Drug & supplement interaction

L-cysteine + Ulipristal Acetate

Ulipristal Acetate brand name: Ella.

No Known Interaction
Medically reviewed by · Updated June 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between L-cysteine and Ulipristal Acetate in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first.

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Interaction report

L-cysteine and Ulipristal Acetate

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Ulipristal Acetate and L-cysteine in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

L-cysteine safety at a glance

L-cysteine overall Use caution Generally well tolerated in food amounts, but the safety of high-dose supplements over time is not well studied.
Pregnancy Likely Safe When used orally in amounts found in foods. There is insufficient reliable information available about the safety of amounts greater than those found in foods;... Read the full pregnancy detail
Breastfeeding Likely Safe When used orally in amounts found in foods. There is insufficient reliable information available about the safety of amounts greater than those found in foods;... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Ulipristal Acetate and L-cysteine? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Ulipristal Acetate

Interactions in our licensed database are recorded against drug classes, not just single drug names. Ulipristal Acetate is filed under 3 classifications — contraceptive drugs, cytochrome p450 3a4 (cyp3a4) substrates, oral drugs. L-cysteine has documented interactions with 1 drug class — the most serious being antidiabetes drugs (moderate) — and none of Ulipristal Acetate’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

L-cysteine Does Interact With Other Medications

L-cysteine has 86 moderate known drug interactions in our database — Ulipristal Acetate isn’t one of them. If you take anything else, check it against the full list below.

Moderate 86 No known interaction 2,744 (incl. Ulipristal Acetate)
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.

What to actually watch for

What Ulipristal Acetate’s Own FDA Label Lists

This is not an interaction — none of it involves L-cysteine. These are the most notable effects listed in the ADVERSE REACTIONS section of Ulipristal Acetate’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both. 3 of them are worth acting on rather than waiting out — marked below.

  • A severe allergic reaction Worth acting on
  • Hives Worth acting on
  • An allergic reaction Worth acting on
  • Acne
  • Stomach pain mentioned in 5.6% of FDA reports for Ulipristal Acetate
  • Tiredness
  • Dizziness
  • Nausea mentioned in 7.8% of FDA reports for Ulipristal Acetate
  • Headache mentioned in 5.4% of FDA reports for Ulipristal Acetate
  • A skin rash

From the ADVERSE REACTIONS section of the FDA label for Ulipristal Acetate. Read the label on DailyMed › Where a percentage is shown, it is the share of 498 voluntary FDA FAERS reports for Ulipristal Acetate that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. L-cysteine’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no L-cysteine side to compare — that is a limit of the record, not a statement that L-cysteine has no side effects.

Special populations

L-cysteine in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Safe

When used orally in amounts found in foods. There is insufficient reliable information available about the safety of amounts greater than those found in foods; avoid use. Some research suggests that taking L-cysteine during lactation increases levels of free L-cysteine in breastmilk. However, these levels are lower than those found in some commercial hydrolyzed protein infant formulas.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

Everything else you take

See Every Supplement That Interacts With Ulipristal Acetate

This page covers L-cysteine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Ulipristal Acetate page lists 158 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), Acacia Rigidula (moderate) and Adrafinil (moderate).

By severity: 3 major · 107 moderate · 48 minor.

From our pharmacist’s overview on the Ulipristal Acetate page

“St. John's wort worries me most with ulipristal acetate (Ella), the emergency contraceptive that gets exactly one chance to work.”

Reviewed by 2 · Jul 18, 2026

Open the Ulipristal Acetate 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. Even though L-cysteine itself has no known interaction with Ulipristal Acetate, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where L-cysteine and Ulipristal Acetate 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
Steady interest

#1,184 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Ulipristal Acetate
Steady interest

#1,665 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every L-cysteine reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The L-cysteine and Ulipristal Acetate records this page draws on were last updated June 22, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
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.

Amino acid (not a plant part) · Capsules, tablets, powder; also available as N-acetylcysteine (NAC)

An interaction check asks whether these two react with each other — it does not ask whether L-cysteine is a good idea for someone in your situation. Here is what our L-cysteine record says about it on its own.

L-cysteine: dosing

There is no official standardized dose of L-cysteine established for general supplement use. Products vary widely in strength, and much of the dosing research actually involves NAC rather than plain L-cysteine.The safest approach is to follow the directions on the product label and not exceed the recommended amount. Higher doses have not been well studied and may increase the risk of side effects.

From our L-cysteine monograph — the full record covers uses, side effects and every documented interaction.

Read the full L-cysteine monograph & all interactions
Medication

About Ulipristal

What Is Ulipristal Used For?

Brand name: Ella

Ella (ulipristal acetate) is used to prevent pregnancy after unprotected sex or when another form of birth control has failed or was used incorrectly. It must be taken as soon as possible, within 5 days (120 hours) of that event.

Ella is intended for occasional, emergency use only — it is not a substitute for regular, ongoing contraception.

See full Ulipristal 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
86Moderate
0Minor
2,743No known interaction
86 Moderate 2,743 No interaction
Moderate

86 interactions

Showing 60 of 86 moderate interactions — see all 86 on the L-cysteine page.

No interaction 2,743 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 2,743 medications checked with no known interaction — see the full L-cysteine list.

See the full L-cysteine interactions page
See every supplement checked against Ulipristal Acetate, ranked by severity
Evidence & sources

L-cysteine References

The 2 references that drive our L-cysteine monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Dowlati Y, Maheux M, Meyer JH. The effect of oral L-cysteine on breast milk and plasma cysteine concentrations. Neuropsychiatr Dis Treat 2020;16:3163-3172.
  2. 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.

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking L-cysteine and Ulipristal Acetate Together: Common Questions

Is it safe to take L-cysteine with Ulipristal Acetate?
We do not list a known interaction between L-cysteine and Ulipristal Acetate. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
How was the L-cysteine and Ulipristal Acetate combination checked?
Interactions in our licensed database are recorded against drug classes. Ulipristal Acetate is filed under 3 classifications, and L-cysteine has documented interactions with 1 drug class — none of Ulipristal Acetate's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does L-cysteine interact with any other medications?
Yes. L-cysteine has 86 documented drug interactions in our database — Ulipristal Acetate is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Ulipristal Acetate interact with any supplements?
Yes. Ulipristal Acetate has documented interactions with 158 supplements in our database — L-cysteine is not one of them. The Ulipristal Acetate interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

L-cysteine monograph Uses, safety profile, and every drug interaction in one place Ulipristal drug information The full plain-English guide to this medication Ulipristal Acetate supplement interactions Every supplement checked against Ulipristal Acetate, 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 References The 2 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Ulipristal Acetate 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.