⚠ Few Patients, Each One FoundModerate threat

Amgen (AMGN) — threat to the moat

Horizon's ultra-rare drugs shrank 5% in 2025, a reminder that a disease with few patients runs out of new ones.

Rare-disease drugs have a simple economic problem: there are only so many patients. Horizon's ultra-rare products sold $758 million in 2024 and $719 million in 20251, a fall of about 5%2, in a year when Amgen's product sales rose 10%3.

Horizon product growth, 2025 (%)+72.8%UPLIZNA+13.1%KRYSTEXXA+2.8%TEPEZZA-5.1%Ultra-rareAmgen FY2025 results release; growth calculated
Two growing, one slowing, one shrinking.

A drug for a disease with a few thousand patients reaches a plateau once most diagnosed patients are treated. After that, growth depends on diagnosing new ones or on price, and price in rare disease is visible and politically sensitive. The ultra-rare decline suggests that some of these products have reached that plateau.

The same logic will eventually apply to the larger Horizon drugs. TEPEZZA's growth slowed to about 3% in 20254. A drug that treats a rare condition can grow quickly while the diagnosed pool is being treated for the first time and then slow sharply.

The risk for Amgen is that it paid a price for Horizon, $27.8 billion5, that assumed years of growth, and part of the portfolio is already showing the plateau. The second-quarter 2026 sales of the ultra-rare products, $149 million6, and of KRYSTEXXA and UPLIZNA are the counterweight.

The warning sign would be TEPEZZA following the ultra-rare products into decline. If TEPEZZA's 2026 sales come in below the $1,903 million of 20257, two of Horizon's four businesses will be shrinking within three years of the purchase, and the growth case for the price will rest on KRYSTEXXA and UPLIZNA alone.

References
  1. ReportedHorizon's ultra-rare products sold $758 million in 2024 and $719 million in 2025, a fall of about 5%, in a year when Amgen's product sales rose 10%.
    Amgen fourth-quarter and full-year 2025 results release, Form 8-K exhibit 99.1 - product sales for 2024-2025, non-GAAP EPS and 2026 guidance. — FY2025 · publ. 3 February 2026 · source ↗
  2. Moat Explorer calcHorizon's ultra-rare products sold $758 million in 2024 and $719 million in 2025, a fall of about 5%, in a year when Amgen's product sales rose 10%.
    Moat Explorer calculation from Amgen's reported product sales and financial statements ($ millions unless stated). Sales deductions: 2019 rebates 6,825 + chargebacks 7,090 + other 1,292 = 15,207; 2025 21,697 + 16,988 + 3,298 = 41,983; 41,983 / 35,148 = 1.19 times net product sales; implied gross product sales 35,148 + 41,983 = 77,131. Growth 2019-2025: deductions 41,983 / 15,207 = 2.76 times; net product sales 35,148 / 22,204 = 1.58 times (up 58%); rebates 21,697 / 6,825 = 3.18 times; chargebacks 16,988 / 7,090 = 2.4 times. Wholesalers 2025 gross: 26,253 + 20,986 + 12,562 = 59,801; 59,801 / 36,751 = 1.63 times total revenues; McKesson 26,253 / 36,751 = 71%. ENBREL: 2,226 / 5,433 - 1 = -59%; share of product sales 5,226 / 22,204 = 23.5% (2019), 2,226 / 35,148 = 6.3% (2025). ENBREL + Otezla 2025: 2,226 + 2,265 = 4,491; 4,491 / 36,751 = 12%. Otezla sales 2020-2025: 2,195 + 2,249 + 2,288 + 2,188 + 2,126 + 2,265 = 13,311; impairment 1,200 / 13,400 = 9%. Horizon products: 2023 448 + 272 + 65 + 164 = 949; 2024 1,851 + 1,185 + 379 + 758 = 4,173; 2025 1,903 + 1,340 + 655 + 719 = 4,617, 4,617 / 27,800 = 16.6%; Q2 2026 576 + 400 + 335 + 149 = 1,460, x4 = 5,840. TEPEZZA + KRYSTEXXA 2025 1,903 + 1,340 = 3,243; KRYSTEXXA 1,340 / 1,185 - 1 = 13.1%; TEPEZZA 1,903 / 1,851 - 1 = 2.8%; UPLIZNA 655 / 379 - 1 = 72.8%; H1 2026 262 + 335 = 597; ultra-rare 719 / 758 - 1 = -5.1%; UPLIZNA + ultra-rare 655 + 719 = 1,374. TAVNEOS H1 2026 119 + 150 = 269. Acquisitions: 13.4 + 3.9 + 27.8 = 45.1 bn; acquired products 2025 2,265 + 459 + 4,617 = 7,341, 7,341 / 36,751 = 20%. Interest 2,755 / 9,080 = 30%. Net debt 30 June 2026: 57.3 - 13.989 = 43.3 bn. Goodwill + intangibles 18,680 + 22,276 = 40,956, 40,956 / 90,586 = 45%. EPS gap 21.84 - 14.23 = 7.61. R&D 7,272 / 4,784 - 1 = 52%; 7,272 / 36,751 = 19.8%. Growth drivers 2025: Repatha 3,016 + EVENITY 2,100 + TEZSPIRE 1,478 + BLINCYTO 1,559 = 8,153 (2024: 2,222 + 1,563 + 972 + 1,216 = 5,973; 2023: 1,635 + 1,160 + 567 + 861 = 4,223; 2021: 1,117 + 530 + 0 + 472 = 2,119; 2019: 661 + 189 + 0 + 312 = 1,162); 8,153 / 5,973 - 1 = 36.5%, about 37%; 8,153 / 36,751 = 22%. Repatha 3,016 / 661 = 4.6 times, 3,016 / 2,222 - 1 = 36%; EVENITY 2,100 / 189 = 11 times; BLINCYTO 1,559 / 312 = 5.0 times. KYPROLIS 1,412 / 1,503 - 1 = -6%; KYPROLIS + Nplate 1,412 + 1,524 = 2,936, 2,936 / 6,660 = 44%; BLINCYTO + IMDELLTRA 1,559 + 627 = 2,186; Q2 2026 472 + 288 = 760. IMDELLTRA run rate 288 x 4 = 1,152, 1,152 / 6,498 = 18%. Biosimilars: 2025 AMJEVITA 597 + PAVBLU 700 + WEZLANA 273 + MVASI 771 + in other products 683 = 3,024; 3,024 / 35,148 = 8.6% of product sales; 3,024 / 36,751 = 8.2% of total revenues; PAVBLU 700 / 3,024 = 23%; AMJEVITA 597 / 761 - 1 = -22%; band 2022 1,831 / 2,177 - 1 = -16%; in other products 683 / 667 - 1 = 2%; WEZLANA and other biosimilars added (273 - 27) + (683 - 667) = 262; Q2 2026 155 + 287 + 61 + 153 + 199 = 855; Q2 2025 133 + 130 + 35 + 191 + 172 = 661; 855 / 661 - 1 = 29%; shares of total revenues 568 / 23,362 = 2.4% (2019), 2,177 / 25,979 = 8.4% (2021), 1,916 / 28,190 = 6.8% (2023). Bands 2025: general medicine and bone 3,016 + 2,100 + 4,414 + 2,084 = 11,614 (31.6%); inflammation and rare disease 2,226 + 2,265 + 1,478 + 1,903 + 1,340 + 655 + 459 + 719 = 11,045 (30.1%); oncology 1,559 + 627 + 1,175 + 1,412 + 363 + 1,524 = 6,660 (18.1%); biosimilars 3,024 (8.2%); established and other 1,389 + 435 + 353 + (1,311 - 683 = 628) + 1,603 = 4,408 (12.0%); total 36,751. 2019 bands 5,457; 5,404; 2,895; 568; 9,038; total 23,362. General medicine 11,614 / 5,457 = 2.1 times, 11,614 / 10,384 - 1 = 11.8%; inflammation 2020 7,191, 2024 10,870 / 7,535 - 1 = 44%, 2025 11,045 / 10,870 - 1 = 1.6%, non-ENBREL-Otezla 11,045 - 4,491 = 6,554; oncology 6,660 / 2,895 = 2.3 times, 6,660 / 5,685 - 1 = 17.2%; established 4,408 / 9,038 = 0.49. Q2 bands 2026 vs 2025: general medicine 953 + 714 + 759 + 352 = 2,778 vs 696 + 518 + 1,122 + 532 = 2,868, down 3%; Repatha + EVENITY 1,667 vs 1,214; denosumab 1,111 vs 1,654, down 33%; inflammation 3,167 vs 604 + 618 + 342 + 505 + 349 + 176 + 110 + 183 = 2,887, up 9.7%; oncology 1,953 vs 384 + 134 + 305 + 378 + 90 + 369 = 1,660, up 17.7%; established and other 632 + (351 - 199) + 517 = 1,301 vs 359 + 82 + 92 + (334 - 172) + 408 = 1,103, up 18%. Denosumab 2025 4,414 + 2,084 = 6,498, 6,498 / 36,751 = 17.7%; Q1 2026 727 + 411 = 1,138; H1 2026 1,486 + 763 = 2,249 vs 2,221 + 1,098 = 3,319. Neulasta 435 / 4,534 - 1 = -90%. Geography: US 25,656 / 35,148 = 73%; rest of world 9,492 / 35,148 = 27.0%; Q2 2026 2,547 / 9,537 = 26.7%; AMJEVITA 129 / 155 = 83.2%; Aranesp 258 / 352 = 73.3%; ENBREL 6 / 580 = 1.0%. Novartis-facing 2025 3,016 + 2,265 + 2,226 + 1,524 + 1,478 = 10,509, 10,509 / 36,751 = 29%. Other revenues 1,603 / 36,751 = 4.4%. Receivables 9,570 / 6,782 - 1 = 41%. Guidance midpoints: (37.0 + 38.4) / 2 = 37.7; (37.1 + 38.5) / 2 = 37.8; (38.2 + 39.4) / 2 = 38.8; non-GAAP EPS (22.30 + 23.50) / 2 = 22.90. IRS: 3.6 + 5.1 + 2.0 = 10.7 bn before interest; offsets 0.9 + 2.2 = 3.1 bn; 10.7 / 7.711 = 1.4 times 2025 net income; 10.7 / 224.15 = 4.8% of market value. Trailing free cash flow 8,100 - 2,891 + 4,966 = 10,175; 10,175 / 224,150 = 4.5%. Shares 538.8 / 629.6 - 1 = -14%. Gross margin (total revenues - cost of sales) / total revenues: (28,190 - 8,451) / 28,190 = 70.0% (2023); (33,424 - 12,858) / 33,424 = 61.5% (2024); (36,751 - 12,037) / 36,751 = 67.2% (2025). Pre-tax income 2025 7,711 + 1,265 = 8,976. Total revenues 36,751 / 21,662 = 1.70 times 2015. Market value 224.15 / 176.25 - 1 = 27% in 2026; added 224.15 - 176.25 = 47.9 bn against 176.25 - 122.45 = 53.8 bn in 2015-2025. Trailing net income 7,711 - 3,162 + 4,194 = 8,743; trailing revenue 36,751 - 17,328 + 18,672 = 38,095 - product and band totals, growth and sales deductions. — 2015-2026 · publ. September 2026 · source ↗
    Method: Arithmetic on figures reported in Amgen's Forms 10-K, 10-Q, results releases and market data; operands shown in the source line.
  3. ReportedHorizon's ultra-rare products sold $758 million in 2024 and $719 million in 2025, a fall of about 5%, in a year when Amgen's product sales rose 10%.
    Amgen Form 10-K for fiscal 2025 - Item 7 MD&A: product sales, sales deductions and customer concentration. — FY2025 · publ. 13 February 2026 · source ↗
  4. Moat Explorer calcTEPEZZA's growth slowed to about 3% in 2025.
    Moat Explorer calculation from Amgen's reported product sales and financial statements ($ millions unless stated). Sales deductions: 2019 rebates 6,825 + chargebacks 7,090 + other 1,292 = 15,207; 2025 21,697 + 16,988 + 3,298 = 41,983; 41,983 / 35,148 = 1.19 times net product sales; implied gross product sales 35,148 + 41,983 = 77,131. Growth 2019-2025: deductions 41,983 / 15,207 = 2.76 times; net product sales 35,148 / 22,204 = 1.58 times (up 58%); rebates 21,697 / 6,825 = 3.18 times; chargebacks 16,988 / 7,090 = 2.4 times. Wholesalers 2025 gross: 26,253 + 20,986 + 12,562 = 59,801; 59,801 / 36,751 = 1.63 times total revenues; McKesson 26,253 / 36,751 = 71%. ENBREL: 2,226 / 5,433 - 1 = -59%; share of product sales 5,226 / 22,204 = 23.5% (2019), 2,226 / 35,148 = 6.3% (2025). ENBREL + Otezla 2025: 2,226 + 2,265 = 4,491; 4,491 / 36,751 = 12%. Otezla sales 2020-2025: 2,195 + 2,249 + 2,288 + 2,188 + 2,126 + 2,265 = 13,311; impairment 1,200 / 13,400 = 9%. Horizon products: 2023 448 + 272 + 65 + 164 = 949; 2024 1,851 + 1,185 + 379 + 758 = 4,173; 2025 1,903 + 1,340 + 655 + 719 = 4,617, 4,617 / 27,800 = 16.6%; Q2 2026 576 + 400 + 335 + 149 = 1,460, x4 = 5,840. TEPEZZA + KRYSTEXXA 2025 1,903 + 1,340 = 3,243; KRYSTEXXA 1,340 / 1,185 - 1 = 13.1%; TEPEZZA 1,903 / 1,851 - 1 = 2.8%; UPLIZNA 655 / 379 - 1 = 72.8%; H1 2026 262 + 335 = 597; ultra-rare 719 / 758 - 1 = -5.1%; UPLIZNA + ultra-rare 655 + 719 = 1,374. TAVNEOS H1 2026 119 + 150 = 269. Acquisitions: 13.4 + 3.9 + 27.8 = 45.1 bn; acquired products 2025 2,265 + 459 + 4,617 = 7,341, 7,341 / 36,751 = 20%. Interest 2,755 / 9,080 = 30%. Net debt 30 June 2026: 57.3 - 13.989 = 43.3 bn. Goodwill + intangibles 18,680 + 22,276 = 40,956, 40,956 / 90,586 = 45%. EPS gap 21.84 - 14.23 = 7.61. R&D 7,272 / 4,784 - 1 = 52%; 7,272 / 36,751 = 19.8%. Growth drivers 2025: Repatha 3,016 + EVENITY 2,100 + TEZSPIRE 1,478 + BLINCYTO 1,559 = 8,153 (2024: 2,222 + 1,563 + 972 + 1,216 = 5,973; 2023: 1,635 + 1,160 + 567 + 861 = 4,223; 2021: 1,117 + 530 + 0 + 472 = 2,119; 2019: 661 + 189 + 0 + 312 = 1,162); 8,153 / 5,973 - 1 = 36.5%, about 37%; 8,153 / 36,751 = 22%. Repatha 3,016 / 661 = 4.6 times, 3,016 / 2,222 - 1 = 36%; EVENITY 2,100 / 189 = 11 times; BLINCYTO 1,559 / 312 = 5.0 times. KYPROLIS 1,412 / 1,503 - 1 = -6%; KYPROLIS + Nplate 1,412 + 1,524 = 2,936, 2,936 / 6,660 = 44%; BLINCYTO + IMDELLTRA 1,559 + 627 = 2,186; Q2 2026 472 + 288 = 760. IMDELLTRA run rate 288 x 4 = 1,152, 1,152 / 6,498 = 18%. Biosimilars: 2025 AMJEVITA 597 + PAVBLU 700 + WEZLANA 273 + MVASI 771 + in other products 683 = 3,024; 3,024 / 35,148 = 8.6% of product sales; 3,024 / 36,751 = 8.2% of total revenues; PAVBLU 700 / 3,024 = 23%; AMJEVITA 597 / 761 - 1 = -22%; band 2022 1,831 / 2,177 - 1 = -16%; in other products 683 / 667 - 1 = 2%; WEZLANA and other biosimilars added (273 - 27) + (683 - 667) = 262; Q2 2026 155 + 287 + 61 + 153 + 199 = 855; Q2 2025 133 + 130 + 35 + 191 + 172 = 661; 855 / 661 - 1 = 29%; shares of total revenues 568 / 23,362 = 2.4% (2019), 2,177 / 25,979 = 8.4% (2021), 1,916 / 28,190 = 6.8% (2023). Bands 2025: general medicine and bone 3,016 + 2,100 + 4,414 + 2,084 = 11,614 (31.6%); inflammation and rare disease 2,226 + 2,265 + 1,478 + 1,903 + 1,340 + 655 + 459 + 719 = 11,045 (30.1%); oncology 1,559 + 627 + 1,175 + 1,412 + 363 + 1,524 = 6,660 (18.1%); biosimilars 3,024 (8.2%); established and other 1,389 + 435 + 353 + (1,311 - 683 = 628) + 1,603 = 4,408 (12.0%); total 36,751. 2019 bands 5,457; 5,404; 2,895; 568; 9,038; total 23,362. General medicine 11,614 / 5,457 = 2.1 times, 11,614 / 10,384 - 1 = 11.8%; inflammation 2020 7,191, 2024 10,870 / 7,535 - 1 = 44%, 2025 11,045 / 10,870 - 1 = 1.6%, non-ENBREL-Otezla 11,045 - 4,491 = 6,554; oncology 6,660 / 2,895 = 2.3 times, 6,660 / 5,685 - 1 = 17.2%; established 4,408 / 9,038 = 0.49. Q2 bands 2026 vs 2025: general medicine 953 + 714 + 759 + 352 = 2,778 vs 696 + 518 + 1,122 + 532 = 2,868, down 3%; Repatha + EVENITY 1,667 vs 1,214; denosumab 1,111 vs 1,654, down 33%; inflammation 3,167 vs 604 + 618 + 342 + 505 + 349 + 176 + 110 + 183 = 2,887, up 9.7%; oncology 1,953 vs 384 + 134 + 305 + 378 + 90 + 369 = 1,660, up 17.7%; established and other 632 + (351 - 199) + 517 = 1,301 vs 359 + 82 + 92 + (334 - 172) + 408 = 1,103, up 18%. Denosumab 2025 4,414 + 2,084 = 6,498, 6,498 / 36,751 = 17.7%; Q1 2026 727 + 411 = 1,138; H1 2026 1,486 + 763 = 2,249 vs 2,221 + 1,098 = 3,319. Neulasta 435 / 4,534 - 1 = -90%. Geography: US 25,656 / 35,148 = 73%; rest of world 9,492 / 35,148 = 27.0%; Q2 2026 2,547 / 9,537 = 26.7%; AMJEVITA 129 / 155 = 83.2%; Aranesp 258 / 352 = 73.3%; ENBREL 6 / 580 = 1.0%. Novartis-facing 2025 3,016 + 2,265 + 2,226 + 1,524 + 1,478 = 10,509, 10,509 / 36,751 = 29%. Other revenues 1,603 / 36,751 = 4.4%. Receivables 9,570 / 6,782 - 1 = 41%. Guidance midpoints: (37.0 + 38.4) / 2 = 37.7; (37.1 + 38.5) / 2 = 37.8; (38.2 + 39.4) / 2 = 38.8; non-GAAP EPS (22.30 + 23.50) / 2 = 22.90. IRS: 3.6 + 5.1 + 2.0 = 10.7 bn before interest; offsets 0.9 + 2.2 = 3.1 bn; 10.7 / 7.711 = 1.4 times 2025 net income; 10.7 / 224.15 = 4.8% of market value. Trailing free cash flow 8,100 - 2,891 + 4,966 = 10,175; 10,175 / 224,150 = 4.5%. Shares 538.8 / 629.6 - 1 = -14%. Gross margin (total revenues - cost of sales) / total revenues: (28,190 - 8,451) / 28,190 = 70.0% (2023); (33,424 - 12,858) / 33,424 = 61.5% (2024); (36,751 - 12,037) / 36,751 = 67.2% (2025). Pre-tax income 2025 7,711 + 1,265 = 8,976. Total revenues 36,751 / 21,662 = 1.70 times 2015. Market value 224.15 / 176.25 - 1 = 27% in 2026; added 224.15 - 176.25 = 47.9 bn against 176.25 - 122.45 = 53.8 bn in 2015-2025. Trailing net income 7,711 - 3,162 + 4,194 = 8,743; trailing revenue 36,751 - 17,328 + 18,672 = 38,095 - product and band totals, growth and sales deductions. — 2015-2026 · publ. September 2026 · source ↗
    Method: Arithmetic on figures reported in Amgen's Forms 10-K, 10-Q, results releases and market data; operands shown in the source line.
  5. ReportedThe risk for Amgen is that it paid a price for Horizon, $27.8 billion, that assumed years of growth, and part of the portfolio is already showing the plateau.
    Amgen Form 10-K for fiscal 2023 - the Horizon and ChemoCentryx acquisitions, their purchase-price allocation and the debt that funded them; sales deductions for 2021-2023. — FY2023 · publ. February 2024 · source ↗
  6. ReportedThe second-quarter 2026 sales of the ultra-rare products, $149 million, and of KRYSTEXXA and UPLIZNA are the counterweight.
    Amgen second-quarter 2026 results release, Form 8-K exhibit 99.1 - product sales performance: inflammation, rare disease and established products, and sales by region. — Q2 2026 · publ. 4 August 2026 · source ↗
  7. ReportedIf TEPEZZA's 2026 sales come in below the $1,903 million of 2025, two of Horizon's four businesses will be shrinking within three years of the purchase, and the growth case for the price will rest on KRYSTEXXA and UPLIZNA alone.
    Amgen fourth-quarter and full-year 2025 results release, Form 8-K exhibit 99.1 - product sales for 2024-2025, non-GAAP EPS and 2026 guidance. — FY2025 · publ. 3 February 2026 · source ↗
Sources
Generated September 28, 2026