Long before Wegovy and Ozempic were filling the medicine cabinets of Hollywood elites, phentermine was the hottest name in weight loss. At one time this appetite suppressant accounted for three out of four weight-loss drug prescriptions (1). The reason for phentermine’s prescription pad popularity is that, when paired with diet and exercise, it can really rev up weight loss (2). It remains popular to this day for that reason; but no drug is perfect, and among other side effects like dry mouth and dizziness, some users have suggested phentermine causes hair loss (3).
Despite hair loss not being an officially recognized side effect, some users have reported feeling a little lighter up top while taking it. Is the potential risk of losing your locks worth abandoning a drug that could help you shed extra pounds and get healthier?
About the experts
Ross Kopelman, D.O., is a Hair Restoration Surgeon practicing at Kopelman Hair Restoration in New York City, New Jersey, and Palm Beach, FL.
Michele Green, M.D., is a board-certified Cosmetic Dermatologist practicing in New York City.
Does Phentermine Cause Hair Loss?
Research says no
Phentermine, which is sold under brand names like Adipex and Suprenza, belongs to a group of weight-loss meds called anorectics. It works by reducing appetite. When you aren’t hungry, you eat less. Makes sense. And it does work. People who take phentermine can lose 5 percent of their body weight on average (4).
But what about its effect on your hair? While some users have reported thinning, there’s no solid research linking phentermine directly to hair loss. “There are no clinical studies proving that this medication causes hair loss,” explains Ross Kopelman, D.O., a hair restoration specialist. “However, there are case reports and anecdotal evidence suggesting a potential link.”
But it might still cause some hair loss
A few studies have been done on some of phentermine’s chemical relatives, like amphetamine, which is prescribed for weight loss and attention-deficit hyperactivity disorder (ADHD). In one of those studies, almost 2 percent of participants reported hair loss as a side effect. And if you think a few extra hairs going down your drain isn’t a big deal, one woman lost almost all her body hair after taking dextroamphetamin (7).
Theoretically speaking, how might phentermine cause hair loss? When you skimp on food, you miss out on nutrients you need for healthy hair, like, iron, zinc, and vitamins A, C, and D (5). “The rapid weight loss and associated nutrient deficiency can lead to hair loss and thinning,” explains Michele Green, M.D., a board-certified cosmetic dermatologist practicing in New York City.
Losing a lot of weight in a short period of time can also put your body into a state of shock. Remember fight-or-flight from your high school biology class? It’s kind of like that. When your body is stressed out, “it can cause what’s called telogen effluvium, which is essentially hair shedding,” Kopelman says.
Telogen is the shedding phase of the hair cycle that happens after your hair stops growing. Normally, about 5 percent of your hairs are in the telogen phase at any one time. But when your body is stressed — whether it’s from childbirth, an illness, or quick weight loss—up to 70 percent of your hair follicles go into this phase (6). “This leads to increased shedding and thinning of the hair,” says Green. The shedding will eventually stop, but you can expect to find more hairs in your shower drain, and in your brush, for a good six to nine months.
Because your diet might be lighter while you’re on phentermine, eat more nutrient-dense foods to play catch-up. “Specifically, foods rich in zinc, iron, vitamin B, and vitamin D will help prevent hair loss,” says Green. “These nutrients play key roles in hair growth.” You’ll find them in foods like eggs, spinach, cashews, chickpeas, and whole grains.
If your diet just isn’t cutting it in the nutrient department, tack on a multivitamin or supplement. Just be wary of those hair growth supplements that are loaded with biotin. While biotin is a building block of hair—trust us, you’re getting enough already. “Basically no one has a biotin deficiency unless they have a genetic issue,” Kopelman says. That said there’s no harm in using a biotin shampoo if you want to give your thinning hair a little more oomph.
These lifestyle changes should be enough to stem the flow of lost hair, but if you’re losing so much that it’s noticeable, you can try meds. “Topical minoxidil, also known as Rogaine, can be used to prevent hair loss while on phentermine,” says Green. “This over-the-counter hair loss treatment can prompt hair follicles to convert to the anagen, or growth phase, and boost blood flow to the scalp.”
While hair loss isn’t well-documented with phentermine, a few other side effects are. This drug can cause dry mouth, a weird taste in your mouth, diarrhea, constipation, and vomiting (2).
Other more serious side effects that affect your heart are also worth noting. Though they’re relatively uncommon, it’s worth being on the lookout for a racing heart, dizziness, shaking, shortness of breath, chest pain, and swelling in your legs and ankles (2). Definitely report any of these side effects to your MD.
The Bottom Line
There’s no hard evidence that phentermine causes weight loss—only a few personal stories here and there. If you do notice a little thinning, it’s probably due to your diet and some added nutrients should help.
Taking any medicine requires weighing the risks vs. benefits, and in this case the benefits likely outweigh the risks. “Someone who wants to take these weight loss medications for medical reasons because maybe they have diabetes or obesity … I would say losing weight is more important than worrying about whether you’re going to lose your hair,” Kopelman says.
