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Does phentermine help with ADHD?

Phentermine is sometimes prescribed off-label for the treatment of ADHD. Here’s what you should know.
Wendy Wisner
By | Jul. 20, 2024 Medically reviewed by Anne Jacobson, MD, MPH
Blue and white Rx capsules: Phentermine for ADHD

Key takeaways

  • Phentermine is a central nervous system stimulant medication that is approved by the FDA for short-term use to aid in weight loss.

  • Phentermine is not approved by the FDA to treat ADHD. It may sometimes be prescribed off-label for that purpose.

  • There are very few studies that look at the effectiveness of phentermine as an ADHD medication.

  • Possible side effects of phentermine include dry mouth and digestive issues like nausea, vomiting, diarrhea, and constipation.

In this article:

Phentermine is a central nervous system (CNS) stimulant approved by the U.S. Food and Drug Administration (FDA) as a weight loss medication. It is a Schedule IV controlled substance and is sold under the brand names Adipex-P and Lomaira. Phentermine is meant to be used on a short-term basis to assist in weight loss for people with obesity (BMI 30 or more) or for people who are overweight (BMI 27 or more) who also have risk factors such as controlled high blood pressure, diabetes, or high cholesterol. It’s recommended that phentermine be used with other lifestyle changes like exercise and a healthy diet.

Phentermine works by stimulating norepinephrine and epinephrine release and has a mechanism of action similar to amphetamines, which are often used to treat attention deficit hyperactivity disorder (ADHD). As such, people may wonder if it’s possible to use phentermine for ADHD. As of now, phentermine is not FDA-approved for ADHD, and the evidence of its effectiveness is scarce. However, healthcare professionals sometimes prescribe phentermine for off-label uses, such as for the treatment of ADHD.

Can phentermine be used to treat ADHD?

As to whether or not phentermine is effective in the treatment of ADHD, there are no robust clinical trials regarding the use of phentermine as an ADHD medication. 

Jenepher K. Piper, MSN, CRNP, a nurse practitioner at Mercy Medical Center in Baltimore, emphasizes that phentermine is not approved for this use. “Phentermine is an old psychotropic medication that is indicated by the FDA for the short-term treatment of weight loss,” she says. “It does not have the approved indication for ADHD.”

However, Piper says, phentermine is closely related to prescription medications that are approved for ADHD, including Dexedrine, which is approved by the FDA to treat ADHD and narcolepsy. Phentermine is also similar in action to Vyvanse, a medication that’s FDA-approved to treat ADHD and binge-eating disorder, though not weight loss specifically.

A 2016 article published in Frontiers in Pharmacology noted that phentermine has similarities with the CNS stimulant dexamphetamine, which is found in ADHD medications like Dexedrine, ProCentra, and Zenzedi. The study researchers also note that phentermine can improve executive functioning, which refers to the ability to plan ahead and exhibit self-control, both of which can be challenging for people with ADHD. 

How does phentermine work for ADHD?

The evidence regarding phentermine’s effectiveness for treating ADHD is scarce, Andrew Youssouf, MD, double board-certified in addiction medicine and emergency medicine and medical director of Ikon Recovery, explains. “This medication is not typically prescribed for managing ADHD symptoms,” Dr. Youssouf says. “Its main application is in weight loss, not addressing the challenges associated with ADHD.”

Still, phentermine shares attributes with other ADHD medications and has a similar mechanism of action in the body. “Phentermine stimulates the release of norepinephrine, which can influence alertness and appetite,” Dr. Youssouf says. Still, “its effects on ADHD symptoms are not well-documented,” he stresses.

According to Piper, phentermine may help increase focus and decrease ADHD symptoms in the following ways:

  • Increasing dopamine levels, which can improve alertness and focus via the brain’s pre-frontal cortex.
  • Increasing serotonin levels, which boosts mood and motivation.
  • Increasing norepinephrine, which heightens energy and ignites the “fight or flight” system in the body.

How long would it take phentermine to work? When it comes to appetite suppression, it usually takes about three to four hours. However, it’s not known how long it would take for phentermine to treat ADHD symptoms since this hasn’t been extensively studied.

There are also no guidelines for the correct phentermine dosage for ADHD because phentermine is not FDA-approved to treat ADHD. 

Potential side effects of phentermine 

Though many people tolerate phentermine well, it’s not without side effects. Potential common side effects include:

  • Unpleasant taste in the mouth
  • Dry mouth
  • Nausea
  • Vomiting
  • Constipation
  • Diarrhea

Sometimes, more serious side effects can occur, which may include:

  • Elevated blood pressure
  • Heart palpitations
  • Increased heart rate 
  • Feeling restless
  • Lightheadedness
  • Tremors
  • Trouble sleeping
  • Labored breathing
  • Chest pressure or pain
  • Swollen legs and ankles
  • Difficulty exerting yourself, such as in exercise

“Phentermine isn’t meant for long-term use, but when it is used this way, adverse reactions can sometimes occur especially addiction and cardiovascular concerns.” Dr. Youssouf states.

“Prolonged use could result in tolerance or reliance,” Dr. Youssouf warns. “It can also raise blood pressure and pulse, which may pose hazards for individuals with heart problems.”

Alternatives to phentermine for ADHD

There are certain people who should not use phentermine, Piper says. This includes “anyone with a heart condition or uncontrolled anxiety, eating disorder or mood disorder,” she explains.

According to DailyMed at the National Institutes of Health (NIH), the following medical conditions are contraindications to phentermine use:

  • Advanced arteriosclerosis (hardening of arteries)
  • History of heart disease
  • Moderate to severe high blood pressure (hypertension)
  • History of agitation
  • History of substance abuse
  • Hyperthyroidism
  • Glaucoma
  • People who have used monoamine oxidase inhibitors (MAOIs) within the past 14 days

Additionally, caution should be exercised for people in the following categories:

  • People with mild hypertension
  • People with diabetes who take insulin
  • People who take blood pressure medications, such as guanethidine

The following people also should not use phentermine:

  • Pregnant individuals
  • Breastfeeding parents
  • Children

Phentermine is not well studied in terms of ADHD treatment, nor is it safe for everyone who may be interested in taking it. But the good news is that there are many viable alternatives to phentermine for ADHD.

“As for alternatives, medications such as Ritalin (methylphenidate), Adderall (amphetamines), Strattera (atomoxetine), and Intuniv (guanfacine) have undergone thorough research and are considered safer and more effective options for treating ADHD,” says Dr. Youssouf.

Piper says that there are many better-targeted and tolerated meds for ADHD than phentermine. These include:

The best way to know if phentermine might work for you is to contact your prescribing healthcare provider. Make sure to talk to your healthcare provider about all of your medications, including supplements, to avoid possible drug interactions. “Seeking guidance from a healthcare professional is necessary to determine the most suitable treatment options tailored to one’s specific health needs and conditions,” Dr. Youssouf recommends.

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