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WARNING LETTER

November 12, 2025

RE: 718720

Hyun-Kwang Dan:

This letter is to advise you that on April 15, 2025, the U.S. Food and Drug Administration (FDA) reviewed your product labeling, including your website at www.sinsinpas.us/, which directs consumers to your Amazon storefront where your SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS drug products are available for purchase in the United States without a prescription. We also reviewed your social media on Facebook and Instagram at https://www.facebook.com/search/top?q=sinsinpas_us and https://www.instagram.com/sinsinpas_us, which also direct consumers to your Amazon storefront.

SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS are unapproved new drugs introduced or delivered for introduction into interstate commerce in violation of sections 505(a) and 301(d) of the Federal Food, Drug, and Cosmetic Act (FD&C Act), 21 U.S.C. 355(a), 331(d). In addition, these products are misbranded under section 502(ee) of the FD&C Act, 21 U.S.C. 352(ee). Introduction or delivery for introduction of misbranded products into interstate commerce is prohibited under section 301(a) of the FD&C Act, 21 U.S.C. 331(a). These violations are described in more detail below.

Unapproved New Drug and Misbranded Drug Violations

SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS are drugs as defined by section 201(g)(1)(B) of the FD&C Act, 21 U.S.C. 321(g)(1)(B), because they are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease, and/or under section 201(g)(1)(C) of the FD&C Act, 21 U.S.C. 321(g)(1)(C), because they are intended to affect the structure or any function of the body.

Examples from the SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS product labeling, including your website listed above, that provide evidence of the intended uses (as defined in 21 CFR 201.128) of the product as a drug include, but may not be limited to, the following:

SINSINPAS AREX INSTANT PAIN RELIEF
“Drug Facts . . . Purpose: Topical Analgesic . . . Uses For temporary relief of minor aches and pains of muscles and joints associated with: ■ Arthritis ■ Simple Backache ■ Strains ■ Bruises ■ Sprains,” “- Joint Pain – Muscle pain – Sprains – Backache” [from the product label]

SINSINPAS Pain Relieving Liquid MULPAS
“Drug Facts . . . Purpose: Topical Analgesic . . . Uses For temporary relief of minor aches and pains associated with: ■ arthritis ■ simple backache ■ sprains ■ strains ■ bruises” ; “Muscle Pain Arthritis Strains Insect Bites” [from the product label]

Unapproved New Drug Violations

Based on the above labeling evidence SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS are intended for use as external analgesic drug products. As described below, these drug products are unapproved new drugs marketed in violation of sections 505(a) and 301(d) of the FD&C Act, 21 U.S.C. 355(a) and 331(d).

A drug product is a “new drug” within the meaning of section 201(p) of the FD&C Act, 21 U.S.C. 321(p), if it is not generally recognized as safe and effective (GRASE) for use under the conditions prescribed, recommended, or suggested in its labeling. With certain exceptions not applicable here, a new drug may not be introduced or delivered for introduction into interstate commerce without an approved application from FDA in effect, as described in section 505(a) of the FD&C Act, 21 U.S.C. 355(a). No FDA-approved applications pursuant to section 505 of the FD&C Act, 21 U.S.C. 355, are in effect for these drug products identified above.

Under section 505G of the FD&C Act, certain nonprescription drugs marketed without an approved application —commonly referred to as “over-the-counter (OTC) monograph drugs”—may be legally marketed if they meet applicable requirements. With respect to nonprescription external analgesic drug products, such as your SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS, in order to be GRASE and not new drugs, the products must, among other things, conform to the conditions in the applicable OTC monograph, here External Analgesic Drug Products for Over-the-Counter Human Use (hereafter M017).¹ However, SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS do not conform to the conditions specified in M017 for the reasons described below.

Your SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS are formulated with active ingredients that are not permitted for OTC external analgesic drug products under M017.12. Specifically, according to your product’s labeling, your SINSINPAS AREX INSTANT PAIN RELIEF product is formulated with the active ingredients zinc oxide and mentha oil. However, zinc oxide and mentha oil are not permitted active ingredients under M017.12 when used in combination, or as sole ingredients, for any OTC external analgesic drug product.

In addition, your SINSINPAS Pain Relieving Liquid MULPAS is formulated with the active ingredients chlorpheniramine maleate and thymol. However, chlorpheniramine maleate and thymol are not permitted active ingredients under M017.12 when used in combination, or as sole ingredients, for any OTC external analgesic drug product. Furthermore, FDA has also determined that OTC external analgesic and anesthetic drug products with the active ingredient thymol are not generally recognized as safe and effective (GRASE) under a final determination issued under 21 CFR par 330.²

Thus, your SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS products do not comply with the applicable conditions specified in M017 and have not otherwise been found GRASE.³ Accordingly, these products are new drugs within the meaning of section 201(p) of the FD&C Act, 21 U.S.C. 321(p), and there is no basis under section 505G of the FD&C Act under which these products would be legally marketed without an approved application. Because there are no approved applications in effect for these products, these products are unapproved new drugs. The introduction or delivery for introduction into interstate commerce of these unapproved new drug products violates sections 505(a) and 301(d) of the FD&C Act, 21 U.S.C. 355(a) and 331(d).

Misbranded Drug Violations

Additionally, SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS are misbranded under section 502(ee) of the FD&C Act, 21 U.S.C. 352(ee), because these products are nonprescription drugs subject to section 505G of the FD&C Act, 21 U.S.C. 355h, but do not comply with the requirements for marketing under that section and are not the subject of an application approved under section 505 of the FD&C Act, 21 U.S.C. 355.

The introduction or delivery for introduction of a misbranded drug into interstate commerce violates section 301(a) of the FD&C Act, 21 U.S.C. 331(a).

Conclusion

The violations cited in this letter are not intended to be an all-inclusive list of violations that may exist in connection with your products. You are responsible for investigating and determining the causes of any violations and for preventing their recurrence or the occurrence of other violations. It is your responsibility to ensure that your firm complies with all requirements of federal law, including FDA regulations.

This letter notifies you of our concerns and provides you an opportunity to address them. Failure to adequately address this matter may result in legal action including, without limitation, seizure and injunction.

Please notify FDA in writing, within 15 working days of receipt of this letter, of the specific steps you have taken to correct any violations. Include an explanation of each step being taken to prevent the recurrence of violations, as well as copies of related documentation. If you believe that your products are not in violation of the FD&C Act, include your reasoning and any supporting information for our consideration. If you cannot complete corrective action within 15 working days, state the reason for the delay and the time within which you will complete the correction. Your response should be sent to U.S. Food and Drug Administration, CDER/OC/Office of Unapproved Drugs and Labeling Compliance by email to FDAAdvisory@fda.hhs.gov. Please include your firm name and the unique identifier “718720” in the subject line of the email.

Sincerely,
/S/

Tina Smith, M.S.
Captain, U.S. Public Health Service
Director
Office of Unapproved Drugs and Labeling Compliance
Office of Compliance
Center for Drug Evaluation and Research
U.S. Food and Drug Administration

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1 M017 reflects the conditions as set forth in the relevant final orders established and in effect under section 505G; see Order OTC000033, available at FDA’s website OTC Monographs@FDA https://dps.fda.gov/omuf.

2 Non-Monograph Conditions NM900: Drug Products Containing Certain Active Ingredients Offered Over-the-Counter for Certain Uses. See Order ID OTC000007, available at FDA’s website OTC Monographs@FDA, https://dps.fda.gov/omuf.

3 FDA is not aware of any adequate and well-controlled clinical trials in the published literature that support a determination that SINSINPAS AREX INSTANT PAIN RELIEF and SINSINPAS Pain Relieving Liquid MULPAS are GRASE for use under the conditions prescribed, recommended, or suggested in their labeling, nor has FDA determined these drug products to be GRASE pursuant to an order issued under section 505G(b).