Peter Griffith
Executive Vice President and Chief Financial Officer at Amgen
Thank you, Jay. We're pleased with our strong execution and performance in the fourth quarter and for the full year 2023. In the fourth quarter, total revenue of $8.2 billion grew 20% year-over-year and non-GAAP EPS of $4.71 grew 15% year-over-year.
For the full year, we delivered total revenue of $28.2 billion, 7% growth year-over-year and non-GAAP EPS of $18.65, 5% growth year-over-year. As a reminder, both Q4 and the full year results include Horizon's results beginning October 6, when the acquisition closed, so our financial results will exclude approximately one week of Horizon's results from our fourth quarter results. I'll review the details of our fourth quarter and full year financial results before discussing our outlook for 2024. The financial results are shown on Slides 54 to 56 of the slide deck.
Turning to our fourth quarter total revenue of $8.2 billion. We saw product sales increased 20% year-over-year, driven by volume growth of 23%, offset by net selling price decline of 3%. Excluding the impact of Horizon, product sales increased 5% year-over-year driven by volume growth of 9%. Full year total revenues of $28.2 billion grew 7% year-over-year. Product sales increased 9% year-over-year, driven by 15% volume growth.
Other revenues decreased 16% year-over-year, primarily due to lower profit and cost sharing from our COVID-19 collaboration with Lilly in 2022. Strong expense discipline resulted in a 50% non-GAAP operating margin as a percentage of product sales for the full year 2023. While we continue to focus on both internal and extension, investing $4.7 billion in our pipeline and $27.8 billion in our acquisition of Horizon.
With product sales volume growth at 23% in Q4 and 15% for the full year, we still efficiently manage the operating expenses of the business. Q4 non-GAAP operating expenses increasing 18% year-over-year, while full year non-GAAP operating expenses increased 9%. Excluding the impact of Horizon, Q4 non-GAAP operating expenses increased 3% and full year non-GAAP operating expenses increased 5%.
On a non-GAAP basis, Q4 cost of sales as a percentage of product sales was flat on a year-over-year basis at 16.3%. For the full year, cost of sales as a percentage of product sales increased by 1.1 percentage points to 17.0%. The full year increase was primarily driven by higher profit share and changes in our product mix, partially offset by the replacement of the Puerto Rico excise tax with an income tax beginning in 2023.
Non-GAAP R&D spend in the fourth quarter increased 16% year-over-year and 8% year-over-year for the full year primarily due to higher spend on later-stage clinical programs and marketed product support, including spend on programs acquired from the Horizon acquisition and continuing investment in our pipeline, including MariTide.
Q4 non-GAAP SG&A expenses increased 20% year-over-year, primarily driven by commercial and G&A expenses related to the Horizon acquisition. Full year non-GAAP SG&A expenses increased 5% year-over-year, primarily driven by commercial and G&A expenses related to the Horizon acquisition, partially offset by a decline in other marketed product spend.
Non-GAAP OI&E were about $635 million in expense in the fourth quarter, a $168 million increase year-over-year, primarily driven by increased interest expense related to the debt issued for the Horizon acquisition. Full year non-GAAP OI&E was favorable $279 million year-over-year, primarily driven by the change in accounting for the BeiGene investment to the fair value mark-to-market method and by gains related to early debt retirement, partially offset by higher net interest expense.
Our non-GAAP tax rate increased 2.5 percentage points year-over-year to 15.9% in the fourth quarter and 2.7 percentage points year-over-year to 16.5% for the full year, primarily due to the 2022 Puerto Rico tax law change mentioned previously. The company generated $7.4 billion of free cash flow in 2023 compared with $8.8 billion in 2022. The decrease is driven by the Horizon transaction and integration costs higher repatriation tax payments and higher capital expenditures. We expect to continue to generate strong cash flows with the addition of Horizon and are on track with our deleveraging plans to return to our efficient capital structure by the end of 2025.
In summary, we continue to execute on our multiple capital allocation priorities. First, we continue to prioritize investments in both internal and external innovation. Our increased spending and non-GAAP R&D of 8% in '23 over '22, coupled with the acquisition of Horizon Therapeutics continues to broaden and strengthen our balanced portfolio across therapeutic areas. With our strong late-stage innovative pipeline moving forward through development, we expect our non-GAAP R&D to continue to increase in 2024.
Second, we continue investing in our business for long-term growth, including our state-of-the-art manufacturing facilities in Ohio and North Carolina. Amgen, Ohio, our new advanced assembly and final product packaging plant has just received license from the FDA for commercial production in January, roughly two years after we broke ground, and our innovative drug acceptance plan under construction in North Carolina is expected in the operational by 2026.
In addition, we've positioned the organization to accelerate investments in innovation, including leveraging the power of generative artificial intelligence. And third, we return capital to shareholders through growing dividends including $2.13 per share in the quarter. This represented a 10% increase over that paid in each of 2022's four quarters.
Turning to the outlook for the business for 2024. First, because this is the first full year incorporating the impact of Horizon, we're providing some additional granularity in our guidance, which we don't expect to be the same extent in the future. For 2024, we're expecting revenue of $32.4 billion to $33.8 billion and non-GAAP earnings per share of $18.90 to $20.30.
As we continue to integrate Horizon, we expect the acquisition to be accretive to non-GAAP EPS in 2024. We and we're on track to meet the synergy target previously communicated of at least $500 million in pre-tax cost by year three after closing or in 2026. Our revenue range reflects our strong growth outlook driven by numerous opportunities across our four therapeutic area pillars. We will record a full year of legacy Horizon product sales, and we expect continued volume-driven growth in our priority products, Repatha, TEZSPIRE, EVENITY, Otezla, Prolia and BLINCYTO, consistent with industry trends in our recent history, we expect mid single-digit price decline for our portfolio in 2024.
As a reminder, as you model the first quarter of 2024 and consistent with our historical trends, we expect first quarter product sales to be the lowest quarter as a percentage of the full year due to benefit plan changes, insurance reverifications and increased co-pay charges. So we expect the first quarter of 2024 total revenue to grow roughly 20% year-over-year. For the full year, we expect other revenue to be in the range of approximately $1.3 billion to $1.4 billion. And we continue to efficiently run the business through our disciplined approach to managing operating expenses.
In 2024, we're making incremental R&D investments to support our promising late-stage plan, including our rapidly advancing oncology programs as discussed following ESMO in October and other programs, including MariTide. Furthermore, the addition of Horizon has an impact on the 2024 operating margin given the timing of when synergies are realized. As a result, we project the full year non-GAAP operating margin as a percentage of product sales to be roughly 48%.
Note that we expect non-GAAP operating margin growth to accelerate in each of the quarters following the first quarter, there are primarily three reasons for this. First, typical lower product sales in Q1, as I mentioned above, and in each of the following quarters. Second, increased spend on our commercial brands will continue building on the investments we made in the second half of 2023, including Repatha, Otezla and our bone portfolio of EVENITY and Prolia.
And third, Q1 2024 reflects the addition of Horizon, for which we are just at the beginning stages of realizing synergies given the acquisition close date of October 6. So we expect non-GAAP operating margin to be roughly 43% in the first quarter.
I would reiterate that we expect operating margin growth to accelerate in each of the quarters following the first quarter. We project non-GAAP cost of sales to be in the range of 17% to 18% as a percentage of product sales for the 2024 year. Taking into account the full year of Horizon related expenses, we expect non-GAAP R&D expenses in 2024 to increase approximately 20% year-over-year. with investments also increasing to advance key pipeline assets, including AMG 193, MariTide, rocatinlimab and tarlatamab. We see significant potential in our innovative pipeline, and it is important that we strategically invest now to fully unlock the opportunities ahead, create long-term value for patients, staff, and shareholders.
And for non-GAAP SG&A spend, we expect 2024 full-year amounts as a percentage of product sales to be between 21% and 22%. We anticipate non-GAAP OI&E to be in the range of $2.6 billion to $2.7 billion. As mentioned on our Q3 '23 call, the '24 guidance includes the interest expense related to the $28 billion of debt rates for the Horizon acquisition.
We expect a non-GAAP tax rate of 16% to 17%. Our guidance is primarily being driven by two factors. The first is the jurisdictional mix of income, including the full-year benefits associated with the Horizon transaction. And the legal entity rationalization undertaken in the fourth quarter of 2023 in part to integrate the Horizon entities into our existing U.S. headquartered legal entity [Technical Issues] environment, although the deposit negatively affects our cash flow in '24. If any of the deposit is returned to us upon the resolution of our litigation, those funds would accrue interest income. Therefore, the radar bitrage makes this payment a prudent use of our capital. Once again, out of an abundance of clarity, this represents no change in our belief in the merits of the tax court case. The guidance also includes the impact of the adoption of the OECD, 15% minimum tax by certain jurisdictions. Based on our individual footprint, we don't anticipate any significant effects of the new rules in 2024, but we're closely watching the global tax landscape for future impacts as the framework continues to be considered by additional jurisdictions and new rules take effect. We expect governments around the world, including the United States to continue to look for more sources of tax revenue from large multinational corporations that could result in higher taxes in the coming years.
Similar to 2023, we expect share repurchases now to exceed $500 million in 2024. We expect that we will continue to increase our dividend. We expect capital expenditures of approximately $1.1 billion in 2024, consistent with our capital allocation priority to invest in our business, including the Ohio and North Carolina facilities I mentioned ahead and into the rare disease pillar.
In summary, we delivered another strong year of financial results in 2023. Our confidence in the long-term growth of Amgen is strong, and we believe that our new rare disease pillar, one of our four pillars will be an important additive source of growth for the company. This concludes the financial update. My thanks to my approximately 27,000 plus colleagues at Amgen around the world for their commitment to our mission of serving patients and their tireless efforts in 2023.
I'll turn it back to Bob for Q&A.