CVS Health Corp., which operates the nation’s second-biggest pharmacy benefit manager, said that next year it will exclude an additional 31 prescription medicines from insurance coverage, including Viagra and widely used treatments for diabetes and multiple sclerosis.

The 2016 excluded drugs, disclosed on Wednesday, also include Vivus Inc.’s weight loss treatment Qsymia, which last week was excluded from the 2016 formulary of CVS rival Express Scripts Holding Co. Vivus officials could not immediately be reached for comment.

Pharmacy benefit managers, or PBMs, which administer drug benefits for employers and health plans and also run large mail-order pharmacies, have been challenging the rising cost of new medications. When drugs are knocked off their formularies, patients may have to pay full price for them. PBMs often keep or dump a product depending on whether they can obtain favorable pricing.

Viagra, the world’s first approved pill for erectile dysfunction, has annual sales of $1.8 billion, including $1.3 billion in the United States. Cheaper generic versions are expected to be launched by December 2017.

“Pfizer is committed to ensuring patient access to our medicines,” the drugmaker said in an emailed statement.

The CVS formulary, however, does include Eli Lilly and Co.’s rival Cialis anti-impotence treatment.

Next year’s formulary will also exclude two interferon-based multiple sclerosis treatments from Biogen, big-selling Avonex and its new longer-acting Plegridy. Avonex, Biogen’s second-biggest product, has annual sales of almost $2.5 billion.

“Avonex and Plegridy have broad insurance coverage,” Biogen said in an emailed statement. “We are confident that patients will continue to have access to our medicines.”

Johnson & Johnson’s two-year-old diabetes treatment, Invokana, and a related combination treatment called Invokamet, will also be stripped from CVS coverage. Combined sales of the medicines have been growing by leaps and bounds, reaching $318 million in the second quarter. J&J did not have an immediate comment.

Another diabetes drug to be excluded from the CVS formulary is Bydureon, a once-weekly treatment from AstraZeneca Plc. CVS will favor instead similar treatments from Lilly and Novo Nordisk.

“Bydureon continues to have excellent access across commercial and non-commercial plans, including (Medicare) Part D,” AstraZeneca said.

Express Scripts, the nation’s biggest PBM, last week said it would boot about 20 additional medicines from its formulary in 2016.

Express Scripts said it can negotiate lower drug prices through its ability to exclude drugs from its coverage list. The formulary determines whether tens of millions of people with private insurance can easily use an insurance co-pay to buy prescription drugs.