MIRM vs REGN: Which Is the Better Buy in 2026?
Last updated August 2026
Short answer
REGN is the larger of the two ($78.52B market cap): the incumbent the market prices for continued execution (12.78x forward earnings, beta 0.24). MIRM is the smaller challenger ($5.74B), priced similarly on forward earnings (-500.61x): more room to run, but more to prove. The real question is which set of drivers you believe, and whether owning one (or both) leaves you over-concentrated.
MIRM vs REGN: the tie-breaker metrics
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.
| Metric | MIRM | REGN | What it tells you |
|---|---|---|---|
| Market cap | $5.74B | $78.52B | Size. The larger name is the incumbent; the smaller has more room to grow and more to prove. |
| Forward P/E | -500.61 | 12.78 | Valuation on next year's expected earnings, the same yardstick for both. Lower is cheaper for that growth; higher means the market is paying up. |
| Beta | 0.51 | 0.24 | Volatility vs the market. Above 1 swings harder than the index; below 1 is steadier. Higher beta means bigger drawdowns to hold through. |
| Price vs 52-week range | 52% of range | 79% of range | Where today's price sits between the 52-week low and high. Near the high is momentum with less margin of safety; near the low is out of favor or a discount, depending on why. |
| Price / book | 15.52 | 2.47 | How much you pay over book value. Very high can signal an asset-light, high-return business or a rich price. |
Before you buy: how MIRM and REGN affect your concentration
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. MIRM and REGN 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 MIRM and REGN 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.
What does Mirum Pharmaceuticals, Inc. (MIRM) do?
Mirum Pharmaceuticals develops and sells medicines for rare liver and metabolic diseases, conditions that affect small patient populations but have almost no alternatives. Three products carry the revenue. LIVMARLI (maralixibat) is an ileal bile acid transporter inhibitor approved for Alagille syndrome and progressive familial intrahepatic cholestasis, and it did about $128.7 million in the second quarter of 2026, up roughly 46% year over year. CHOLBAM (cholic acid) treats bile-acid synthesis disorders, and CTEXLI (chenodiol), approved in early 2025, is the first and only therapy specifically cleared for cerebrotendinous xanthomatosis in adults. Those two are reported together as bile acid medicines and contributed about $47.5 million in the quarter, up roughly 20%. Total net product sales reached about $176.2 million in Q2 2026, a gain of roughly 38%, and management raised full-year 2026 guidance to $680 million to $700 million after starting the year at $630 million to $650 million.
What does Regeneron Pharmaceuticals (REGN) do?
Regeneron makes money primarily through two large franchises. Dupixent, an anti-inflammatory antibody used for eczema, asthma, COPD, and other conditions, is developed and commercialized in collaboration with Sanofi, and Regeneron records its share through Sanofi collaboration revenue (about $1.6 billion in Q1 2026, up roughly 36%). Eylea and the higher-dose Eylea HD treat retinal diseases such as wet age-related macular degeneration and diabetic eye disease, generating combined U.S. net product sales of about $941 million in Q1 2026, with Eylea HD now roughly half of that mix. Libtayo in oncology and a pipeline of nearly 50 clinical candidates round out the revenue base.
MIRM vs REGN: how do they differ?
Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.
- MIRM drivers: LIVMARLI compounding in two approved indications; CTEXLI as a second growth engine.
- REGN drivers: Dupixent keeps compounding; A deep, diversified pipeline.
Which fits which kind of investor
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: The August 2026 volixibat decision is the clearest illustration of the risk: a Phase 2b study met its primary endpoint and had Breakthrough Therapy designation, and the FDA still recommended a full Phase 3, pushing an NDA to the first half of 2027 and knocking roughly 10% to 15% off the stock in a session. For REGN, the clearest risk is Eylea biosimilar erosion.
MIRM or REGN: which should you pick?
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 MIRM if you believe its drivers more; REGN 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 MIRM and REGN guides.
MIRM vs REGN: the full fundamentals
MIRM. Earnings multiples do not work on this name right now. The roughly $726 million in-process R&D charge from the Bluejay acquisition pushed trailing net loss to about $860 million, and the Q2 2026 loss was about $67.2 million, or $(1.06) a diluted share, so investors generally value Mirum on revenue and pipeline probability instead. At roughly 8 to 9 times sales the market is paying a growth-biotech multiple for a business compounding above 40%, which means a meaningful share of the price rests on programs that are not yet approved. Beta runs near 0.5, low for a biotech, because the stock moves on regulatory news rather than with the broad market.
REGN. Figures are approximate and tied to the asOf date; verify current numbers with a live quote before acting. Regeneron reported about 19% revenue growth and adjusted EPS of roughly $9.47 in Q1 2026, beating estimates, and authorized an additional $3 billion buyback. The mid-teens P/E reflects the market weighing strong Dupixent growth against expected Eylea biosimilar erosion.
Headline figures (approximate, August 2026): MIRM shows net product sales (ttm) ~$618 million, up ~44% year over year, q2 2026 product sales ~$176.2 million, up ~38%, with LIVMARLI ~$128.7 million and bile acid medicines ~$47.5 million, 2026 guidance ~$680 million to $700 million, raised from ~$660 million to $680 million, r&d expense (q2 2026) ~$90.5 million, against SG&A of ~$81.5 million; REGN shows total revenue (ttm, approx) ~$14 billion, q1 2026 total revenue ~$3.6 billion (up ~19% YoY), dupixent global net sales (q1 2026) ~$4.9 billion (up ~31%), eylea + eylea hd u.s. net sales (q1 2026) ~$941 million combined.
The bottom line: MIRM vs REGN
MIRM and REGN 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 MIRM and REGN exposure against your real portfolio. It is not an investment adviser.
Wondering how MIRM or REGN fits the portfolio you already own? Walnut is an AI investing app that connects your brokerage read-only and answers questions like that about your actual holdings: overlap, concentration, and how each position tracks the S&P 500. Compare the best AI portfolio analyzers or see the best AI investing apps in 2026.
Investing in Mirum Pharmaceuticals, Inc. with AI
Connect the broker you already use and ask Walnut's AI how MIRM fits what you actually hold: whether you own it already through a fund, what it would do to your concentration, and how it has tracked the S&P 500. Read-only by default, and you approve anything before it reaches your broker.
FAQ
What is the difference between MIRM and REGN?
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Mirum Pharmaceuticals develops and sells medicines for rare liver and metabolic diseases, conditions that affect small patient populations but have almost no alternatives. Regeneron makes money primarily through two large franchises. They show up together because they share investment themes, but they are different businesses, so the better fit depends on which thesis you are expressing.
Is MIRM or REGN the better stock?
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Neither is universally better. REGN is the larger incumbent; MIRM is the smaller challenger and looks cheaper on forward earnings. Walnut is informational, not investment advice. Compare what each does, the tie-breaker metrics above, and the risks, then decide which fits your thesis and what you already own.
Which is cheaper, MIRM or REGN?
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On forward P/E (as of August 2026), MIRM trades at -500.61x and REGN at 12.78x, so MIRM is the cheaper of the two on next year's expected earnings. A lower multiple is not automatically the better buy: a richer valuation can be justified by faster growth, and a lower one can reflect real risk. Weigh the multiple against how fast each business is compounding.
Should you own both MIRM and REGN?
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Because they share themes, owning both concentrates you in that theme. That can be intentional (a focused bet) or accidental (less diversification than it looks). Walnut can show your combined exposure across both, and whether adding either over-concentrates you, before you buy.
What are the risks of MIRM vs REGN?
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MIRM: The August 2026 volixibat decision is the clearest illustration of the risk: a Phase 2b study met its primary endpoint and had Breakthrough Therapy designation, and the FDA still recommended a full Phase 3, pushing an NDA to the first half of 2027 and knocking roughly 10% to 15% off the stock in a session. Reported profitability is deeply negative because of the roughly $726 million in-process R&D charge from the Bluejay acquisition, so trailing GAAP earnings and price-to-earnings screens are effectively meaningless here and any valuation work has to run off revenue and cash. Revenue is concentrated: LIVMARLI alone is roughly three quarters of product sales, and it competes directly with Ipsen's Bylvay in the same small patient populations, where a payer formulary decision or a safety label change can move share quickly. Rare-disease pricing carries persistent policy and reimbursement exposure, and the addressable populations are measured in thousands of patients rather than millions, so a single failed diagnosis-expansion effort matters. The zilurgisertib and brelovitug programs are unapproved assets purchased or licensed at real cost, and neither has generated a dollar of revenue. REGN: The clearest risk is Eylea biosimilar erosion. Amgen's Pavblu launched in late 2024 and pressured sales, and settlements clear paths for Sandoz, and Alvotech and Teva, to launch competing copies in the U.S. around the fourth quarter of 2026, with erosion expected to accelerate. Eylea HD and Dupixent growth are the offsets, but the timing gap matters. The business is also concentrated in a few franchises, so a single setback in Dupixent or a major pipeline failure would weigh heavily, and the collaboration structure with Sanofi means Regeneron does not control all of its largest product's economics.
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Walnut is informational, not investment advice. This page is descriptive and not a recommendation to buy or sell MIRM or REGN; figures are approximate and dated (as of August 2026). Verify current data before investing.