What drug do you take to prevent rejection of a donor organ? A Guide to Immunosuppressants

October 11, 2025 •

4 min read

Thanks to modern medications, one-year survival rates for transplanted organs have improved to 95%, with rejection rates as low as 10-15% [1.2.1]. If you are wondering, what drug do you take to prevent rejection of a donor organ, the answer is a class of drugs called immunosuppressants, which are crucial for success.

Quick Summary

After an organ transplant, patients must take lifelong medications called immunosuppressants. These drugs work by lowering the body's immune response to stop it from attacking the new, foreign organ. This overview details the main types, side effects, and costs.

Key Points

Lifelong Medication is Necessary: Transplant recipients must take immunosuppressant (anti-rejection) drugs for the life of the organ to prevent their immune system from attacking it [1.11.3].
Combination Therapy is Standard: Regimens typically involve a combination of drugs from different classes, such as calcineurin inhibitors, antiproliferatives, and corticosteroids, to achieve effective suppression with fewer side effects [1.7.2].
Main Classes of Drugs: The primary classes of anti-rejection drugs include Calcineurin Inhibitors (e.g., Tacrolimus), Antiproliferatives (e.g., Mycophenolate), mTOR inhibitors (e.g., Sirolimus), and Corticosteroids (e.g., Prednisone) [1.4.5].
Significant Side Effects: All immunosuppressants have potential side effects, including an increased risk of infection, kidney problems, high blood pressure, diabetes, and certain cancers [1.5.1].
Phased Approach: Immunosuppression is managed in phases: an intense 'induction' phase around surgery, a lifelong 'maintenance' phase, and specific treatment if rejection occurs [1.11.1].
Regular Monitoring is Crucial: Patients require regular blood tests to ensure drug levels are in the therapeutic range—high enough to prevent rejection but low enough to minimize toxicity [1.5.4].
High Cost: Anti-rejection medications are very expensive, potentially costing thousands of dollars per month without comprehensive insurance coverage [1.9.2].

The Critical Role of Anti-Rejection Medication

Following an organ transplant, the recipient's immune system recognizes the new organ as a foreign invader and mounts an attack, a process known as rejection [1.11.4]. To prevent this, patients must take a lifelong regimen of drugs called immunosuppressants, or anti-rejection medications [1.11.3]. These powerful drugs work by weakening the immune system just enough to allow the body to accept the donor organ without leaving the patient completely vulnerable to infections [1.4.2]. The development of these medications has dramatically improved transplant outcomes, with acute rejection rates for kidney transplants, for example, dropping from over 50% in the 1970s to around 10-20% today [1.2.3].

Immunosuppressive therapy is typically divided into three phases [1.11.1]:

Induction Therapy: This involves a potent course of medication administered right before, during, or immediately after the transplant surgery [1.8.2]. The goal is to provide a strong level of immunosuppression when the risk of acute rejection is highest [1.7.2]. Agents like basiliximab or anti-thymocyte globulin are often used [1.3.2].
Maintenance Therapy: This is the lifelong, daily regimen of drugs that transplant recipients must take to prevent rejection over the long term [1.7.1]. It usually involves a combination of several drugs from different classes to maximize effectiveness and minimize side effects [1.7.2].
Treatment of Rejection: If the body begins to reject the organ despite maintenance therapy, higher doses or different types of immunosuppressants are used to stop the rejection episode [1.11.1].

Major Classes of Immunosuppressant Drugs

Maintenance therapy typically combines drugs from at least two or three of the following classes to target the immune system in different ways [1.4.5, 1.7.2].

Calcineurin Inhibitors (CNIs)

This class is a cornerstone of most anti-rejection regimens [1.4.5]. CNIs work by blocking a protein called calcineurin, which in turn inhibits the production of interleukin-2, a substance that activates T-cells—the primary drivers of organ rejection [1.4.4].

Examples: Tacrolimus (Prograf®, Astagraf XL®, Envarsus XR®) and Cyclosporine (Neoral®, Sandimmune®, Gengraf®) [1.3.5].
Side Effects: CNIs can be tough on the kidneys (nephrotoxicity), and may also cause high blood pressure, high cholesterol, tremors, and an increased risk of developing diabetes after transplant [1.5.2, 1.6.3]. Tacrolimus is generally considered more potent but may have a higher incidence of new-onset diabetes compared to cyclosporine [1.6.3].

Antiproliferative Agents (Antimetabolites)

These drugs work by preventing immune cells like T-cells and B-cells from multiplying [1.11.1]. They are almost always used in combination with a CNI [1.4.5].

Examples: Mycophenolate Mofetil (CellCept®), Mycophenolic Acid (Myfortic®), and Azathioprine (Imuran®) [1.3.5].
Side Effects: The most common side effects are gastrointestinal, including diarrhea, nausea, and stomach upset [1.5.2]. They can also lower white blood cell and platelet counts [1.5.2]. Mycophenolate products are known to increase the risk of birth defects and pregnancy loss [1.3.5].

mTOR Inhibitors

Named for their mechanism of inhibiting the 'mammalian target of rapamycin,' these drugs block a different pathway involved in T-cell activation and proliferation [1.6.1]. They are often used as an alternative for patients who cannot tolerate the kidney-related side effects of CNIs [1.3.5].

Examples: Sirolimus (Rapamune®) and Everolimus (Zortress®) [1.3.5].
Side Effects: Common side effects include high cholesterol and triglycerides, delayed wound healing, mouth sores, and swelling [1.5.2].

Corticosteroids

These are powerful anti-inflammatory drugs that suppress the immune system in a broad, non-specific way [1.4.4].

Example: Prednisone [1.3.1].
Side Effects: While effective, long-term use is associated with many side effects, including weight gain, mood swings, high blood sugar, high blood pressure, osteoporosis (bone loss), and cataracts [1.5.2, 1.10.4]. Due to these effects, many transplant centers aim to reduce or eliminate steroid use over time.

Comparison of Common Maintenance Drugs


Drug Class	Common Drugs	Mechanism of Action	Key Side Effects
Calcineurin Inhibitors	Tacrolimus, Cyclosporine	Inhibit T-cell activation by blocking calcineurin [1.4.4]	Kidney damage, high blood pressure, diabetes, tremors [1.6.3]
Antiproliferatives	Mycophenolate, Azathioprine	Prevent multiplication of immune cells [1.11.1]	Diarrhea, nausea, low white blood cell count [1.5.2]
mTOR Inhibitors	Sirolimus, Everolimus	Block a key protein (mTOR) for cell proliferation [1.6.1]	High cholesterol, mouth sores, poor wound healing [1.5.2]
Corticosteroids	Prednisone	Broad anti-inflammatory and immune suppression [1.4.4]	Weight gain, high blood sugar, bone loss, mood swings [1.5.2]

Living with Immunosuppressants

Life after transplant requires strict adherence to the prescribed medication schedule. Missing even a single dose can increase the risk of rejection [1.11.3]. Patients must also be vigilant for side effects and signs of infection, as a suppressed immune system has a harder time fighting off common illnesses [1.5.4].

The financial burden can also be significant. Without insurance, these life-saving medications can cost between $5,000 and $7,000 per month [1.9.1, 1.9.2]. Even with coverage, co-pays can be substantial.

Regular blood tests are essential to monitor drug levels in the body. The goal is to find a balance: enough medication to prevent rejection but not so much that it causes severe side effects or dangerously high levels of immunosuppression [1.5.4].

Conclusion

To answer the question, "What drug do you take to prevent rejection of a donor organ?", there isn't just one. Patients take a carefully balanced, lifelong combination of immunosuppressant drugs. The mainstays of modern therapy include calcineurin inhibitors like tacrolimus, antiproliferative agents like mycophenolate, and often corticosteroids like prednisone [1.3.1, 1.3.2]. These medications are the key to turning organ transplantation from an experimental procedure into a life-saving treatment, allowing hundreds of thousands of people to live longer, healthier lives.

For more information from an authoritative source, you can visit the National Kidney Foundation's guide on Immunosuppressants. [1.3.5]

Frequently Asked Questions

You must take anti-rejection medications for the entire time you have the transplanted organ, which is typically for the rest of your life [1.11.3].

Tacrolimus (a calcineurin inhibitor) is one of the most common and primary anti-rejection medications used in modern transplant regimens, often in combination with mycophenolate and prednisone [1.3.1, 1.3.2, 1.5.5].

Missing doses can lower the drug's concentration in your blood, increasing the risk that your immune system will start to attack and reject the transplanted organ. It is critical to adhere to the prescribed schedule.

You should consult your transplant team before consuming alcohol. It can interact with medications and put extra stress on your liver, which is responsible for processing many of these drugs.

Common long-term side effects include an increased risk of infection, kidney damage, high blood pressure, new-onset diabetes, high cholesterol, and an elevated risk for certain types of cancer [1.5.1, 1.5.4].

Both are calcineurin inhibitors, but they have different chemical structures and side-effect profiles. Tacrolimus is generally more potent, while cyclosporine may cause more cosmetic side effects like gum swelling and hair growth. Tacrolimus has a higher association with new-onset diabetes [1.5.2, 1.6.3].

Using a combination of drugs allows doctors to target different parts of the immune response simultaneously. This approach is more effective at preventing rejection and may allow for lower doses of each individual drug, which helps to minimize overall side effects [1.7.2].