Drug & supplement interaction

Phenylalanine + Lioresal

Lioresal brand name: Lioresal Injection.

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

Phenylalanine has a moderate interaction with Lioresal. Concomitant intake of phenylalanine may reduce the intestinal absorption of baclofen.

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

Phenylalanine and Lioresal

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

Moderate

BACLOFEN

Why this applies to Lioresal

Lioresal falls under BACLOFEN — the group Phenylalanine interacts with.

Concomitant intake of phenylalanine may reduce the intestinal absorption of baclofen.
Phenylalanine and baclofen share the same intestinal carrier for absorption; phenylalanine competitively inhibits the absorption of baclofen, reducing its plasma levels.
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 gist for Lioresal (baclofen) and phenylalanine. Your gut uses a shared 'doorway' (a transporter) to soak up both of these from your intestines. When you take a phenylalanine supplement, it can crowd out baclofen at that doorway, so a little less baclofen gets into your bloodstream. In plain terms, your baclofen could end up working a bit weaker, which might mean more muscle stiffness, tightness, or spasms creeping back.

The good news: this is based mostly on lab-type research, not solid human studies, so it's a possible concern rather than a sure thing. Everyday amounts of protein in food aren't the issue here, it's concentrated supplement doses. If you take both, just check with your pharmacist or doctor before changing anything.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Cejudo-Ferragud, E., Nacher, A., Polache, A., Cercos-Fortea, T., Merino, M., and Casabo, V. G. Evidence of competitive inhibition for the intestinal absorption of baclofen by phenylalanine. Int J of Pharm (Amsterdam) 1996;132:63-69. DOI

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

Phenylalanine Also Interacts With Other Medications

Phenylalanine has 5 major, 10 moderate known drug interactions in our database — the Lioresal one above is one of them. If you take anything else, check it against the full list below.

Major 5 Moderate 10 No known interaction 2,815 (incl. Lioresal)
Taking anything else?

Check Another of Your Medications Against Phenylalanine

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

From our Q&A

Questions About Phenylalanine or Lioresal

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Phenylalanine or Lioresal, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Lioresal

This page covers Phenylalanine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Lioresal page lists 10 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Procaine (major), Biofeedback (moderate), Dendrobium (moderate), Ginkgo (moderate) and Lithium (moderate).

By severity: 1 major · 9 moderate.

From our pharmacist’s overview on the Lioresal page

“Lioresal is baclofen, a muscle relaxant prescribed for spasticity, and I would treat its supplement list with genuine care. Of the ten ingredients on file, six, including everyday picks like melatonin and ginkgo, may lower the seizure threshold, an added worry with a drug whose abrupt changes can already provoke seizures.”

Reviewed by 2 · Jul 18, 2026

Open the Lioresal interaction page

One more smart check

Taking Phenylalanine as Part of a Dietary Supplement Product? Check It for Interactions

We hold 1,990 real supplement products containing Phenylalanine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Phenylalanine. Your product may carry other ingredients that interact with Lioresal too, on top of Phenylalanine — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Phenylalanine and Lioresal 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 Phenylalanine
Top 10%

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

29 days ago today
Medication Lioresal
Steady interest

#2,776 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.

Supplement

About Phenylalanine

What is Phenylalanine?

  • Depression and mood
  • Skin condition vitiligo
  • Pain conditions
  • Attention and focus
  • Appetite control

Phenylalanine is an essential amino acid the body uses to make brain chemicals like dopamine and norepinephrine. Some people take it for mood, vitiligo, or pain, but the evidence is mostly limited or mixed. People with the genetic condition PKU must strictly avoid it.

Read the full Phenylalanine monograph & all interactions
Medication

About Baclofen

What Is Baclofen Used For?

Brand name: Lioresal Injection

Baclofen treats spasticity — the stiffness, muscle spasms, and rigidity that can come from neurological conditions. Oral forms (tablets, solutions, suspension, and granules) are used for spasticity from multiple sclerosis and spinal cord injuries or diseases. They are not intended for muscle spasm caused by rheumatic conditions like arthritis.

Intrathecal baclofen — delivered directly into the fluid around the spinal cord through an implanted pump — is reserved for severe spasticity that hasn't responded to oral baclofen, or when oral doses cause intolerable side effects. Gablofen (intrathecal injection) is specifically indicated for adults and children age 4 and older with spasticity of spinal or cerebral origin.

See full Baclofen drug information
Keep checking

Other Drugs & Phenylalanine

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

5Major
10Moderate
0Minor
2,814No known interaction
5 Major 10 Moderate 2,814 No interaction
Major

5 interactions

Moderate

10 interactions

No interaction 2,814 drugs checked — show the list

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

Showing the 60 most looked-up of 2,814 medications checked with no known interaction — see the full Phenylalanine list.

See the full Phenylalanine interactions page
See every supplement checked against Lioresal, 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
Phenylalanine monograph › Uses, safety, and every drug interaction in one place Lioresal supplement interactions › Every supplement checked against Lioresal, ranked by severity Baclofen drug information › The full plain-English guide to this medication 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

Taking Phenylalanine and Lioresal Together: Common Questions

Can you take Phenylalanine with Lioresal?
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 Phenylalanine and Lioresal 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 Lioresal and Phenylalanine?

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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.