If you’re one of the 43 million diabetic or cancer patients in the US with a laundry list of prescribed medications, you could be in for a rude awakening next time you go to the pharmacy for a refill. The drugs you expect to take could have been “delisted,” according to The Doctor-Patient Rights Project (DPRP).

A study the group released last week shows that the number of prescribed remedies now excluded by two of the largest pharmacy benefit managers (PBMs) — Express Scripts (ESRX) and CVS Health (CVS) — has nearly tripled from four years ago. And the number of diabetes treatments both companies’ “formularies,” (the list of covered drugs) no longer include has jumped by nearly 80 percent, said the group.

The companies responded by saying they carefully evaluate medications before removing them from their lists to determine which are most — or least — effective. CVS referred a call for comment to the Pharmaceutical Care Management Association (PCMA), which represents the PBM industry. PCMA spokesperson Greg Lopes said in a statement that as a result of those evaluations, “we typically reduce drug costs by 30 percent.”

The DPRP, which includes doctors, patients and giant drug company Amgen (AMGN), didn’t dispute the right of these PBMs to eliminate the older or too-expensive drugs from the list of medications they dispense. “Exclusion lists can undoubtedly serve as important tools to help manage the skyrocketing cost of patient care,” said Stacey Worthy, speaking for the DPRP. “But these lists can cause stable patients to lose access to their medications in the middle of treatment. They must be implemented carefully so as not to disrupt care.”

The DPRP said studies have “called into question” the effectiveness of some of the substitute cancer drugs that get dispensed in place of the ones patients were already using. “Even substitution with a generic equivalent entails serious risk of reduced treatment effectiveness,” said the DPRP study. For diabetic drugs in particular, which have the most exclusions of any category, many low-income people simply “skip doses” of the original, more expensive drug rather than use the cheaper but ineffective substitute.

But some patients who skip or cut treatment of their original drug because the substitute doesn’t work ultimately end up in emergency rooms or hospitals and require even more care as their illnesses worsen, according to the DPRP. These cost-cutting measures by PBMs wind up costing patients — and in turn the nation’s health care system — more money.

A previous study by this doctors’ rights group, which only began this year, looked at the health insurers that hire these PBMs to negotiate discounts with the pharmaceutical companies. Express Scripts and CVS, which is planning to mergewith health insurer Aetna (AET), account for more than half the entire US PBM market, the DPRP noted.

In a separate statement, Express Scripts said “appropriateness of the drug — not the cost — is our foremost consideration.” It added that independent physicians make prescribing decisions that use “clinically superior medications while eliminating ‘me too options’ that have no added clinical benefit.”