How Does Taking Phentermine for Weight Loss Make You Feel? - GoodRx (2024)

Nearly 40% of Americans are labeled as obese. And it feels as if our nation is constantly searching for a magic bullet to keep weight off. Many people are now turning to injectable medications like Ozempic and Wegovy. But one of the first weight-loss medications on the market — phentermine — is still a popular choice.

Phentermine (Adipex-P, Lomaira) is known for boosting energy and suppressing appetite, helping with the two main components of weight loss: eating less and moving more. But the medication has known side effects, such as dry mouth and trouble sleeping.

In 2020, more than 3 million Americans were prescribed phentermine for weight loss. GoodRx talked to three people about their experiences with phentermine. Here’s what they had to say.

Phentermine helped a nurse take off baby weight

When Jasmine Addison’s daughter was born nearly 3 years ago, Jasmine’s weight climbed to its highest ever, almost 300 lbs.

The 23-year-old New York City resident looked to her own mother for weight-loss inspiration.

“She was over 400 lbs and really obese when I was younger,” Jasmine says. “Within the past 4 years, she’s lost more than 150 lbs.”

Jasmine decided to follow in her mother’s footsteps and try phentermine. She talked to her doctor and started taking 37.5 mg daily.

“It takes your appetite away,” Jasmine says. “I used to eat a lot. And then, you go on phentermine, and it kind of cuts your appetite in half.”

She adds, “When you are not as hungry, it allows you to make more conscious decisions on what you eat. When you're really hungry, it's hard to make a conscious decision. You're just going to choose whatever is available.”

Jasmine, a licensed practical nurse who is on her feet a lot, also likes the added pep phentermine brings to her life. “You do get a burst of energy,” she says. “It’s really hard to get up in the morning and work out, so I feel like it helps with that type of energy.”

Jasmine says phentermine also makes her sweat more when she is working out, helping her keep off water weight.

But it isn’t all positive. “The bad part is you get very jittery,” she says. “If you’re not on a good diet, you could possibly get really dizzy. And when you’re off it for a while, you get a weird withdrawal feeling and start sweating.”

Jasmine took phentermine for a year and a half in total. When she started taking it the first time, she lost 50 lbs in 3 months. Then, after taking a break and restarting treatment, she dropped to under 200 lbs. She took breaks from the medication because she had heard about possible side effects, such as heart palpitations. She worried about her risk of having a stroke and heart attack. But neither she nor her mother experienced any heart-related side effects.

“I just felt that, if you take it the proper way, you’ll be fine,” she says. “That’s just how I feel. Like, too much of everything is bad.”

Jasmine says she does experience insomnia while taking phentermine: “I feel like it plays a part in the endless nights of not being able to sleep.”

Still, she says, the positives outweigh the negatives.

“I would recommend it to anybody who has binge-eating problems or is super overweight and they’re feeling like they can’t lose that weight fast enough,” she says. “It’s a great jumpstart.”

Phentermine helped an Air Force recruiter lose 50 lbs

Childbirth — two kids in 3 years — also led to Ashley Kasper’s quest for weight loss. She first explored popular GLP-1 agonists, the class of medications that includes Ozempic and Wegovy. When she found them to be too costly with her prescription medication coverage, she talked to her doctor about alternatives.

Not long after, she started a 3-month course of phentermine. She combined the medication with eating nutritious meals and working out. And she noticed that the weight started coming off immediately. By Week 12, she had lost about 30 lbs. At Week 20, she was down a total of 53 lbs.

Ashley, a 27-year-old recruiter for the U.S. Air Force in Bozeman, Montana, says weight loss is more than an issue of vanity for her. Diabetes runs in her family. And she needs to be fit to achieve her military fitness requirements.

She says phentermine works exactly as advertised: It takes away her appetite. The first time she took the medication, she was planning on grabbing breakfast on the way to work. But the medication worked so quickly, she didn’t feel like eating.

“That’s how I knew it was working, because this is not normal for me,” she says. “Not even an hour in and it kicks in.”

Ashley grew up associating food with times when she was enjoying herself. But with phentermine taking away her hunger, she thinks more rationally about food now.

“I really struggle with a bit of a food addiction,” she says. “I love to cook. I love to bake. I love to go eat. So getting rid of all that food noise in my head just made it so easy to eat healthy. It doesn’t bother me mentally or physically.”

Ashley eats small snacks during the work day and a sensible dinner with her husband at night. She estimates that she eats about 1,200 calories a day, with the help of phentermine controlling her hunger. She watches her calorie intake because she has a sedentary job that requires a lot of driving and sitting, but not a lot of energy.

Ashley takes a 37.5 mg dose of phentermine daily. Before having children, she says, she’d always been skinny. After kids, her highest weight was 223 lbs.

The maximum weight for someone of Ashley’s height who is entering the Air Force is 191 lbs. And while the weight standards do not apply to those already in service, Ashley says she felt like a hypocrite telling potential recruits they’d need to lose weight when she was heavier than the maximum weight.

“I just felt like I wasn’t a good representation of a good military image,” she says.

Ashley experiences very few side effects from the medication. But she has experienced some insomnia, an extremely dry mouth, and bad body odor.

“I’ve talked to a few girlfriends about [the body odor issue], and it seems to be related to being in a huge calorie deficit,” she says.

She did feel her heart racing one time after she took phentermine. It was a couple of hours after she took the medication, just before she had to give a short public presentation

“My heart started pounding to the point I could hear it in my chest,” she says. “My heart has never pounded like that, and I wasn’t that nervous. It bothered me to the point where I was, like, ‘I’m not taking medication for the next few days.’”

She tracked her heart rate with her Apple Watch. And, eventually, she chalked it up to the combination of the medication and adrenalin from preparing for the presentation.

“I’m never going to pretend I’m the doctor, because I know some risks come with this. And that’s why not all doctors recommend it,” she says.

She plans to do another 3-month course of phentermine and then stop taking the medication permanently.

“They say it’s not a magic pill, but for me it has been a magic pill,” she says. “I feel like I’m one of the lucky ones.”

The side effects made a government contractor wary of continuing treatment

Key’Miya Pinkney is unsure about her future with phentermine. While it’s helped her lose weight, the unwelcome side effects — insomnia, anxiety, and heart palpitations — give her great pause about continuing to take it.

“I don’t know if I want to keep going with these problems. Because, in the end, will they have a bigger effect?” she says. “I feel like I’m going to come out with a heart problem because I wanted to lose weight from a pill.”

Her phentermine journey started in April 2023, when she posted online that she wanted help losing weight. The 21-year-old says her binge-eating disorder caused her to reach a top weight of 465 lbs.

Key’Miya heard about phentermine and asked her doctor about it. Her doctor prescribed her 37.5 mg daily.

“I was losing weight, and it decreased my appetite to the point where I would go without eating for a day, almost 2 days, without realizing it,” she says. “I was, like, ‘did I eat?’ because I wasn’t hungry.”

Phentermine also gave Key’Miya a lot of energy, so she joined a gym. But after becoming self-conscious about people looking at and judging her, she settled into a routine of walking in her neighborhood.

Key’Miya says that phentermine’s side effects give her pause.

“A lot of insomnia came with it. I would go 2 days without sleeping,” she says, adding that she also had really bad heart palpitations. “I had really bad chest pains, and my anxiety levels were up. It made me feel like I was going to have a heart attack.”

While she lost 36 lbs in 4 months, she’s torn about whether to continue taking phentermine. She says that she loves the weight loss, but at what cost?

“If it could cause real bad health problems in the long run, it’s not worth it,” she says. “You’re better off trying something else or trying to lose it the natural way.”

What does the pharmacist say?

Stacia Woodco*ck, PharmD

Pharmacy Editor

Phentermine (Adipex-P, Lomaira) is a medication that’s FDA approved for weight loss in combination with good nutrition and regular exercise. It’s available in several different forms you take by mouth: tablets, capsules, and orally disintegrating tablets. And it’s generally more affordable than the newer injectable weight-loss medications.

Phentermine is a stimulant medication. It helps lower your appetite, so you don’t feel as hungry and eat less while you’re taking it. Most people take 15 mg to 37.5 mg once daily in the morning. But it also comes in 8 mg tablets you can take 3 times a day before meals. Your provider will determine the best phentermine dosage for your needs, based on your other medications and health conditions.

Phentermine is only approved for short-term use, but some studies show that long-term use is likely safe. Still, you shouldn’t take phentermine for more than 12 weeks or so without a provider’s OK.

Phentermine’s stimulant effects can lead to side effects such as dry mouth, insomnia, and tremors. Constipation is also possible. These side effects will often improve as your body adjusts to the medication. But if they don’t, talk to your healthcare provider. They may want you to try a lower phentermine dosage.

The stimulating effects of phentermine can also cause your heart to beat faster than usual. So it’s not recommended if you have existing heart problems. But clinical studies have shown that there’s little long-term risk of heart issues related to taking phentermine if you don’t have underlying heart problems. In fact, the weight loss from taking phentermine leads to improved heart health overall.

It’s best to see your provider regularly while you’re taking phentermine, so they can make sure it isn’t causing any negative effects. And if you have trouble breathing, chest pain, or ankle swelling while you’re taking the medication, let your provider know right away. These could be signs of more serious heart-related side effects.