Sec Form 3 Filing - Shafer Christina @ MARINUS PHARMACEUTICALS, INC. - 2022-06-15

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Shafer Christina 2. Issuer Name and Ticker or Trading Symbol MARINUS PHARMACEUTICALS, INC. [ MRNS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Commercial Officer (Last) (First) (Middle) 5 RADNOR CORP CENTER SUITE 500, 100 MATSONFORD RD 3. Date of Earliest Transaction (MM/DD/YY) 06/15/2022 (Street) RADNOR, PA19087 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 27,152( 1 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Option (Right to Buy) $ 13.71 ( 2 ) 11/09/2030 Common Stock 128,000 D Stock Option (Right to Buy) $ 12.6 ( 3 ) 01/15/2031 Common Stock 15,000 D Stock Option (Right to Buy) $ 10.4 ( 4 ) 02/04/2032 Common Stock 57,900 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Shafer Christina 5 RADNOR CORP CENTER SUITE 500 100 MATSONFORD RD RADNOR, PA19087 Chief Commercial Officer Signatures /s/Debra A. Mohollen, Attorney-in-Fact 06/23/2022 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes: (i) 10,000 shares of restricted stock granted on November 9, 2020, of which 5,000 vested on November 9, 2021 and 1,505 of those shares were withheld to cover taxes, and the remaining 5,000 RSAs will vest on November 9, 2022, subject to the reporting person's continued service with the Issuer, (ii) 12,867 restricted stock units (RSUs) granted on February 4, 2022 that vest in three equal installments, with the first installment vesting on August 4, 2023, the second installment vesting on August 4, 2024, and the third installment vesting on August 4, 2024, subject to the reporting person's continued service with the Issuer, and (iii) 5,790 RSUs granted on May 24, 2022 that vest in two equal installments with the first installment vesting on August 4, 2023, and the second installment vesting on August 4, 2024, subject to the reporting person's continued service with the Issuer. Each RSU represents the right to receive one share of common stock of the Issuer. ( 2 )An option to purchase 128,000 shares of common stock of the Issuer was granted on November 9, 2020, of which 25%, or 32,000 shares, vested and became exercisable on November 9, 2021 and the remaining shares underlying the option began vesting in 36 equal monthly installments on December 9, 2021. ( 3 )An option to purchase 15,000 shares of common stock of the Issuer was granted on January 15, 2021. The shares underlying the option began vesting in 36 equal monthly installments on January 31, 2021. ( 4 )An option to purchase 57,900 shares of common stock of the Issuer was granted on February 4, 2022. The shares underlying the option began vesting in 36 equal monthly installments on March 4, 2022.

Remarks: Exhibit 24- Power of Attorney

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