More than half of Californians and nearly 75% of U.S. residents live in communities where fluoride has been added to drinking water to prevent tooth decay, an intervention hailed by the U.S. Centers for Disease Control as one of the 20th century’s greatest public health achievements.

Yet should Donald Trump be elected to a second term, water systems will be immediately directed to end this practice, according to supporter Robert F. Kennedy Jr.

“On January 20, the Trump White House will advise all U.S. water systems to remove fluoride from public water,” Kennedy posted Saturday on the social media platform X.

Kennedy described the mineral, which occurs naturally in all fresh water supplies, as an “industrial waste” associated with a variety of health risks.

On Sunday, Trump told NBC News that he had not discussed the fluoride proposal with Kennedy, “but it sounds OK to me.” Reached for comment Monday, a campaign spokesperson told The Times that while Trump “has received a variety of policy ideas, he is focused on Tuesday’s election.”

Kennedy’s statement follows a September ruling from a federal judge in California that could have major effects on the long-standing public health intervention, but that multiple dentists and pediatricians say is based on a flawed reading of the available science.

In his X post, Kennedy tagged Michael Connett, the lead attorney representing the plaintiff in that lawsuit, the advocacy group Food & Water Watch.

In late September, U.S. District Judge Edward Chen ordered the U.S. Environmental Protection Agency to take further unspecified steps to regulate fluoride in drinking water.

In his ruling, Chen cited a literature review by the U.S. National Toxicology Program that found associations between exposure to high levels of fluoride and lower IQ levels in children.

Though he could not “conclude with certainty that fluoridated water is injurious to public health,” Chen wrote, he still determined that it posed an “unreasonable risk” of harm. His ruling did not specify what exactly the EPA should do about that.

The American Dental Assn. and American Academy of Pediatrics issued a joint statement of concern after the ruling, saying that there were major limitations in the study Chen cited. The groups pointed out that the study found low IQ associations only at fluoride concentrations more than double those of the current recommendation of 0.7 milligrams per liter.

“There is nothing about the current decision that changes my confidence in the safety of optimally fluoridated water in the U.S.,” said Dr. Charlotte W. Lewis, a member of the AAP Section on Oral Health, at the time. “Water fluoridation is a public health policy based on a solid foundation of evidence.”

In California, scientifically shaky skepticism of fluoridated water has been around almost as long as the stuff has been coming out of the taps.

In 1952, San Francisco and Antioch became the first communities in California to supplement naturally occurring levels of fluoride in their drinking water, after a raft of studies showing that the mineral made teeth enamel stronger and more resistant to acid. Within a decade, cavities in 6-year-olds’ permanent teeth had dropped by 84%.

The U.S. Public Health Service in 1962 recommended a fluoridation level of 0.7 to 1.2 mg per liter in drinking water supplies. (In 2015 the service revised its recommendation to 0.7 mg per liter — a sweet spot that maximized the dental health advantages while reducing the risk of tooth discoloration associated with excess fluoride exposure.)

Yet as the number of communities in California voting to fluoridate their water grew, so did complaints from skeptics who pushed debunked theories about fluoride’s link to cancer, AIDS and other conditions, according to a history by UC San Francisco oral biology professor Ernest Newburn.

Despite California’s early leadership in water fluoridation, it now ranks 39th among U.S. states in the percentage of the population covered by fluoridated water systems, with 57.5% of residents living in covered communities, according to the United Health Foundation. (Kentucky leads the board with 99.9% coverage.)

An exploratory study published this year found associations between prenatal exposure to fluoride and an increased risk of neurobehavioral problems at age 3 in a cohort of 229 Los Angeles-area children.

The American Dental Assn., the American Academy of Pediatrics and others have pushed back on the study, citing concerns about the methods used to evaluate both child IQ and maternal fluoride levels.

“It is irresponsible of the authors, based on this study, to suggest that recommendations be changed on the beneficial use of fluoride to prevent dental problems,” said Howard Pollick, a professor at the UC San Francisco School of Dentistry, shortly after the study was published.

A larger study published last year followed more than 2,000 children in Australia over five years and found no associations between prenatal fluoride exposure and behavioral development problems.

Both Trump and Kennedy have said publicly that longtime anti-vaccine activist Kennedy will probably have a prominent role in health policy in a second Trump administration.

“I’m gonna let him go wild on health. I’m gonna let him go wild on the food. I’m gonna let him go wild on medicines,” Trump told supporters during a rally at Madison Square Garden last month.

The Associated Press contributed to this report.

Shauna Bookless never imagined she’d become her own pharmacist. But after gaining more than 20 pounds during undergraduate and graduate school and feeling unhappy with her weight, the Hollywood resident found herself mixing vials in her kitchen to create her own doses of a popular weight-loss drug.

“I’m playing doctor,” Bookless said, describing her foray into the world of do-it-yourself GLP-1 medication, injections developed to control diabetes and now also used for weight loss.

Her journey began conventionally enough. She’d first heard of Wegovy, a GLP-1 made by Novo Nordisk, from a friend’s success story. Bookless then talked to her own doctor, who told her it wasn’t medically necessary and insurance wouldn’t pay for it because her body mass index wasn’t high enough to qualify her for coverage (without insurance, the cost can be $1,300 a month). So Bookless took matters into her own hands. And it led her to the fringes of a booming weight-loss drug market.

First, she considered her alternatives. She could go to a med-spa, but that would cost about $1,000 a month, still too much for the new therapist. Then, another friend at work told her about getting it directly from a laboratory that produces the product. Bookless wasn’t sure about this method — it meant having no doctor to turn to if she had questions — but a friend of hers assured her it was a legitimate, and a much cheaper route. She put her order in, paid $130, and two days later, in August, a package with a vial of white powder, sterile water, and needles arrived in the mail. It was semaglutide, a drug sold under the brand names Ozempic (for diabetes) and Wegovy (for weight loss).

Following instructions provided in the packaging, she mixed the powder and water and put it in the fridge, taking out one-fourth to one-half a milligram to inject herself in the stomach once a week.

Instead of consistently stepping up the dose to a target dose of 2.4 mg as the manufacturer’s instructions and FDA’s guidance recommend, she’s been sticking close to the amount she started with. Even at these lower-than-recommended levels, her appetite soon winnowed and she began to shed weight. Bookless has used two months’ worth of the semaglutide over three months of jabbing herself weekly.

Twenty-three pounds of weight loss later, she’s figuring out how low of a dose she can use.

“I don’t want to lose any more weight,” she said. “But I also don’t want to gain the weight back. It’s going to be an experiment to go off of it.”

As demand for popular weight-loss drugs like Wegovy and Zepbound skyrockets, Bookless’ DIY approach highlights the lengths some are willing to go to slim down while saving money. Some patients, with or without the help of doctors, are experimenting with “microdosing” weight loss drugs — using smaller-than-recommended amounts — in order to stretch limited supplies, reduce costs and even potentially curb side effects.

Meanwhile, medical experts are raising concerns, saying that there are not enough data about the effects of such weight loss drugs on those with lower BMIs and that the consequences of such off-label use remain largely unknown.

“We don’t have any clearly identified risks of people using it if they don’t meet criteria,” said Dr. Alyssa Dominguez, a specialist in endocrinology, diabetes and metabolism at the USC Keck School of Medicine. “But we don’t know because we haven’t been looking at those people in the scientific way.”

When the semaglutide medication Wegovy first hit the market in 2021, it became the first weight-loss drug to get FDA approval since 2014 and immediately became the go-to weight-loss treatment. At the heart of these medications are two key hormones, depending on the drug: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). These naturally occurring hormones play crucial roles in regulating insulin, appetite and metabolism.

At first, these medications were used to treat diabetes. But when the FDA finally gave pharmaceutical companies approval to use these same drugs for weight loss, demand for them skyrocketed.

The enthusiasm wasn’t just about dropping pounds. A landmark study in 2023 found that semaglutide reduced major cardiovascular events by 20%, even in patients without diabetes. Perhaps most striking was a 19% lower death rate from any cause. With more than 70% of American adults affected by obesity or overweight — conditions that increase risk for heart attack, stroke and premature death — these findings suggested that injecting oneself with Ozempic, or any number of the other brands semaglutide are sold under, could offer significant long-term health benefits.

The popularity led to sky-high prices, supply shortages and, in some cases, desperate measures by those seeking to lose weight.

No matter the drug, microdosing is an inexact art. The weight-loss drug users and doctors whom The Times spoke to for this story all had slightly different takes: staying closer to the starting dose of 0.25 milligrams, cutting down to as low as 0.1 milligrams or simply refraining from injecting the medication every seven days as recommended. While “microdosing Ozempic” joins the lexicon on gentler-sounding beauty terms like “baby Botox” and “mini face lift” that make procedures seem more approachable, the reality is that some people do see benefits from lower doses.

Even as this approach gains popularity, pharmaceutical companies advise patients against adjusting dosages.

“We do not condone these practices and it’s important to understand that for Ozempic, only the marked doses on the pens (0.25, 0.5, 1.0 and 2.0 mg) are approved for use (with 0.25 mg only approved for initiation and not maintenance),” a Novo Nordisk spokesperson said in an email. “The approved doses are the only dose strengths that have been studied as maintenance doses in our phase 3 clinical development program.”

“The products are not interchangeable and should not be used outside of their approved indications,” the spokesperson added.

Dr. Vijaya Surampudi, associate director of the UCLA Medical Weight Management Clinic, works with patients who want to stay at lower doses. She emphasizes that patient responses to these medications vary widely and the need for higher doses doesn’t necessarily correlate with how much weight someone needs to lose. Instead, she carefully monitors each person’s reaction to the medication, tailoring the approach based on their body’s unique response.

“No one size fits all,” she said.

But there are practical limitations in microdosing weight-loss medications, she said. Brand-name GLP-1 medications come in fixed-dose pen injectors, making personalized dose adjustments impossible.

Bookless found a way around this roadblock by acquiring a compounded version of the medication, a copy of brand-name medicines. Federal law normally bans pharmacies from making copycat versions of commercially available drugs. But when medications are in short supply, regulators don’t consider them “commercially available” — opening the door for pharmacies to create and sell similar products.

Dr. Tasneen Bhatia, better known as Dr. Taz, an integrative medicine physician and wellness expert, offers compounded GLP-1 to clients at her Los Angeles office, where she estimates about 10% to 20% of clients are microdosing the medication.

Bhatia sees microdosing as an option for clients who come to her office with the goal of losing 20 pounds or less or patients who have proved to be sensitive to the side effects of GLP-1, which include nausea, constipation, lack of energy and diarrhea.

Because early research shows many patients regain weight once they cease use of GLP-1, Bhatia says many doctors expect patients to use these medications for the rest of their lives. Bhatia, however, sees a future where people microdose the drug on and off as needed, something she acknowledges is not yet conventional wisdom.

“I think by switching it up, you’re challenging the metabolism a little bit, and so using it more, maybe once a quarter, to get back on track,” she said. “The goal should never be that someone has to be on something forever.”

Dr. Suzanne Trott, a Beverly Hills board-certified plastic surgeon, started a microdosing clinic after her patients had used the medication to reach their goal weight and hoped to maintain it. She works only with tirzepatide — the drug behind Zepbound that uses both GIP and GLP-1 — which, in her experience, has fewer side effects. She sources the drug from a compounding company that has facilities in Southern California. Trott said she works with her patients to figure out the amount and schedules injections as needed.

“They can try to microdose however they want it,” she said. “Not all of medicine is science; some of it is an art.”

The microdosing works so effectively that she said it’s cutting into the plastic surgery side of her business. She recommends it as a safer alternative to liposuction for some patients.

No matter how effective doctors and patients say microdosing weight-loss drugs are, this form of medical experimentation may be short-lived. Once shortages ease, companies peddling these alternatives could face a crackdown. Last week, the Food and Drug Administration announced that the shortage of Eli Lilly’s Zepbound was over, though Wegovy remains scarce. Eli Lilly then sent cease-and-desist letters to many companies offering compounded versions of tirzepatide.

Shortly after being sued by the Outsourcing Facilities Assn., a compounding trade group, the FDA reversed its decision and said it would allow pharmacists to continue making compounded versions of the drug while it reexamines the shortage.

Semaglutide compounders could be next: Novo Nordisk has asked the FDA to bar compounding pharmacies from making compounds of its weight loss and diabetes drugs, arguing the medication is too complex for it to be manufactured by others safely.

With the compounded versions still available (for now), Trott said her clinic is almost at capacity, with a couple dozen patients. She remains optimistic about the widespread appeal of these treatments.

“It’s something that’s become a part of a lot of regular people’s lives,” she said. “Kind of like the way plastic surgery used to be just something that celebrities did, and now this is something that is accessible to everyone.”