Gavin Newsom has signed legislation restricting the sale of certain muscle building supplements and diet products to Californians under 18. The measure focuses on products marketed for weight loss or building muscle rather than imposing a blanket prohibition on every supplement containing particular ingredients.

The legislation, AB 2030, was signed on Sept. 28 and will take effect on Jan. 1, 2027. It covers over the counter diet pills and dietary supplements promoted for weight loss or muscle building.

Under the law, restrictions apply to products “labeled, marketed or otherwise represented for the purpose of achieving weight loss or building muscle.” That language makes the presentation and promotion of a supplement central to whether its sale to minors is restricted.

The governor’s office warned that products sold without prescriptions or medical approval can present risks. “Nonprescribed, medically unapproved products may cause dangerous side effects,” the office said in its announcement. “Products can be mislabeled or contaminated with substances such as steroids.”

Courts may consider whether a product contains creatine, green tea extract, raspberry ketone, garcinia cambogia or green coffee bean extract, according to the legislation. The presence of one of those ingredients, however, does not automatically create an outright prohibition.

The law does not ban all creatine products. Restrictions instead depend on how a supplement is labeled, advertised and marketed, while the announcement does not specify whether whey protein or creatine products are included.

An exception applies when a person under 18 has a prescription for an over the counter diet pill or a dietary supplement intended for weight loss or muscle building. The law therefore allows prescribed access to products that might otherwise fall under its sales restrictions.

The governor’s release cites research indicating that nearly one in 10 adolescents have used these types of products. It also points to studies associating over the counter diet pill use with a sixfold greater likelihood of receiving an eating disorder diagnosis within three years.

Businesses that fail to comply with the new requirements may face civil fines of up to $500 for each violation. The financial penalty places responsibility on sellers to determine whether covered products can legally be sold to customers under 18.

The American Herbal Products Association, an organization based in Maryland, issued a statement opposing the measure. The association challenged the law’s scientific basis and raised concerns about the breadth and clarity of its restrictions.

“Lacking any scientific justification, AB 2030 casts a shadow over safe, beneficial products,” Robert Marriott, the association’s vice president of regulatory and government affairs, said in the statement. His organization also noted that protein products are not explicitly exempted.

The association argues that the scope of AB 2030 is unclear. That concern centers on which products will ultimately be covered when marketing, labeling, ingredients and representations to consumers are considered together.

The Center for Science in the Public Interest, based in Washington, D.C., publicly supported the legislation and helped sponsor it. “Manufacturers of these products often prey on kids and teens with deceptive claims that lack any scientific evidence,” said Jensen Jose, a regulatory counsel at the organization.

Dr. Sigrid Wolf, a pediatric sports medicine physician at Lurie Children’s Hospital of Chicago, recently discussed creatine use among teenagers and said evidence of benefits is limited. Wolf is a member of the American Academy of Pediatrics’ sports medicine committee.

“In some cases, they might even be dangerous,” Wolf wrote in an article published on HealthyChildren.org, the American Academy of Pediatrics’ parenting website. “Creatine can come with negative side effects such as weight gain , dizziness, nausea, vomiting and diarrhea.”

“Studies show that many supplements contain harmful substances that go undetected,” Wolf added. She recommended that teenagers prioritize nutrition, training, sleep and hydration, while Fox News Digital reached out to Newsom’s office for comment.