Drug & supplement interaction

Light Therapy + Phentermine, Topiramate

Phentermine, Topiramate brand name: Qsymia.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Light Therapy has a moderate interaction with Phentermine, Topiramate. Light therapy may increase the risk for photosensitization.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Light Therapy and Phentermine, Topiramate

Here is the interaction we found between these two, with the evidence behind it.

Moderate

PHOTOSENSITIZING DRUGS

Why this applies to Phentermine, Topiramate

Phentermine, Topiramate falls under PHOTOSENSITIZING DRUGS — the group Light Therapy interacts with.

Light therapy may increase the risk for photosensitization.
Concomitant use of photosensitizing drugs with light therapy may increase the risk for phototoxicity and should be avoided.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the basic idea with Qsymia (phentermine and topiramate) and light therapy. The concern isn't that one changes the blood level of the other. Instead, topiramate can sometimes make your skin and eyes a little more sensitive to bright light, so pairing it with concentrated light box exposure could, in theory, raise the chance of a phototoxic reaction like eye irritation or skin redness.

I'll be honest with you: this is a theoretical caution based on pharmacology, not something we see happen often. It doesn't make your weight-loss medicine work better or worse. Still, since light therapy shines bright light right at your eyes, it's worth a quick chat with your doctor or pharmacist before starting, especially if you notice any eye discomfort.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Pathirana, D., Ormerod, A. D., Saiag, P., Smith, C., Spuls, P. I., Nast, A., Barker, J., Bos, J. D., Burmester, G. R., Chimenti, S., Dubertret, L., Eberlein, B., Erdmann, R., Ferguson, J., Girolomoni, G., Gisondi, P., Giunta, A., Griffiths, C., Honigsmann
  2. Leon, A., Nguyen, A., Letsinger, J., and Koo, J. An attempt to formulate an evidence-based strategy in the management of moderate-to-severe psoriasis: a review of the efficacy and safety of biologics and prebiologic options. Expert Opin Pharmacother 2007; PubMed
  3. Morgan, M. and Khan, D. A. Therapeutic alternatives for chronic urticaria: an evidence-based review, Part 2. Ann Allergy Asthma Immunol 2008;100(6):517-526. PubMed
  4. Hoare, C., Li Wan, Po A., and Williams, H. Systematic review of treatments for atopic eczema. Health Technol Assess 2000;4(37):1-191. DOI
  5. Whitton, M. E., Pinart, M., Batchelor, J., Lushey, C., Leonardi-Bee, J., and Gonzalez, U. Interventions for vitiligo. Cochrane Database Syst Rev 2010;(1):CD003263. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Light Therapy Also Interacts With Other Medications

Light Therapy has 334 moderate known drug interactions in our database — the Phentermine, Topiramate one above is one of them. If you take anything else, check it against the full list below.

Moderate 334 No known interaction 2,496 (incl. Phentermine, Topiramate)
Taking anything else?

Check Another of Your Medications Against Light Therapy

Covers the 2,830 medications we’ve checked against Light Therapy. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Phentermine, Topiramate

This page covers Light Therapy only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Phentermine, Topiramate page lists 125 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), Activated Charcoal (major), Beer (major), Gamma-hydroxybutyrate (ghb) (major) and Kava (major).

By severity: 7 major · 101 moderate · 17 minor.

From our pharmacist’s overview on the Phentermine, Topiramate page

“Alcohol is the single biggest hazard on this page. Beer and wine both carry major-rated interactions with Qsymia (phentermine and topiramate), because topiramate already slows the nervous system and drinking deepens that sedation.”

Reviewed by 2 · Jul 18, 2026

Open the Phentermine, Topiramate interaction page

How much people look this up

Where Light Therapy and Phentermine, Topiramate Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Light Therapy
Steady interest

#883 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Phentermine, Topiramate
Top 25%

#423 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Treatment approach

About Light Therapy

What is Light Therapy?

  • Seasonal affective disorder (SAD)
  • Non-seasonal depression
  • Sleep and circadian rhythm problems
  • Jet lag and shift-work sleep issues
  • Certain skin conditions

Light therapy uses controlled exposure to bright artificial light and is best supported for seasonal affective disorder, where it is a recognized treatment option. It is generally safe for most people when used as directed, but you should talk to a doctor or pharmacist first, especially if you have eye conditions, bipolar disorder, or take medicines that increase light sensitivity.

Read the full Light Therapy monograph & all interactions
Keep checking

Other Drugs & Light Therapy

Browse every other medication we’ve checked against Light Therapy — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
334Moderate
0Minor
2,495No known interaction
334 Moderate 2,495 No interaction
Moderate

334 interactions

Showing 60 of 334 moderate interactions — see all 334 on the Light Therapy page.

No interaction 2,495 drugs checked — show the list

We also checked Light Therapy against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,495 medications checked with no known interaction — see the full Light Therapy list.

See the full Light Therapy interactions page
See every supplement checked against Phentermine, Topiramate, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Light Therapy monograph › Uses, safety, and every drug interaction in one place Phentermine, Topiramate supplement interactions › Every supplement checked against Phentermine, Topiramate, ranked by severity Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Having Light Therapy While Taking Phentermine, Topiramate: Common Questions

Can you have Light Therapy while taking Phentermine, Topiramate?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Light Therapy and Phentermine, Topiramate interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Phentermine, Topiramate and Light Therapy?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.