When the model refuses

The most important thing about a model is knowing what it does not know. Lab refuses where the evidence is too thin or the harm is too real.

Hard refusals

• MAOI + serotonergic (SSRI, MDMA, tramadol) — serotonin syndrome risk
• Methylene blue + serotonergics — same mechanism
• Pregnancy + most pharmacology — model insufficient
• Under-18 + most pharmacology — out of scope

Soft refusals

• Stacking three or more low-confidence compounds
• Doses far outside literature range
• Combinations Lab has never modeled

What refusal looks like

• Warning banner on the timeline item
• AI declines to add the combination
• PK/PD sections in the inspector mark the affected signals as Unmodeled
• The combination fires a critical interaction (red border + chip on the timeline items)