Is It Safe To Take Phentermine And Adderall Together?

In our latest question and answer, the pharmacist discusses the dangers of taking Adderall with phentermine.


I'm starting on phentermine 37.5mg tabs for weight loss. I have an important exam the last week in June in which my doctor prescribed me Adderall XR 40mg to help me focus. How soon should I stop the phentermine to take the Adderall? The Adderall is only for testing purposes. I used it while in college but I've been off for a year.

Asked by Cece On May 15, 2019

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On May 15, 2019
Blue Adderall Pills Out Of Bottle with text - adderall with phentermine


Adderall (amphetamine salts) generally should not be taken with phentermine.

They both are considered 'sympathomimetic' (i.e. stimulant) drugs and have a very similar mechanism of action.

Taking them together can increase the risk of serious side effects, including:[1]

  • Increased blood pressure
  • Serotonin syndrome
  • Tremors
  • Nausea
  • Vomiting
  • Headache
  • Restlessness
  • Palpitations
  • Loss of coordination
  • Dizziness

Adderall and phentermine are so similar that using both together would be considered to be a duplication of therapy (which is why there is an increased risk of side effects).

It is important to discuss all the medications you have been prescribed with your doctor. It is unlikely that they would prescribe Adderall and phentermine to be used together, but if they did, they generally would give you specific instructions on how to use both safely.

How They Work

Adderall and phentermine are both psychostimulants, which work by increasing the release of various neurotransmitters in the brain, including:

  • Serotonin
  • Norepinephrine
  • Dopamine

This neurotransmitter release has a variety of noticeable effects, including:[2]

  • Decreased fatigue
  • Increase mental alertness
  • Increased motor activity
  • Improved mood
  • Suppression of appetite

As mentioned, Adderall and phentermine are very similar in how they work, but Adderall, overall, is considered to be more potent in regard to how it affects neurotransmitter release.

Dangers Of Combined Use

Phentermine and Adderall share a similar side effect profile. Taking both together increases the risk of these side effects occurring.

Perhaps the most concerning adverse effects if you are taking these together are:

  • Increases in blood pressure (and the associated increase in cardiovascular risk)
  • Serotonin syndrome
  • Overstimulation

Blood Pressure

Phentermine and Adderall both increase blood pressure and can increase the risk of cardiovascular events, like heart attack and stroke.

The prescribing information for Adderall XR states that, in general, stimulant medications can increase heart rate and cause an average increase in blood pressure of about 2 to 4 mmHg:

Stimulant medications cause a modest increase in average blood pressure (about 2-4 mmHg) and average heart rate (about 3-6 bpm), and individuals may have larger increases.

Combining stimulates likely increases the risk of these effects even more.

If you already have high blood pressure or pre-existing heart conditions, combining stimulants could be especially dangerous.[3]

Serotonin Syndrome

Serotonin syndrome is a rare but serious disorder that results from excess serotonin in the brain. If it occurs, immediate medical attention is required.

It isn't overly common, but the risk is greatly increased if you are taking more than one drug that has serotonergic effects

The symptoms of serotonin syndrome include:[4]

  • Hyperthermia (increased body temperature)
  • Hypertension (increased blood pressure)
  • Muscle spasms
  • Muscle rigidity
  • Mental status changes (e.g., agitation, delirium, hallucinations, coma)

The prescribing information for both phentermine and Adderall warn about serotonin syndrome and recommend not to combine them with other serotonergic agents.


Since Adderall and phentermine are both stimulants, there is a risk of overstimulation with combined use. This may manifest as:[5]

  • Restlessness
  • Tremors
  • Headache
  • Nausea
  • Insomnia
  • Twitchiness
  • Dizziness

If any of the above side effects occur, even with a single drug (i.e. either Adderall or phentermine), it is generally recommended to reduce your dose.

How Long Does Phentermine Last?

You mentioned in your question that you wanted to know how long before taking Adderall you should stop taking phentermine to avoid an interaction.

It's difficult to give a precise answer due to individual variability in metabolism of phentermine, but in general, the effects of the drug last between 12 and 14 hours (for doses of 30 and 37.5 mg).[6]

However, if you want to avoid phentermine being in your system entirely, you will need to wait much longer.

The reported half-life of phentermine is 19-24 hours. It generally takes around 5 to 6 half-lives for a drug to be considered completely eliminated from the body. Therefore, it would take around 5-6 days for it to no longer be present in your system.[7]


Adderall and phentermine are both psychostimulant medications. They are generally not used together due to the increased risk of side effects such as increased blood pressure and overstimulation.

  1. ^ Elsevier ClinicalKey Drug Interaction Checker. ClinicalKey
  2. ^ Amphetamine, past and present – a pharmacological and clinical perspective. PubMed
  3. ^ Amphetamine Toxicity. PubMed
  4. ^ Recognition and treatment of serotonin syndrome. PubMed
  5. ^ Potential Adverse Effects of Amphetamine Treatment on Brain and Behavior: A Review. PubMed
  6. ^ Phentermine Prescribing Information. AccessFDA
  7. ^ The ABCD of clinical pharmacokinetics. PubMed

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Office: 716-389-3076

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