Company: MIRM
Filing Date: 2025-08-12
Form Type: S-3ASR
Source: 0001193125-25-178937
Chunk: 41

Company: Mirum Pharmaceuticals, Inc.
Filing Date: 2025-08-12
Form: S-3ASR
Chunk 41
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 Partners and Cantor. In connection with the sale of the common stock on our behalf, each of Leerink Partners and Cantor will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation of Leerink Partners and Cantor will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification and contribution to Leerink Partners and Cantor with respect to certain liabilities, including liabilities under the Securities Act or the Securities Exchange Act of 1934, as amended, or the Exchange Act. Investing in our common stock involves a high degree of risk. Please read the information contained in and incorporated by reference under the heading “ Risk Factors” beginning on page S-6of this prospectus supplement, and under similar headings in the other documents that are filed after the date hereof and incorporated by reference into this prospectus supplement and the accompanying prospectus. Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

| Leerink Partners |     | Cantor |

The date of this prospectus supplement is August 12, 2025.

TABLE OF CONTENTS PROSPECTUS SUPPLEMENT

|                                                   |     | Page |      |
| ABOUT THIS PROSPECTUS SUPPLEMENT                  |     |      | S-1  |
| PROSPECTUS SUPPLEMENT SUMMARY                     |     |      | S-2  |
| RISK FACTORS                                      |     |      | S-6  |
| FORWARD-LOOKING STATEMENTS                        |     |      | S-8  |
| USE OF PROCEEDS                                   |     |      | S-10 |
| DILUTION                                          |     |      | S-11 |
| PLAN OF DISTRIBUTION                              |     |      | S-13 |
| LEGAL MATTERS                                     |     |      | S-15 |
| EXPERTS                                           |     |      | S-15 |
| WHERE YOU CAN FIND MORE INFORMATION               |     |      | S-15 |
| INCORPORATION OF CERTAIN INFORMATION BY REFERENCE |     |      | S-16 |

S-i

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus relate to the offering of our common stock having an aggregate offering price of up
to $200,000,000 under the sales agreement.