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Trelstar

triptorelin pamoate
Used for Prostate Cancer
Used for Prostate Cancer

Trelstar (triptorelin) is a prescription injection used to treat advanced prostate cancer. It’s part of a group of medications called gonadotropin-releasing hormone (GnRH) agonists, also known as androgen deprivation therapy (ADT). This injection works by lowering testosterone levels, which helps slow down the growth of prostate cancer. You’ll get the injection in the buttock muscle every once a month, every 3 months, or every 6 months, depending on your dose. Common side effects include hot flashes, bone pain, and headache.

Reviewed by:
reviewer
Julia Lee, PharmD, BCOP
reviewer
Daisy Chau, PharmD
Last reviewed on September 22, 2025
BasicsSide effectsPros & consPharmacist tipsFAQsWarningsDosageInteractionsAlternativesLatest newsPricesMedicare
basics-icon

What is Trelstar (triptorelin)?

What is Trelstar (triptorelin) used for?

How Trelstar (triptorelin) works

Trelstar (triptorelin) is a gonadotropin-releasing hormone (GnRH) agonist, a lab-made version of the natural hormone GnRH. Normally GnRH tells your body to make testosterone, which can fuel prostate cancer growth.

When you first start Trelstar (triptorelin), it can briefly cause your body to make more testosterone. But after a few weeks, it switches gears and tells your body to stop making testosterone. By lowering testosterone, this medication helps slow down the growth and spread of prostate cancer.

Are you looking for information on Triptodur (triptorelin) for precocious puberty instead?

Drug Facts

Common BrandsTrelstar
Drug ClassGnRH agonist
Controlled Substance ClassificationNot a controlled medication
Generic StatusNo lower-cost generic available
AvailabilityPrescription only
basics-icon

What are the side effects of Trelstar (triptorelin)?

The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.

Common Side Effects

3.75 mg:
  • Hot flashes (59%)
  • Bone pain (12%)
  • Erectile dysfunction (7%)
11.25 mg:
  • Hot flashes (73%)
  • Bone pain (13%)
  • Headache (7%)
22.5 mg:
  • Hot flashes (73%)
  • Flu infection (16%)
  • High blood pressure (14%)
  • Urinary tract infection (12%)
  • Back pain (11%)
  • Erectile dysfunction (10%)

Other Side Effects

3.75 mg:
  • Headache
  • Tiredness
  • Dizziness
  • Diarrhea
  • Trouble sleeping
11.25 mg:
  • Pain at the injection site
  • Dizziness
  • Nausea
  • Swelling in the legs
  • Erectile dysfunction
  • Painful urination
22.5 mg:
  • Swelling in the arms and legs
  • Bronchitis
  • Rise in blood sugar
  • Joint pain
  • Headache
  • Trouble sleeping
  • Trouble urinating

Serious Side Effects

Contact your healthcare provider immediately if you experience any of the following.
  • Serious allergic reaction: rash, swelling of the face or throat, trouble breathing
  • Heart attack: chest pain, shortness of breath, rapid breathing, sweating, fatigue, dizziness, nausea, vomiting
  • Heart rhythm problems: fast or uneven heartbeat, fainting, dizziness
  • Stroke: sudden numbness or weakness, confusion, trouble talking, trouble seeing, dizziness, trouble walking
  • Seizure: sudden jerking or shaking, loss of consciousness, confusion, trouble speaking

Source: DailyMed

The following side effects have also been reported

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur:

More common

For children

Diarrhea

loss of appetite

nausea

stomach pain

weakness

Less common

For children

Anxiety

body aches or pain

chills

cough

cough producing mucus

difficulty with breathing

ear congestion

fever

general feeling of discomfort or illness

headache

joint pain

loss of voice

mood or mental changes, including abnormal crying, aggression, agitation, delusions, irritability, nervousness, or restlessness

muscle aches and pains

nasal congestion

runny nose

shivering

sneezing

sore throat

sweating

tightness in the chest

trouble sleeping

unusual tiredness or weakness

vomiting

For adult men

Bladder pain

bloating or swelling of the face, arms, hands, lower legs, or feet

bloody or cloudy urine

blurred vision

chest pain

cough producing mucus

decrease in urine volume or frequency of urination

difficult or labored breathing

difficult, burning, or painful urination

difficulty in passing urine

dizziness

dry mouth

flushed, dry skin

frequent urge to urinate

fruit-like breath odor

headache

increased hunger

increased thirst

increased urination

loss of consciousness

lower back or side pain

nausea

nervousness

pale skin

pounding in the ears

rapid weight gain

slow or fast heartbeat

stomach ache

sweating

tightness in the chest

tingling of the hands or feet

troubled breathing

troubled breathing with exertion

unexplained weight loss

unusual bleeding or bruising

unusual tiredness or weakness

unusual weight gain or loss

vomiting

Incidence not known

For children

Blurred or loss of vision

depression

difficulty with swallowing

disturbed color perception

dizziness

double vision

halos around lights

hives, itching, skin rash

nervousness

night blindness

overbright appearance of lights

pounding in the ears

puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue

seizures

slow or fast heartbeat

thoughts of killing oneself

For adult men

Anxiety

changes in skin color

changes in vision

chest discomfort

cold, clammy, or pale skin

confusion

dizziness or lightheadedness

fainting

inability to speak

irregular heartbeat

numbness or tingling in the face, arms, or legs

pain

pain or discomfort in the arms, jaw, back, or neck

pain, redness, or swelling in the arm or leg

seizures

severe or sudden headache

slow heart rate

slurred speech

sudden shortness of breath or troubled breathing

temporary blindness

tenderness

trouble speaking, thinking, or walking

weakness in the arm or leg on one side of the body, sudden and severe

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For children

Bleeding, blistering, burning, coldness, discoloration of skin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site

stuffy or runny nose

For adult men

Bone pain

chills

decrease in testicle size

decreased interest in sexual intercourse

diarrhea

feeling of warmth or redness of the face, neck, arms, and occasionally, upper chest

fever

general feeling of discomfort or illness

inability to have or keep an erection

joint pain

leg pain

loss in sexual ability, desire, drive, or performance

loss of appetite

muscle aches and pains

redness of the face, neck, arms, and occasionally, upper chest

runny nose

shivering

sore throat

sudden sweating

trouble sleeping

Less common

For children

Change in hearing

dryness or soreness of the throat

ear drainage

earache

hoarseness

itching of the ears

pain or tenderness around the eyes and cheekbones

tender, swollen glands in the neck

voice changes

For adult men

Back pain

belching

body aches or pain

breast pain

burning, dry, or itching eyes

congestion

crying

depersonalization

difficulty having a bowel movement

difficulty with moving

discharge or excessive tearing

dysphoria

euphoria

eye pain

heartburn

hoarseness

indigestion

injection site pain

itching or rash

lack or loss of strength

leg cramps

loss of appetite

muscle aching or cramping

muscle pains or stiffness

paranoia

quick to react or overreact emotionally

rapidly changing moods

redness, pain, or swelling of the eye, eyelid, or inner lining of the eyelid

runny nose

stomach discomfort, upset, or pain

swelling of the breasts or breast soreness in both females and males

swollen joints

tender, swollen glands in the neck

trouble swallowing

voice changes

weight loss

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

pros-and-cons

Pros and cons of Trelstar (triptorelin)

thumbs-up

Pros

Injected once every 1, 3, or 6 months

Helps lower testosterone to slow cancer progression

Recommended hormone therapy for prostate cancer

thumbs-down

Cons

Injections must be given by a healthcare professional

Can cause a temporary rise in testosterone at first (flare)

Raises the risk of heart problems and diabetes

pharmacist-tips

Pharmacist tips for Trelstar (triptorelin)

pharmacist

  • You will get Trelstar (triptorelin) as an injection in the buttock at your clinic. The shots are given on alternating sides each time to help reduce irritation.

    • In the first few weeks after your Trelstar (triptorelin) injection, you might have a tumor flare, which means your prostate cancer symptoms can temporarily get worse. If symptoms such as bone pain, bladder pain, or trouble urinating continue after the first few weeks, tell your oncologist right away.

      • You will usually keep taking Trelstar (triptorelin) even if your prostate cancer spreads to other parts of your body. Your oncologist might add other medications to your treatment at that point.

        • Trelstar (triptorelin) can raise your risk of heart problems such as heart attack or stroke. Call your care team right away if you notice chest pain, shortness of breath, dizziness, weakness on one side, or trouble speaking.

          • Trelstar (triptorelin) might cause seizures in some people. Contact your care team immediately if you have a seizure.

            faqs

            Frequently asked questions about Trelstar (triptorelin)

            Is Trelstar (triptorelin) chemotherapy?
            No, Trelstar (triptorelin) isn’t chemotherapy. Chemotherapy works by directly killing fast-growing cells, including cancer cells. Trelstar (triptorelin) is a type of hormone therapy that lowers testosterone, the hormone that helps prostate cancer grow. By reducing testosterone, Trelstar (triptorelin) helps slow down the cancer’s growth and spread.
            Can Trelstar (triptorelin) affect your heart?
            Yes, Trelstar (triptorelin) can affect your heart. It can raise your risk of heart problems like heart attack, stroke, or irregular heartbeat. Your oncologist will check your heart health, especially if you already have heart problems. Tell your care team right away if you notice chest pain, shortness of breath, dizziness, or a fast or uneven heartbeat while taking this medication.
            How long can I take Trelstar (triptorelin) for my prostate cancer?
            It could be quite some time. Testosterone is an important hormone that prostate cancers use to grow and spread. Even if your prostate cancer spreads to other parts of your body while you are taking Trelstar (triptorelin), it’s likely that your oncologist will have you continue the medication to keep testosterone levels low.
            How long does Trelstar (triptorelin) take to work?
            When you first start Trelstar (triptorelin), your testosterone levels can rise for a short time. This is often called a testosterone flare, and it usually lasts for the first few weeks of treatment. After that, your testosterone levels will drop significantly, which helps slow the growth of prostate cancer.
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            warings-icon

            What are the risks and warnings for Trelstar (triptorelin)?

            Trelstar (triptorelin) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.

            risk-warning

            Allergic reactions

            • Risk factors: Previous allergic reaction to other GnRH agonists

              In rare cases, people had allergic reactions to Trelstar (triptorelin). Tell your oncologist if you’ve had a reaction to similar medications like Lupron (leuprolide) or Zoladex (goserelin). Get medical help right away if you notice itching, swelling, or trouble breathing after getting your injection.

              risk-warning

              Tumor flare

              At the start of treatment, Trelstar (triptorelin) can cause your testosterone levels to rise for a short time, which can make prostate cancer symptoms worse during the first few weeks. After that, your testosterone levels should drop, and your symptoms should improve. Tell your oncologist if you still have bone pain, nerve problems, blood in your urine, or trouble emptying your bladder after about a month of treatment.

              risk-warning

              Risk of high blood sugar, diabetes, high cholesterol, and liver problems

              Taking Trelstar (triptorelin) can cause changes in your metabolism, such as high blood sugar, diabetes, or high cholesterol. Some people have also developed liver problems. If you already have diabetes, your blood sugar might be harder to control. Your care team will check your blood work regularly while you’re taking this medication and treat any changes as needed.

              risk-warning

              Heart attack and stroke

              Taking Trelstar (triptorelin) can raise your risk of heart problems such as heart attack, stroke, or even heart-related death. Your care team will watch for warning signs, but it’s important that you tell them right away if you notice chest pain, shortness of breath, dizziness, weakness on one side, or trouble speaking.

              risk-warning

              Seizures

              • Risk factors: Epilepsy | Brain tumors | Taking other medications that raise the risk for seizures

                Seizures have happened in some people taking Trelstar (triptorelin). They can if you have risk factors like epilepsy, brain tumors, or if you take medications that raise your risk for seizures. But they also can happen without any known risks. If you have a seizure while taking Trelstar (triptorelin), let your care team know immediately.

                risk-warning

                Heart rhythm problems

                • Risk factors: Heart rhythm problems | Heart failure | Electrolyte imbalances | Taking other medications that affect heart rhythm

                  Taking Trelstar (triptorelin) can affect your heart rhythm. Your risk is higher if you’ve had heart rhythm problems, heart failure, electrolyte imbalances, or if you take medications that also affect heart rhythm. Your care team might check your heart rhythm with an electrocardiogram (EKG or ECG) and monitor your electrolytes to make sure any imbalances are corrected.

                  risk-warning

                  Harm to unborn baby

                  Based on how the medication works, Trelstar (triptorelin) might cause harm to an unborn baby. The medication can also cause infertility. If you plan to father a child during your treatment, talk with your oncologist before starting Trelstar (triptorelin).

                  dosage

                  Trelstar (triptorelin) dosage forms

                  Typical dosing for Trelstar (triptorelin)

                  Trelstar (triptorelin) is given as an injection into the buttock muscle. It comes in 3 different strengths, each given at different time intervals:

                  • 3.75 mg (1 month): Injected once every 4 weeks.

                  • 11.25 mg (3 month): Injected once every 12 weeks.

                  • 22.5 mg (6 month): Injected once every 24 weeks.

                  interactions

                  Interactions between Trelstar (triptorelin) and other drugs

                  Trelstar (triptorelin) may interact with certain medications or supplements. Always let your doctor and pharmacist know about any other medications or supplements (including prescribed and over-the-counter medications, vitamins, and dietary or herbal supplements) that you are currently taking. The list below does not include all possible drug interactions with Trelstar (triptorelin). Please note that only the generic name of each medication is listed below.

                  Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are receiving this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

                  Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

                  Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

                  alternatives

                  What are alternatives to Trelstar (triptorelin)?

                  There are a number of medications that your doctor can prescribe in place of Trelstar (triptorelin). Compare a few possible alternatives below.
                  Trelstar (triptorelin)
                  Used for:
                  View Prices
                  Leuprolide acetate
                  Used for:

                  • Advanced prostate cancer

                  View Prices
                  Zoladex (goserelin)
                  Used for:

                  • Prostate cancer

                  • Advanced hormone-receptive positive (HR+) breast cancer

                  • Endometriosis

                  • Endometrial thinning before endometrial ablation

                  $1142.44 Lowest GoodRx priceView Prices

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