(Reuters) – The U.S. Food and Drug Administration (FDA) has approved Novartis AG’s copy of Humira, the world’s bestselling prescription medicine developed by U.S.-based AbbVie Inc, the agency’s website showed on Wednesday.

Although approved, Novartis’ Sandoz unit can only begin U.S. sales of Humira’s biosimilar in 2023, according to a licensing agreement sealed with AbbVie this month.

The biosimilar, Hyrimoz, is approved for treating several diseases, including rheumatoid arthritis, the FDA said.

Biosimilar drugs are not exact replicas of medicines such as Humira, which are made in living cells, but they are similar enough to do the job.

Humira already faces competition from biosimilars in Europe.

AbbVie has signed a string of agreements with rival drugmakers including Mylan and Amgen, allowing it to maintain near-term control over when their copies will hit the U.S. market.

Humira raked in sales of $18.43 billion for AbbVie in 2017.

(Reporting by Manas Mishra in Bengaluru; Editing by Sai Sachin Ravikumar)