Drug & supplement interaction

L-cysteine + Insulin Glargine

Insulin Glargine brand names: Basaglar, Lusduna, Semglee.

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

L-cysteine has a moderate interaction with Insulin Glargine. Theoretically, taking L-cysteine supplements with antidiabetes drugs might increase the risk of hypoglycemia.

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

L-cysteine and Insulin Glargine

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

Moderate

ANTIDIABETES DRUGS

Why this applies to Insulin Glargine

Insulin Glargine falls under ANTIDIABETES DRUGS — the group L-cysteine interacts with.

Theoretically, taking L-cysteine supplements with antidiabetes drugs might increase the risk of hypoglycemia.
Animal research suggests that L-cysteine can have hypoglycemic effects.
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: insulin glargine is your long-acting, background insulin that keeps blood sugar steady throughout the day. The concern with L-cysteine is that, at least in animal studies, this amino acid seemed to nudge blood sugar a little lower on its own. Stack that on top of an insulin that already lowers blood sugar, and in theory you could dip too low (hypoglycemia).

I want to be honest about how soft this evidence is, though. We're talking about lab and animal data, not solid human studies, so this is more a heads-up than a red alert. Still, since low blood sugar can cause shakiness, sweating, confusion, or worse, it's worth a quick chat with your pharmacist or doctor before adding L-cysteine, and keep an eye on your glucose readings if you do.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Lee S, Han KH, Nakamura Y, et al. Dietary L-cysteine improves the antioxidative potential and lipid metabolism in rats fed a normal diet. Biosci Biotechnol Biochem 2013;77(7):1430-4.

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

L-cysteine Also Interacts With Other Medications

L-cysteine has 85 moderate known drug interactions in our database — the Insulin Glargine one above is one of them. If you take anything else, check it against the full list below.

Moderate 85 No known interaction 2,745 (incl. Insulin Glargine)
Taking anything else?

Check Another of Your Medications Against L-cysteine

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

Everything else you take

See Every Supplement That Interacts With Insulin Glargine

This page covers L-cysteine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Insulin Glargine page lists 242 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Chelation Therapy Products (major), Siberian Cocklebur (major), Acai (moderate), African Wild Potato (moderate) and Agaricus Mushroom (moderate).

By severity: 2 major · 211 moderate · 29 minor.

Open the Insulin Glargine interaction page

One more smart check

Taking L-cysteine as Part of a Dietary Supplement Product? Check It for Interactions

We hold 1 real supplement products containing L-cysteine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides L-cysteine. Your product may carry other ingredients that interact with Insulin Glargine too, on top of L-cysteine — 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 L-cysteine and Insulin Glargine 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 L-cysteine
Top half

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

29 days ago today
Medication Insulin Glargine
Top half

#960 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 L-cysteine

What is L-cysteine?

  • Antioxidant support
  • Skin and hair health
  • Liver support
  • Respiratory and mucus thinning
  • General protein/amino acid supplementation

L-cysteine is a sulfur-containing amino acid your body uses to make proteins and the antioxidant glutathione. Most people get enough from food, and supplements are usually well tolerated, but strong evidence supporting specific health benefits from extra L-cysteine is limited. Talk to your pharmacist or doctor before starting it, especially if you are pregnant, breastfeeding, or have a health condition.

Read the full L-cysteine monograph & all interactions
Medication

About Insulin Glargine (rDNA origin) Injection

What Is Insulin Glargine (rDNA origin) Injection Used For?

Brand names: Basaglar, Lusduna, Semglee

Insulin glargine is used to improve blood sugar (glucose) control in adults and pediatric patients with type 1 diabetes mellitus, and in adults with type 2 diabetes mellitus. It is a long-acting insulin that works around the clock to help keep blood sugar levels stable.

Insulin glargine is not recommended for treating diabetic ketoacidosis (a dangerous complication where the blood becomes acidic due to very high blood sugar).

See full Insulin Glargine (rDNA origin) Injection drug information
Keep checking

Other Drugs & L-cysteine

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

0Major
85Moderate
0Minor
2,744No known interaction
85 Moderate 2,744 No interaction
Moderate

85 interactions

Showing 60 of 85 moderate interactions — see all 85 on the L-cysteine page.

No interaction 2,744 drugs checked — show the list

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

Showing the 60 most looked-up of 2,744 medications checked with no known interaction — see the full L-cysteine list.

See the full L-cysteine interactions page
See every supplement checked against Insulin Glargine, 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
L-cysteine monograph › Uses, safety, and every drug interaction in one place Insulin Glargine supplement interactions › Every supplement checked against Insulin Glargine, ranked by severity Insulin Glargine (rDNA origin) Injection 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 L-cysteine and Insulin Glargine Together: Common Questions

Can you take L-cysteine with Insulin Glargine?
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 L-cysteine and Insulin Glargine 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 Insulin Glargine and L-cysteine?

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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.