Rising specialty drug use is outpacing what PBM rebate guarantees save self-funded employers

A rebate guarantee works on the price of each prescription. The cost growth in the survey data comes from the number of people filling one. The illustration in the hcamag.com account uses round numbers: 100 members on a $10,000-a-year therapy cost $1 million, and a negotiated 10 percent price cut saves $100,000 ^[5]. If the patient count reaches 140 over the same period, spend rises to $1.26 million, up 26 percent despite the lower price ^[6]. On those terms the discount is used up once the patient count passes about 111, or roughly 11 percent growth ^[22].

That example is hypothetical. The population data point the same way. Pharmaceutical Strategies Group found the share of members using at least one specialty drug rose from 4.4 percent in 2023 to 5.5 percent ^[13], a relative increase of 25 percent ^[23]. One plan's experience will differ from a national average, and the PSG change covers more than one plan year. Even so, 25 percent growth in users is about 2.25 times the growth that would cancel a 10 percent price cut ^[24].

Paul Pruitt is chief growth officer and co-founder of SHARx, a procurement platform for high-cost prescription drugs ^[8]. "CFOs should focus on the total pharmacy spend, not the savings percentage printed in the contract," he said ^[7]. His company sells drug procurement, so he has a commercial stake in how employers judge their PBMs. The utilization figures above do not depend on him.

The guarantee has a real defense. It is a contractual number a finance team can enforce, while utilization depends on diagnoses and prescribing the employer does not control. The American Journal of Managed Care research weakens that defense. Its authors warned that guarantee arrangements may obscure an employer's view of net drug prices, potentially steering formularies toward higher-cost products and lifting total pharmacy costs ^[10].

The obvious response to a rising specialty line is to restrict coverage. Pruitt argues blunt restrictions shift costs without resolving them, leading to employee complaints, absenteeism and eroded trust in the benefit ^[19]. He favors clinical guidelines, utilization management, patient advocacy and adherence support ^[20]. The trade-off is a smaller pharmacy line this year against costs that, on his account, turn up elsewhere. His renewal starting point is the budget, split into separate lines for GLP-1s, specialty medications, oncology, autoimmune treatments and high-cost infusions, with every line watched for new-to-therapy and continuation rates and for pipeline therapies close to becoming eligible for coverage ^[21].

The calendar separates two decisions. Business Group on Health found 47 percent of employers weighing a move for 2028 or 2029 to transparent or new-generation PBM models ^[18]. Those models pass rebates directly to plan sponsors and disclose net drug costs ^[18]. More than half of employers still with the big three are considering a switch ^[17]. The survey figures do not show whether employers that already left saw total spend fall, so on this record the case for switching rests on visibility into net cost. I think the 2027 renewal matters most for what it records. A plan that renews on guarantee size reaches 2028 with rebate percentages to compare. A plan that renews with utilization reporting by therapy class reaches it with a spend baseline.