ALNY vs SLN: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of August 2026). Valuation lined up like this is most meaningful for two names in the same corner of the market, which these are. Figures are approximate; verify before investing.

The metrics above tell you which is the marginally better business. The bigger risk for most people is not picking the slightly worse stock, it is over-concentrating. ALNY and SLN share themes, so owning both, or adding either to what you already hold, can quietly push a large share of your portfolio into one bet.

This is the part a generic comparison page cannot answer, because it depends on what you own. Connect your brokerage and Walnut shows your real, combined ALNY and SLN exposure, flags overlap with your existing positions, and tells you if adding one would tip you past a concentration you are comfortable with, read-only by default, with your login staying at your broker. Walnut is not an investment adviser.

Alnylam Pharmaceuticals is the company that turned RNA interference, a Nobel-winning biological mechanism for silencing disease-causing genes, into an approved class of medicines. Its commercial portfolio includes Amvuttra (vutrisiran) and Onpattro for transthyretin (TTR) amyloidosis, Givlaari for acute hepatic porphyria, and Oxlumo for a rare kidney disorder, plus royalties on Leqvio, an cholesterol-lowering RNAi drug marketed by partner Novartis. The defining event was the March 2025 FDA approval of Amvuttra for ATTR amyloidosis with cardiomyopathy (ATTR-CM), a far larger patient population than its earlier polyneuropathy indication, based on the HELIOS-B trial showing a 28% reduction in death and cardiac events.

Full ALNY guide

Silence Therapeutics plc is a London-headquartered biotechnology company built around short interfering RNA, a class of drug that switches off the production of a specific disease-causing protein in the liver rather than blocking it after the fact. Its proprietary discovery platform, marketed as mRNAi GOLD, attaches a GalNAc sugar to the siRNA so the molecule is taken up by liver cells, which is the same delivery approach behind the approved RNAi drugs on the market today. Two candidates carry the story. Zerlasiran silences the LPA gene to lower lipoprotein(a), an inherited cardiovascular risk factor with no approved therapy, and produced reductions of more than 80 percent in its Phase 2 ALPACAR-360 trial. Divesiran targets TMPRSS6 to raise hepcidin and control red blood cell production in polycythemia vera, a chronic blood cancer whose patients are otherwise managed with repeated therapeutic phlebotomy. A third asset, SLN312, was returned to Silence in March 2026 after AstraZeneca elected not to advance it past Phase 1.

Full SLN guide

Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.

• ALNY drivers: Amvuttra ATTR-CM ramp; Crossing into sustained profitability.
• SLN drivers: Divesiran and the SANRECO Phase 2 readout; A partner for zerlasiran.

A faster-growing, richer-valued name usually swings harder, so it suits a longer horizon and a higher tolerance for volatility; a steadier, more cash-generative business suits a more conservative or income-minded investor. The honest test is which set of risks you could hold through a drawdown: Revenue is heavily concentrated in the TTR franchise, so any competitive share loss or reimbursement setback for Amvuttra would hit the whole story. For SLN, silence generates essentially no product revenue, so the equity is a claim on clinical outcomes and financing terms rather than on earnings.

Growth-minded investors who believe the theme has years to run tend to accept the richer multiple for more upside; value-minded investors lean toward the cheaper forward earnings and steadier profile. Pick ALNY if you believe its drivers more; SLN if you believe its. Many investors hold both, but since they share themes, that is a concentrated bet, not diversification. Decide deliberately and check overlap. For the full detail, see the ALNY and SLN guides.

ALNY. Alnylam reached profitability in 2025 after nearly $3 billion in net product revenue, and Q1 2026 delivered about $1.0 billion in net product revenue with roughly $206 million of net income. At a market cap near $42 billion against 2026 revenue guidance of roughly $5 billion, the stock carries a premium multiple that prices in continued rapid growth. It pays no dividend and reinvests cash into its RNAi pipeline.

SLN. Conventional valuation multiples do not apply here: with trailing revenue under $1 million, a price-to-sales or price-to-earnings figure would be arithmetic noise. What the roughly $565 million market cap actually represents is about $72 million of cash plus a market-assigned value of roughly half a billion dollars for divesiran, zerlasiran and the platform behind them. Enterprise value therefore sits near $490 million, which is the number worth comparing against the probability-weighted commercial case for a polycythemia vera drug and a partnered lipoprotein(a) drug.

Headline figures (approximate, JULY 2026): ALNY shows market cap ~$42B, net product revenue (fy2025) ~$3.0B, net product revenue (ttm) ~$3.5B, 2026 revenue guidance ~$4.9B to $5.3B; SLN shows market cap ~$565M, revenue (ttm) ~$0.6M (collaboration revenue only, down from ~$42M in FY2024), net loss (ttm) ~$60M, cash and short-term investments (june 30, 2026) ~$72M.

ALNY and SLN are related but distinct: same themes, different businesses and risks. Neither wins in the abstract; the right pick is whichever thesis you actually believe, sized so you are not over-concentrated in one theme. Walnut can show your combined ALNY and SLN exposure against your real portfolio. It is not an investment adviser.