Company: MIRM
Filing Date: 2025-08-12
Form Type: S-3ASR
Source: 0001193125-25-178937
Chunk: 48

Company: Mirum Pharmaceuticals, Inc.
Filing Date: 2025-08-12
Form: S-3ASR
Chunk 48
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 future issuance under our ESPP; and |

| • |     | 25,177 shares of our common stock reserved for issuance under our 2020 Inducement Plan, or Inducement Plan, as of 
 June 30, 2025.                                                                                                    |

Except as otherwise indicated, all information in this prospectus supplement assumes no exercise of outstanding options, no vesting of restricted stock units or performance stock units and no conversion of outstanding convertible notes after June 30, 2025 .

S-5

RISK FACTORS

Investing in our common stock involves a high degree of risk. Before making an investment decision, you should carefully consider the risks described below and in our most recent Annual Report on Form 10-Kand Quarterly Report on Form 10-Q,as updated or superseded by the risks and uncertainties described in our subsequent filings under the Exchange Act, each of which is incorporated by reference into this prospectus supplement and the accompanying prospectus in their entirety, and all of the other information in this prospectus supplement and the accompanying prospectus, including our financial statements and related notes incorporated by reference in this prospectus supplement and the accompanying prospectus. If any of these risks is realized, our business, financial condition, results of operations and prospects could be harmed. In that event, the trading price of our common stock could decline and you could lose part or all of your investment. Additional risks and uncertainties that are not yet identified or that we think are immaterial may also harm our business, operating results and financial condition and could result in a complete loss of your investment.

Risks Related to This Offering

We have broad discretion in the use of the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion in the application of the net proceeds to us from this offering and could spend the
proceeds in ways that do not improve our results of operations or enhance the value of our common stock. The failure by our management to apply these funds effectively could result in financial losses that could have a material adverse effect on our
business, cause the price of our common stock to decline and delay the development of our drug candidates. Pending their use, we may invest the net proceeds from this offering in short-term, investment-grade, interest-bearing instruments.

If you purchase shares of common stock in this offering, you will suffer immediate dilution of your investment.

The offering prices per share in this offering may exceed the net tangible book value per share of our common stock. Assuming that an aggregate