Merck's Keytruda Dependency: A Growth Story With An Expiration Date

Merck's reliance on Keytruda, which accounts for 46% of total revenue and whose sales jumped 72% from 2021 to 2023, presents a significant risk as its U.S. market exclusivity ends in 2028, opening the door for biosimilar competition and potentially causing a sharp decline in sales from a projected peak of $36 billion to below $15 billion within 4-5 years; this looming patent cliff, coupled with falling demand for Gardasil, creates a critical three-year window for Merck to diversify its revenue streams or face slower growth and a potential valuation decline, as reflected in the stock's 40% drop over the past year.

Analysis

Merck faces a substantial impending challenge due to its significant reliance on the oncology drug Keytruda, which constituted 46% of the company's total revenue and saw sales surge by 72% from $17 billion in 2021 to $29 billion in 2023, driving Merck's average double-digit revenue growth over the past three years. This success is overshadowed by Keytruda's U.S. market exclusivity ending in 2028, which will introduce biosimilar competition, a development with high certainty. Projections suggest Keytruda's sales, after potentially peaking near $36 billion by 2028, could plummet to $20 billion or even below $15 billion within four to five years post-exclusivity. This mirrors the severe revenue erosion experienced by other blockbuster drugs facing biosimilars, such as AbbVie’s Humira, which lost approximately 60% of its revenue, and Roche’s Herceptin. Further pressuring Merck is the declining demand for its second-largest drug, Gardasil, particularly in China. Consequently, Merck's growth is expected to decelerate significantly post-2028, a risk that may already be partially priced into the stock, which has fallen 40% over the past year, presenting a critical three-year window for the company to secure new revenue streams.

Key Decisions for Investors

• Investors should closely monitor Merck's strategic initiatives over the next three years, particularly its R&D pipeline progress and any M&A or licensing deals aimed at mitigating the anticipated revenue loss from Keytruda's patent expiration in 2028.
• Given Keytruda's 46% contribution to total revenue and the severe impact biosimilars have historically had on drugs like Humira, the risk of significant valuation pressure on MRK persists as the 2028 patent cliff approaches, even after its recent 40% stock decline.
• Consider the compounding risk from falling Gardasil demand, especially in China, when assessing Merck's ability to offset the Keytruda revenue gap and maintain growth beyond 2028.
• The Merck situation highlights the critical need for portfolio diversification; investors with significant holdings in MRK should evaluate their exposure to single-product concentration risk within the pharmaceutical sector.