Shares of AstraZeneca PLC (AZN.US), the UK's largest pharmaceutical manufacturer, will begin trading on the New York Stock Exchange on Monday. This move follows the company's listing upgrade, which replaces its previously traded American Depositary Receipts (ADRs) on the Nasdaq. AstraZeneca will now be concurrently listed and traded on three exchanges: the London Stock Exchange, Nasdaq Stockholm, and the New York Stock Exchange. The vaccine and drug maker is seeking to attract more investors by further tilting towards the US market, which currently accounts for nearly half of its revenue. The company stated that this action will give its listing status in the UK, Sweden, and the US equal weight. This reflects the growing importance of the US market to AstraZeneca's business and signals a relative shift in focus away from its home country as CEO Pascal Soriot pursues growth in the world's largest pharmaceutical market. Subsequently, US investors will find it easier to purchase full shares of AstraZeneca, increasing the possibility that the relevance of its London listing could diminish. Amid pressure from former President Trump's tariff plans, AstraZeneca has committed to investing $50 billion in the United States by 2030. Concurrently, the company has paused a £200 million (approximately $274 million) expansion plan for its UK headquarters. Charles Hall, Head of Research at Peel Hunt, believes the long-term risk is that stock trading will predominantly shift to the US. In an October report, he stated, "Assuming liquidity increases significantly in the US, and given that most shares are held by international investors, we believe it is highly probable that over time the company will consider moving its primary listing from London to the US." This move will also allow investors to buy AstraZeneca shares without paying stamp duty, a UK transaction tax. Peel Hunt's report notes that this could lead to an annual loss of £200 million for the UK Treasury. If successful, this action might encourage other London-listed companies to replace their ADRs with ordinary shares, thereby further reducing stamp duty tax revenues. In recent years, trading volume for American Depositary Receipts (ADRs) of UK companies has surged. Data shows that between 2019 and 2024, trading volume for the 20 FTSE 100 companies with listed ADRs grew by over 80%. AstraZeneca's ADR trading volume increased by 34% in the five years to 2024, while trading volume on the London market grew by less than 8% over the same period. Several other prominent UK companies have also seen massive growth in ADR trading volume: Barclays Bank more than tripled, while Diageo Plc, British American Tobacco Plc, and GSK more than doubled. The UK has long struggled to compete with the US market, which is larger, more liquid, and home to numerous high-growth companies, whereas the UK market is dominated by traditional economic sectors with lower valuations. Although the UK stock market is at historic highs, its performance still lags behind that of the US. This divergence has been particularly pronounced since the COVID-19 pandemic: since the beginning of 2020, the FTSE 100 index has risen approximately 40% in US dollar terms, far short of the S&P 500's 115% gain.