Immune & defense Cyclic peptide immunosuppressant
Cyclosporine
Regulatory status
Status at a glance
503A compounding status
Not nominated
We found no pending nomination for the 503A bulks list. Unless the substance has another legal pathway (for example, a USP monograph or use in an FDA-approved drug), 503A pharmacies generally may not compound with it.
- FDA approval
- An FDA-approved product contains this peptide
- 503B outsourcing
- Not determined
- Anti-doping (WADA)
- Not on the WADA Prohibited List
- DEA schedule
- Not a controlled substance
About peptide status
Most peptides discussed here are not FDA-approved for any use, and products labeled “research use only” are not for human use. Removal from Category 2 does not authorize compounding. PCAC votes are non-binding recommendations; FDA and HHS make the final decisions.
This is not medical or legal advice, and we do not publish dosing, sourcing or reconstitution information. Talk with a licensed clinician before using any peptide.
If you think you are having a medical emergency, call 911.
Key takeaway
Cyclosporine (also spelled ciclosporin; brands include Sandimmune, Neoral, and the eye drop Restasis) is a cyclic peptide from a fungus that suppresses the immune system, and it transformed organ transplantation when it arrived in the 1980s. It works by blocking the activation of T cells. It has been FDA-approved in the U.S. since 1983, is available in oral, intravenous, and eye-drop forms, and carries boxed warnings for the systemic versions.
At a glance
- What it is
- A calcineurin-inhibitor immunosuppressant, a cyclic 11-amino-acid peptide of fungal origin
- Approved for
- Prevention of transplant rejection, severe rheumatoid arthritis, severe psoriasis, and (as Restasis) chronic dry eye
- Key fact
- In a landmark transplant trial it substantially improved one-year kidney graft survival over the prior standard
- Route
- Oral, intravenous, or ophthalmic
- Evidence strength
- FDA approved
Summary
Cyclosporine is a cyclic peptide that suppresses T cells. Learn how it works, its FDA-approved forms, and why systemic versions carry boxed warnings.
What is cyclosporine?
Cyclosporine, also spelled ciclosporin and known as cyclosporin A, is an immunosuppressant drug derived from a soil fungus. Chemically it is an unusual cyclic peptide, a ring of 11 amino acids including some that do not appear in ordinary proteins, which makes it fat-soluble and distinct from typical linear peptides. It is sold as Sandimmune, the microemulsion Neoral, and Gengraf for systemic use, and as the Restasis emulsion for the eyes. It was approved in the United States in 1983.
The history of cyclosporine
Cyclosporine changed the course of modern medicine. It was isolated from a fungus in the 1970s and found to suppress the immune system in a highly selective way, acting on the T cells that drive transplant rejection without broadly wiping out the bone marrow. Its approval in 1983 dramatically improved the survival of transplanted organs and helped make heart, liver, and other transplants routine rather than experimental. It remains a reference point for the calcineurin-inhibitor class.
How does cyclosporine work?
Cyclosporine enters T cells and binds a protein called cyclophilin, and the resulting complex blocks an enzyme called calcineurin. Calcineurin normally activates a transcription factor (NFAT) that switches on the gene for interleukin-2 and other signals T cells need to multiply and mount an immune response. By inhibiting calcineurin, cyclosporine prevents that activation, so the immune attack on a transplanted organ, or the overactive immune response in autoimmune disease, is suppressed.
That targeted suppression of T-cell activation is what made it so valuable in transplantation. In the landmark Canadian multicenter trial, cyclosporine improved one-year kidney graft survival compared with the older azathioprine-based regimen. The same mechanism underlies its use in autoimmune conditions and, at low local doses in Restasis, in reducing the inflammation of chronic dry eye.
Is it FDA-approved?
Editor’s note
Status: Yes. The FDA approved cyclosporine and two later formulations on this timeline: Year | FDA approval 1983 | Cyclosporine, for transplant rejection 1995 | Neoral microemulsion 2002 | Restasis eye drop The systemic formulations carry boxed warnings, including for kidney toxicity and for the increased risk of serious infections and malignancies (especially lymphoma and skin cancer) that comes with immunosuppression.
Category: FDA-approved · Primary body area: Immune & defense
Yes. The FDA approved cyclosporine and two later formulations on this timeline:
| Year | FDA approval |
|---|---|
| 1983 | Cyclosporine, for transplant rejection |
| 1995 | Neoral microemulsion |
| 2002 | Restasis eye drop |
The systemic formulations carry boxed warnings, including for kidney toxicity and for the increased risk of serious infections and malignancies (especially lymphoma and skin cancer) that comes with immunosuppression.
What is cyclosporine prescribed for?
Systemic cyclosporine is prescribed to prevent rejection in kidney, liver, and heart transplants, and for severe rheumatoid arthritis and severe plaque psoriasis that have not responded to other treatment. Restasis is prescribed to increase tear production in chronic dry eye associated with inflammation. The different oral products are not freely interchangeable and require monitoring.
What are the side effects?
According to the prescribing information, common side effects of systemic use include:
- High blood pressure
- Kidney impairment with rising creatinine
- Tremor
- Excess hair growth and gum overgrowth
More serious considerations include:
- Boxed warnings for kidney toxicity and for increased risk of serious infections and cancers, including lymphoma and skin cancer
- The need for blood-level monitoring and attention to many drug interactions
- Restasis, acting locally, mainly causes eye burning or stinging and does not carry these systemic warnings
Sources: FDA prescribing information for Sandimmune, Neoral, and Restasis; the Canadian Multicentre Transplant Study (The New England Journal of Medicine, 1983, DOI: 10.1056/NEJM198310063091401), indexed on PubMed. This document is educational and does not constitute medical advice.
Registered human trials
0 registered human trials on ClinicalTrials.gov that we reviewed
Sources
- [1]
Compare every peptide’s status in the peptide regulatory status database
More for Immune & defense
View all immune & defense peptides →- In clinical trials Immune & defense
Aviptadil
Aviptadil is a synthetic form of vasoactive intestinal peptide (VIP), a signaling molecule that acts on lung receptors, and it has been studied mainly for severe COVID-19 respiratory failure. In the NIH-funded TESICO trial of 461 patients, aviptadil did not beat placebo on the 90-day recovery scale (odds ratio 1.11, 95% CI 0.80 to 1.55, p = 0.54). Ninety-day mortality was 38% with aviptadil versus 36% with placebo (p = 0.78), and the trial stopped early for futility. As of 2026 it is not FDA-approved for any use.
- FDA-approved Immune & defense
Enfuvirtide
Enfuvirtide (formerly sold as Fuzeon) is a peptide HIV drug that blocks the virus from entering CD4 immune cells, the first of the so-called fusion inhibitors. It was used in treatment-experienced patients whose virus is no longer controlled by other antiretrovirals. It was FDA-approved in the U.S. in 2003, but Fuzeon was discontinued there in February 2025.
- Not FDA-approved Immune & defense
Ll-37
LL-37 is the body's natural antimicrobial "host-defense" peptide, intensely studied as part of the immune system and sold on the "research peptide" market for antimicrobial and immune support. Its biology is well described, but there is no approved product and no human efficacy evidence for the injected wellness use, and its effects are context-dependent. As of 2026 it is not FDA-approved.
- In clinical trials Immune & defense
Murepavadin
Murepavadin is an investigational antimicrobial peptidomimetic that targets a protein unique to Pseudomonas aeruginosa, developed by Polyphor for serious lung infections. Its intravenous Phase 3 program was halted after an unexpected rate of kidney injury, and later inhaled development did not mature. As of 2026 it is not approved.
- In clinical trials Immune & defense
Nangibotide
Nangibotide is an investigational peptide that inhibits the inflammatory receptor TREM-1, developed by Inotrem as an intravenous treatment for septic shock. Its Phase 2b trial did not meet its primary endpoint, though a signal appeared in a subgroup of patients with high levels of a related biomarker. As of 2026 it is not approved.
- FDA-approved Immune & defense
Polymyxin-B-Colistin
Polymyxin B and colistin (colistin is also called polymyxin E) are older cyclic lipopeptide antibiotics that have returned to use as last-resort treatments for multidrug-resistant Gram-negative infections. They punch holes in the bacterial outer membrane but carry meaningful kidney and nerve toxicity. Both have long been FDA-approved in the U.S. and are reserved for serious infections with few other options.