I use Optum RX thru United Healthcare Preferred Part D drug coverage plan. My 90 day prescription went from $5 co-pay to $93.49 co-pay. When I inquired at United Healthcare they said the formulary was reclassified from a Tier 1 to Tier 3 how can they do that and why I use Optum RX thru United Healthcare Preferred Part D drug coverage plan. My 90 day prescription went from $5 co-pay to $93.49 co-pay. When I inquired at United Healthcare they said the formulary was reclassified from a Tier 1 to Tier 3 how can they do that and why?