Lomaira With Pristiq - Interaction Details

In our latest question and answer, the pharmacist discusses whether or not Lomaira can safely be taken with Pristiq.

2 min read Updated Jun 2026 318 views
Lomaira With Pristiq - Interaction Details
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Jill asked

Can you safely take Lomaira and Pristiq (50mg) together?

Oct 21, 2022
The quick answer
  • Taking Lomaira with Pristiq increases the risk of serotonin syndrome, a rare but serious condition with symptoms like muscle tremors, sweating, confusion, and increased heart rate.
  • Studies show this combination can be used safely together when the Pristiq dose is stable and you monitor for serotonin syndrome symptoms.
  • Contact your doctor immediately if you experience signs of serotonin syndrome while taking both medications.
A quick summary of Dr. Brian Staiger, PharmD's full answer below, condensed by AI from that answer only (not from any outside source). The pharmacist's answer is the source of record.
Medications in this answer — tap to explore

Answer

There is an interaction between Lomaira (phentermine) and Pristiq (desvenlafaxine) in that the combination increases the risk of a rare, but serious condition, known as serotonin syndrome, which can occur when taking multiple serotonergic drugs (i.e., drugs that affect the neurotransmitter serotonin).

However, this risk appears to be low and studies have shown that individuals taking both to treat obesity and concurrent depression can do safely as long as they monitor for side effects.

Interactions Details

Both Lomaira, which contains the active ingredient phentermine, and Pristiq (desvenlafaxine) can increase serotonin concentrations in the brain. Although rare, this increases the risk of serotonin syndrome, a condition characterized by:

  • Muscle tremors
  • Sweating
  • Increased body temperature
  • Confusion
  • Delirium
  • Increased blood pressure
  • Increased heart rate

It should be noted that this interaction is considered a relatively low risk of occurring, but it is nevertheless a possibility as phentermine is related to amphetamines, which have in rare cases, been determined to be contributing agents to individuals experiencing serotonin syndrome when used with other serotonergic drugs.

Having said this, phentermine's effect on serotonin is thought to be minimal at the usual recommended doses.

Additionally, there have been some large controlled clinical studies that have included individuals on both phentermine-based therapy for obesity along with their antidepressant (such as Pristiq), as long as the antidepressant dose had been stable for at least 3 months prior.

These studies have shown that such therapies were generally well-tolerated, especially at lower phentermine doses (which Lomaira would be at the recommended dosages).

What To Monitor For

Since studies have shown phentermine-based drugs (like Lomaira) have been used safely with drugs like Pristiq, they are sometimes prescribed together.

There are many drugs that increase serotonin concentrations in the brain and there will always be a theoretical interaction when 2 more of these drugs are used together (like Lomaira and Pristiq).

 It is just important to be aware of the symptoms of serotonin syndrome (as written above) and seek medical attention if they occur.

Final Words

Thanks so much for reaching out to us!

I hope this answer helped!

References & sources
  1. A toxic reaction from combining fluoxetine and phentermine — PubMed
  2. Amphetamine analogs increase plasma serotonin: implications for cardiac and pulmonary disease — PubMed
  3. Effects of low-dose, controlled-release, phentermine plus topiramate combination on weight and associated comorbidities in overweight and obese adults (CONQUER): a randomised, placebo-controlled, phase 3 trial — PubMed
  4. Controlled-release phentermine/topiramate in severely obese adults: a randomized controlled trial (EQUIP) — PubMed
  5. Lomaira Prescribing Information — Lomaira.com
Glossary — Terms in This Answer
Phentermine
A stimulant medication used to reduce appetite and help with weight loss.
Desvenlafaxine
An antidepressant medication that works by affecting certain chemicals in the brain.
Serotonin syndrome
A rare but serious condition that occurs when too much serotonin builds up in the body, usually from taking multiple medications that affect serotonin.
Serotonergic drugs
Medications that increase or affect serotonin, a chemical messenger in the brain.
Neurotransmitter
A chemical messenger in the brain that helps transmit signals between nerve cells.
Amphetamines
A class of stimulant drugs that increase energy and alertness.
Antidepressant
A medication prescribed to treat depression by altering brain chemistry.
Delirium
A temporary state of severe confusion and disorientation.
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Dr. Brian Staiger, PharmD
About the pharmacist

Dr. Brian Staiger, PharmD

Clinical Pharmacy

Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified

Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...

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