MediciNova : Form of prospectus disclosing information, facts, events covered in both forms 424B2, 424B3

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Filed Pursuant to Rule 424(b)(5)

Registration No. 333-233201

PROSPECTUS SUPPLEMENT

(to the Prospectus dated August 22, 2019)

$75,000,000

Common Stock

We have entered into an at market issuance sales agreement, or sales agreement, with B. Riley FBR, Inc., or B. Riley FBR, relating to shares of our common stock offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the sales agreement, we may offer and sell shares of our common stock, $0.001 par value per share, having an aggregate offering price of up to $75,000,000 from time to time to and/or through B. Riley FBR, as sales agent or principal, pursuant to this prospectus supplement and the accompanying prospectus.

Our common stock is listed on The NASDAQ Global Market under the symbol "MNOV" and on the Jasdaq Market of the Tokyo Securities Exchange under the code "4875." The last reported sale price of our common stock on The NASDAQ Global Market on August 22, 2019 was $8.81 per share.

Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be made in sales deemed to be "at the market offerings" as defined in Rule 415 promulgated under the Securities Act of 1933, as amended (the "Securities Act"). B. Riley FBR will act as a sales agent on a best efforts basis using commercially reasonable efforts consistent with its normal trading and sales practices, on mutually agreed terms between B. Riley FBR and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

The compensation to B. Riley FBR for sales of common stock sold pursuant to the sales agreement will be up to 3.5% of the gross proceeds from each sale. We have also agreed to reimburse B. Riley FBR for certain of its expenses. In connection with the sale of the common stock on our behalf, B. Riley FBR will be deemed to be an "underwriter" within the meaning of the Securities Act, and the compensation of B. Riley FBR will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification and contribution to B. Riley FBR with respect to certain liabilities, including liabilities under the Securities Act. See "Plan of Distribution" for more information about these arrangements.

Before buying shares of our common stock, you should carefully consider the risk factors described in "Risk Factors" beginning on page S-7 of this prospectus supplement and page 5 of the accompanying prospectus, 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 state securities commission has approved or disapproved of these securities or determined if this prospectus supplement and the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

B. Riley FBR

The date of this prospectus supplement is August 23, 2019.

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TABLE OF CONTENTS
Prospectus Supplement	Page
ABOUT THIS PROSPECTUS SUPPLEMENT	S-1
PROSPECTUS SUPPLEMENT SUMMARY	S-2
THE OFFERING	S-6
RISK FACTORS	S-7
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	S-8
USE OF PROCEEDS	S-10
DILUTION	S-11
PLAN OF DISTRIBUTION	S-12
LEGAL MATTERS	S-14
EXPERTS	S-14
WHERE YOU CAN FIND MORE INFORMATION	S-14
INFORMATION INCORPORATED BY REFERENCE	S-15
Prospectus	Page
ABOUT THIS PROSPECTUS	1
PROSPECTUS SUMMARY	2
RISK FACTORS	5
FORWARD-LOOKING STATEMENTS	5
USE OF PROCEEDS	6
DESCRIPTION OF SECURITIES WE MAY OFFER	7
DESCRIPTION OF CAPITAL STOCK	7
DESCRIPTION OF DEBT SECURITIES AND GUARANTEES	13
DESCRIPTION OF WARRANTS	26
DESCRIPTION OF UNITS	28
LEGAL OWNERSHIP OF SECURITIES	29
PLAN OF DISTRIBUTION	32
LEGAL MATTERS	35
EXPERTS	35
WHERE YOU CAN FIND MORE INFORMATION	35
INFORMATION INCORPORATED BY REFERENCE	36
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ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is the prospectus supplement, including the documents incorporated by reference, which describes the specific terms of this offering. The second part, the accompanying prospectus, including the documents incorporated by reference, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. We urge you to carefully read this prospectus supplement and the accompanying prospectus, and the documents incorporated herein and therein, before buying any of the securities being offered under this prospectus supplement. This prospectus supplement may add to, update or change information contained in the accompanying prospectus. To the extent that any statement that we make in this prospectus supplement is inconsistent with statements made in the accompanying prospectus or any documents incorporated by reference therein, the statements made in this prospectus supplement will be deemed to modify or supersede those made in the accompanying prospectus and such documents incorporated by reference therein. You should also read and consider the information contained in the documents identified under the headings "Incorporation of Certain Documents by Reference" and "Where You Can Find More Information."

You should rely only on the information contained in, or incorporated by reference into, this prospectus supplement, and the accompanying prospectus. We have not, and B. Riley FBR has not, authorized anyone to provide you with different information. No dealer, salesperson or other person is authorized to give any information or to represent anything not contained in this prospectus supplement and the accompanying prospectus. You should not rely on any unauthorized information or representation. This prospectus supplement is an offer to sell only the securities offered hereby, and only under circumstances and in jurisdictions where it is lawful to do so. You should assume that the information in this prospectus supplement and the accompanying prospectus is accurate only as of the date on the front of the applicable document and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus supplement or the accompanying prospectus, or any sale of a security.

This prospectus supplement, the accompanying prospectus, and the information incorporated herein and therein by reference includes trademarks, service marks and trade names owned by us or other companies. All trademarks, service marks and trade names included or incorporated by reference into this prospectus supplement or the accompanying prospectus are the property of their respective owners.

All references in this prospectus supplement and the accompanying prospectus to "MediciNova," the "Company," "we," "us," "our," or similar references refer to MediciNova, Inc., a Delaware corporation, and its subsidiaries on a consolidated basis, except where the context otherwise requires or as otherwise indicated.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information contained elsewhere in or incorporated by reference into this prospectus supplement. This summary is not complete and does not contain all of the information that you should consider before deciding whether to invest in our securities. For a more complete understanding of our company and this offering, we encourage you to read and consider carefully the more detailed information in this prospectus supplement and the accompanying prospectus, including the information incorporated by reference into this prospectus supplement and the accompanying prospectus, and the information included in any free writing prospectus that we have authorized for use in connection with this offering. If you invest in our securities, you are assuming a high degree of risk. See "Risk Factors."

About MediciNova, Inc.

Our Business

We are a biopharmaceutical company focused on acquiring and developing novel, small molecule therapeutics for the treatment of serious diseases with unmet medical needs and a commercial focus on the U.S. market. Our current strategy is to focus our development activities on MN-166 (ibudilast) for neurological disorders such as progressive multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), chemotherapy- induced peripheral neuropathy, degenerative cervical myelopathy, glioblastoma, and substance dependenc and addiction (e.g., methamphetamine dependence, opioid dependence, and alcohol dependence), and MN-001 (tipelukast) for fibrotic diseases such as nonalcoholic steatohepatitis (NASH) and idiopathic pulmonary fibrosis (IPF). Our pipeline also includes MN-221 (bedoradrine) for the treatment of acute exacerbation of asthma and MN-029 (denibulin) for solid tumor cancers.

MN-166 (ibudilast) is currently in development for several different neurological diseases as described below.

• Progressive Multiple Sclerosis: We completed a Phase 2b clinical trial of MN-166 (ibudilast) for the treatment of relapsing multiple sclerosis (MS), in which positive safety and neuroprotective efficacy indicators were observed. The data from this trial indicated that MN-166 (ibudilast) may have potential in the treatment of progressive MS.

We partnered with investigators on a Phase 2b clinical trial of MN-166 (ibudilast) in primary progressive and secondary progressive MS which was conducted by NeuroNEXT and funded by the National Institute of Health's (NIH) National Institute of Neurological Diseases and Stroke (NINDS). This progressive MS trial, known as SPRINT-MS, completed randomization of 255 subjects in 2015, which exceeded the goal of 250 subjects that were planned for participation. In October 2017, we announced the presentation of positive top-line results from the SPRINT-MS Phase 2b clinical trial of MN-166 (ibudilast) in progressive MS. The trial achieved both primary endpoints of whole brain atrophy and safety and tolerability. MN-166 (ibudilast) demonstrated a statistically significant 48% reduction in the rate of progression of whole brain atrophy compared to placebo (p=0.04) as measured by MRI analysis using brain parenchymal fraction (BPF) and there was not an increased rate of serious adverse events in the MN-166 (ibudilast) group compared to the placebo group. In February 2018, we announced the presentation of positive clinical efficacy trends from this trial regarding the important secondary endpoint of confirmed disability progression. MN-166 (ibudilast) demonstrated a 26% reduction in the risk of confirmed disability progression compared to placebo (hazard ratio = 0.74), as measured by EDSS (Expanded Disability Status Scale). Results of the SPRINT-MS Phase 2b clinical trial of MN-166 (ibudilast) in progressive MS were published in the New England Journal of Medicine in August 2018.

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The United States Food and Drug Administration (FDA) has granted Fast Track designation for the development of MN-166 (ibudilast) for the treatment of patients with progressive MS.

• Amyotrophic Lateral Sclerosis (ALS): We initiated a clinical trial of MN-166 (ibudilast) in amyotrophic lateral sclerosis (ALS) in the second half of 2014, and this trial was completed during the second half of 2017. In December 2017, we announced positive top-line results from this trial. The trial achieved the primary endpoint of safety and tolerability. In addition, there was a higher rate of responders on the ALSFRS-R total score in the MN-166 (ibudilast) group compared to the placebo group. The Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised(ALSFRS-R) total score measures the functional activity of an ALS subject. In July 2018, we announced data from ad-hoc subgroup analyses in ALS subjects who had either bulbar onset or upper limb onset. In September 2018, we received feedback from the FDA regarding our Phase 3 clinical development plan for MN-166 (ibudilast) in ALS. In January 2019, we received a Notice of Allowance from the U.S. Patent and Trademark Office for a pending patent application which covers the combination of MN-166 (ibudilast) and riluzole for the treatment of ALS and other neurodegenerative diseases.

We have collaborated with Massachusetts General Hospital (MGH) to conduct a clinical trial to study the effects of MN-166 (ibudilast) on reducing brain microglial activation in ALS subjects which can be monitored by a biomarker. This ongoing clinical trial, which we refer to as the ALS / Biomarker study, will also evaluate several clinical outcomes. In July 2018, we announced that the ALS / Biomarker study was fully enrolled.

The FDA has granted Fast Track designation to MN-166 (ibudilast) for the treatment of ALS as well as Orphan-Drug designation for the treatment of ALS, which will provide seven years of marketing exclusivity if it is approved for ALS. The European Commission also granted Orphan Medicinal Product Designation for MN-166 (ibudilast) for the treatment of ALS.

• Substance Dependence and Addiction: In the area of addiction, the National Institute on Drug Abuse (NIDA) funded a Phase 2 clinical trial studying the use of MN-166 (ibudilast) for the treatment of methamphetamine addiction. In collaboration with the University of California, Los Angeles (UCLA), this clinical trial commenced in 2013 and enrollment was completed in September 2017. In March 2018, we announced that this trial did not meet the primary endpoint of methamphetamine abstinence confirmed via urine drug screens during the final two weeks of treatment. In November 2017, we announced a collaboration with Oregon Health & Science University to initiate a biomarker study for evaluating MN-166 (ibudilast) in methamphetamine use disorder and this trial is ongoing.

Investigators at Columbia University and the New York State Psychiatric Institute (NYSPI) previously completed a Phase 1b/2a clinical trial of MN-166 (ibudilast) in opioid withdrawal that was funded by NIDA. Investigators at Columbia University and the NYSPI also conducted a NIDA-funded, Phase 2a clinical trial to evaluate the efficacy of MN-166 (ibudilast) in the treatment of patients addicted to prescription opioids or heroin. In March 2016, we announced that positive findings from the results of this completed study in opioid dependence were presented at the Behavior, Biology and Chemistry: Translational Research in Addiction Meeting.

Researchers at UCLA were granted approval and funding by the National Institute on Alcoholism and Alcohol Abuse (NIAAA) for a clinical trial to evaluate MN-166 (ibudilast) for the treatment of alcohol dependence. This clinical trial has been completed and results were presented at the American College of Neuropsychopharmacology (ACNP)'s 54th Annual Meeting in December 2015. In May 2018, we announced a new NIDA-funded clinical trial of MN-166 (ibudilast) in alcohol dependence and withdrawal in collaboration with researchers at UCLA and this trial is ongoing. In August 2018, we announced a new NIAAA-funded Phase 2b clinical trial of MN-166 (ibudilast) which will evaluate

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