan). Lets name / name[comp] resolution be O(1)
+    instead of re-scanning ``model.metabolites`` per token; callers update it as
+    new mets are created so later tokens dedup against earlier ones."""
+    index: dict[tuple[str, str | None], Metabolite] = {}
+    for met in model.metabolites:
+        index.setdefault((met.name, met.compartment), met)
+    return index
+
+
 def _try_existing(
-    model: cobra.Model, token: str, *, mets_by: str, compartment: str | None
+    model: cobra.Model,
+    token: str,
+    *,
+    mets_by: str,
+    compartment: str | None,
+    met_index: dict[tuple[str, str | None], Metabolite],
 ) -> Metabolite | None:
     """Look up ``token`` as an existing metabolite (no creation, no side effects).
 
@@ -113,10 +129,7 @@ def _try_existing(
     target_comp = comp if comp is not None else compartment
     if target_comp is None:
         return None
-    for met in model.metabolites:
-        if met.name == name and met.compartment == target_comp:
-            return met
-    return None
+    return met_index.get((name, target_comp))
 
 
 def _resolve_metabolite(
@@ -127,6 +140,7 @@ def _resolve_metabolite(
     compartment: str | None,
     allow_new_mets: bool,
     new_met_prefix: str,
+    met_index: dict[tuple[str, str | None], Metabolite],
 ) -> Metabolite:
     """Resolve an equation token to an existing or newly created Metabolite."""
     name, comp = parse_name_comp(token)
@@ -146,6 +160,7 @@ def _resolve_metabolite(
         _warn_unknown_compartment(model, compartment, token)
         met = Metabolite(token, compartment=compartment)
         model.add_metabolites([met])
+        met_index.setdefault((met.name, met.compartment), met)
         return met
 
     # name-based (mets_by="name") or explicit name[comp]
@@ -158,13 +173,9 @@ def _resolve_metabolite(
     if comp is not None and target_comp not in model.compartments and not allow_new_mets:
         raise ValueError(f"Compartment {target_comp!r} is not in the model.")
 
-    matches = [
-        met
-        for met in model.metabolites
-        if met.name == name and met.compartment == target_comp
-    ]
-    if matches:
-        return matches[0]
+    existing = met_index.get((name, target_comp))
+    if existing is not None:
+        return existing
     if not allow_new_mets:
         raise ValueError(
             f"No metabolite named {name!r} in compartment {target_comp!r}; "
@@ -173,6 +184,7 @@ def _resolve_metabolite(
     _warn_unknown_compartment(model, target_comp, name)
     met = Metabolite(_new_met_id(model, new_met_prefix), name=name, compartment=target_comp)
     model.add_metabolites([met])
+    met_index.setdefault((met.name, met.compartment), met)
     return met
 
 
@@ -202,6 +214,7 @@ def _stoichiometry(
     compartment: str | None,
     allow_new_mets: bool,
     new_met_prefix: str,
+    met_index: dict[tuple[str, str | None], Metabolite],
 ) -> tuple[dict[Metabolite, float], bool]:
     """Parse an equation into a {Metabolite: net coefficient} dict + reversibility."""
     lhs, rhs, reversible = _split_equation(equation)
@@ -217,7 +230,8 @@ def _stoichiometry(
             met = None
             if fallback is not None:
                 met = _try_existing(
-                    model, fallback, mets_by=mets_by, compartment=compartment
+                    model, fallback, mets_by=mets_by, compartment=compartment,
+                    met_index=met_index,
                 )
                 if met is not None:
                     coeff = 1.0
@@ -229,6 +243,7 @@ def _stoichiometry(
                     compartment=compartment,
                     allow_new_mets=allow_new_mets,
                     new_met_prefix=new_met_prefix,
+                    met_index=met_index,
                 )
             coeffs[met] = coeffs.get(met, 0.0) + sign * coeff
     # Drop metabolites that net to zero (present as both substrate and product).
@@ -295,6 +310,7 @@ def add_reactions_from_equations(
 
     known_genes = {gene.id for gene in model.genes}
     added: list[Reaction] = []
+    met_index = _build_met_index(model)
 
     for spec in reactions:
         if "id" not in spec:
@@ -316,6 +332,7 @@ def add_reactions_from_equations(
             compartment=compartment,
             allow_new_mets=allow_new_mets,
             new_met_prefix=new_met_prefix,
+            met_index=met_index,
         )
 
         rxn = Reaction(rxn_id, name=spec.get("name", ""))
diff --git a/src/raven_python/manipulation/change.py b/src/raven_python/manipulation/change.py
index 073fdfd..95808d2 100644
--- a/src/raven_python/manipulation/change.py
+++ b/src/raven_python/manipulation/change.py
@@ -18,7 +18,7 @@
 import cobra
 from cobra import Reaction
 
-from raven_python.manipulation.add import _stoichiometry
+from raven_python.manipulation.add import _build_met_index, _stoichiometry
 
 __all__ = ["change_reaction_equations", "change_gene_reaction_rules"]
 
@@ -60,6 +60,7 @@ def change_reaction_equations(
         raise ValueError(f"mets_by must be 'id' or 'name', got {mets_by!r}")
 
     changed: list[Reaction] = []
+    met_index = _build_met_index(model)
     for rxn_id, equation in equations.items():
         if rxn_id not in model.reactions:
             raise ValueError(f"Reaction {rxn_id!r} not found in the model.")
@@ -72,6 +73,7 @@ def change_reaction_equations(
             compartment=compartment,
             allow_new_mets=allow_new_mets,
             new_met_prefix=new_met_prefix,
+            met_index=met_index,
         )
 
         rxn.subtract_metabolites(dict(rxn.metabolites), combine=True)
diff --git a/src/raven_python/reconstruction/homology/homology.py b/src/raven_python/reconstruction/homology/homology.py
index bc6fa41..d5400a4 100644
--- a/src/raven_python/reconstruction/homology/homology.py
+++ b/src/raven_python/reconstruction/homology/homology.py
@@ -153,8 +153,14 @@ def _ortholog_map(
     if pairs.empty:
         return {}
 
-    # Keep only template genes that actually exist in their model.
-    pairs = pairs[pairs.apply(lambda r: r.template_gene in model_genes.get(r.model_id, ()), axis=1)]
+    # Keep only template genes that actually exist in their model. A list
+    # comprehension over the columns avoids DataFrame.apply(axis=1)'s per-row
+    # Series construction (model_genes values are sets, so membership is O(1)).
+    keep = [
+        tg in model_genes.get(mid, ())
+        for mid, tg in zip(pairs.model_id, pairs.template_gene, strict=True)
+    ]
+    pairs = pairs[keep]
 
     ortho: dict = {}
     for model_id, template_gene, new_gene in zip(pairs.model_id, pairs.template_gene, pairs.new_gene, strict=True):
diff --git a/tests/test_manipulation_add.py b/tests/test_manipulation_add.py
index 2a3a9d3..3ba2153 100644
--- a/tests/test_manipulation_add.py
+++ b/tests/test_manipulation_add.py
@@ -114,6 +114,25 @@ def test_name_mode_creates_new_met_with_auto_id(model):
     assert new[0].compartment == "c"
 
 
+def test_name_mode_dedups_new_met_across_reactions(model):
+    # A new metabolite named on more than one reaction in the same call must be
+    # created once and shared — later tokens have to see mets created earlier in
+    # the call (the (name, comp) index is seeded once and updated on creation).
+    r1, r2 = add_reactions_from_equations(
+        model,
+        [
+            {"id": "R1", "equation": "ATP --> AMP"},
+            {"id": "R2", "equation": "AMP --> ADP"},
+        ],
+        mets_by="name",
+        compartment="c",
+    )
+    amp = [m for m in model.metabolites if m.name == "AMP"]
+    assert len(amp) == 1                 # created once, not duplicated
+    assert amp[0] in r1.metabolites
+    assert amp[0] in r2.metabolites
+
+
 def test_name_mode_requires_compartment(model):
     with pytest.raises(ValueError, match="needs a compartment"):
         add_reactions_from_equations(