November 23, 2022

Can Phentermine Help with ADHD? | Scientific Evidence and Studies

by Bryan Wellington

Attention-deficit hyper-activity disorder (ADHD) affects millions of Americans every year. The most common drugs prescribed for ADHD are stimulants that send signals to the brain to produce more or less of certain compounds.

Some people don’t like the side effects of these stimulants, and look for alternative treatments, even treatments that are generally prescribed for other reasons. In this article, I’ll break down the reasons for taking alternative prescriptions, and why phentermine has entered the discussion for treatment of ADHD.

Key Takeaways

✲ “Off-Label” prescriptions are common; if a doctor recommends an off-label drug, it is not, in and of itself, a red flag.

✲ Phentermine has been seen in some studies to provide relief for ADHD symptoms.

✲ Another possible benefit of phentermine use is its ability to block norepinephrine, which may alleviate ADHD.

✲ Phentermine, despite its many uses, remains a Class IV drug, and comes with other side effects; phentermine requires a prescription.

Off-Label Prescriptions

Many medications are prescribed by physicians for uses not approved by the FDA. Commonly, when clinical trials test a medication, they only test for one variable. Does Drug X perform Y function? But in their tests, they may find a drug has secondary effects.

This is seen commonly in drugs like Topiramate, which was designed as an anti-seizure drug, but can also help with addictions and weight loss. The practice is called “off label” prescriptions.

If this sounds like malpractice or an illegal act, it is not. In fact, it is quite common. As long as the doctor prescribing the medication is clear with the patient what the medication is, what is approved for, what it does, and what the side effects could be, it is up to the patient to go forward with the prescription.

Phentermine as an Off-Label Prescription

Use of weight-loss drugs for other disorders, illnesses, or behaviors is a well-researched concept. In fact, many studies such as one found here go into great depth explaining the biochemical and hormonal benefits of established drugs in possible new uses.

There is strong anecdotal evidence that physicians are already prescribing phentermine for ADHD. But just because it is happening doesn’t mean there is good science to back up the reasoning.

Why Phentermine is Being Prescribed

A research paper published in the Primary Care Companion, which has a focus on Central Nervous System disorders (which ADHD falls into), highlighted several new therapies for treating ADHD that don’t involve straight stimulant drugs. One such therapy keyed in on norepinephrine and its transportation in the brain.

The Journal of the American Medical Association had a similar clinical trial. The furthest efficacy of norepinephrine treatment for ADHD is not yet explored, but data from both of these sources suggest this could be a safe treatment alternative.

Which brings us to phentermine. Several clinical trials which have evaluated the mechanisms of phentermine have concluded–using tools like blood sampling or brain imaging–that phentermine helps increase and regulate hormones like dopamine, serotonin, and yes, norepinephrine.

This link between hormones and ADHD is still tenuous, but the link between hormones and phentermine is well-established. That means that if there is any indication that hormones like norepinephrine are playing a role in a person’s ADHD, then phentermine, if safe for that given patient, may be an alternative choice of off-label medication.

How Doctors Get their Data

One might well ask, “If there’s no clinical trials proving phentermine for ADHD, then why are doctors prescribing it?” The answer is that doctors have available to them datasets which the public cannot see. These include patient records, and amalgamated data of patient records.

One facet of this is explored in my articles regarding side effects. Doctors are able to look through data which compiles key-words from anonymous patient records. For instance, they can search for a medication (like “phentermine”) and within the results look for a particular side effect (like “hair loss”, or "depression").

From that, even though they don’t have clinical trial data about that side effect, they can warn a patient that this is a risk.

That’s the same mechanism at work, here. If a patient wants to explore other options for their ADHD medication, their doctor can review database instances of other drugs, and index if patients also saw a decrease in ADHD symptoms. 

Because doctors have seen other patients safely use phentermine for ADHD, they may feel more comfortable prescribing it again


This has been a lengthy article, covering a lot of ground. But the information is important for anyone who wants to know how a doctor may be getting from point-A to point-B; especially in the realm of prescribing a weight loss drug for ADHD. In this case, the science seems to support a doctor’s and patient’s decision to go forward with this treatment route, provided it is safe for the patient. 

In all cases, decisions about medication should be made in consultation with a primary care physician who knows the patient and their history. Under no circumstances should a medication like phentermine be pursued without a doctor’s prescription.


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