(Reuters) - Cigna plans to make close copies of AbbVie's blockbuster arthritis drug Humira available with no out-of-pocket payment to eligible patients in the U.S. using its specialty pharmacy beginning in June, the health insurer said on Thursday.

Cigna said it will stock high- and low-concentration biosimilar versions of Humira from drugmakers including Boehringer Ingelheim, Teva and Alvotech at its Accredo pharmacy.

"Not all biosimilars are created equal," Matt Perlberg, president of Cigna's Evernorth Health Services' pharmacy and care delivery businesses, said in an interview. "We know that patients need options, and we wanted to make sure that we offer the right experience, level of clinical care, and affordability for as many eligible patients as possible."

Unlike easy to manufacture pills that can be copied and sold as generics at a huge discount once patents lapse, complex biologic medicines made from living cells cannot be exactly duplicated. Their close alternatives are called biosimilars.

Despite nine biosimilars being launched in the U.S. last year, AbbVie has held onto more than 98% of the Humira market. Privately-held German drugmaker Boehringer launched its version, Cyltezo, last July but has only managed to sell a couple thousand prescriptions in total since then, according to IQVIA data.

Almost 3 million Humira prescriptions have been written during the same period, although tens of thousands of scripts have started to shift to biosimilar Hyrimoz each week since CVS Health's pharmacy benefits unit took Humira off the list of drugs it recommends insurers reimburse. Hyrimoz is made by Switzerland's Sandoz.

Cyltezo and Simlandi, from Israel's Teva and Iceland's Alvotech, are designated as interchangeable, meaning they can be substituted for the original without consulting the prescriber.

Simlandi, which was approved in the U.S. in February, is the only interchangeable biosimilar of Humira that also comes in a high-concentration dose.

AbbVie's high-concentration version of Humira makes up close to 90% of its sales in the United States.

Cigna said these biosimilars will be priced at about 85% lower than the $6,922.62 monthly list price of Humira, and that it had made agreements with the manufacturers as well as its distributor Quallent to bring the out-of-pocket cost down to $0.

The company said the move should save around $3,500 on average per year for some of the 100,000 Accredo patients currently using either Humira or one of its biosimilars. Perlberg did not provide an estimate for how many patients they anticipate switching.

"Different patients adopt products at different times," said Perlberg.