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What Is Triptorelin (Trelstar)?


Trelstar (triptorelin) is a Gonadotropin Releasing Hormone (GnRH) agonist (or LHRH agonist). It is indicated for use as a palliative treatment option for individuals with advanced prostate cancer. Trelstar is administered as an intramuscular injection in the buttocks. Individuals taking Trelstar should be closely monitored, especially during the first several weeks of treatment, as tumor flare can occur. Tumor flare is the worsening of tumor symptoms early on in treatment that can lead to spinal cord compression and other adverse effects. Individuals taking Trelstar should also be monitored for high blood pressure and the development of diabetes, as well as for cardiovascular complications.

What are the ingredients in Trelstar?

The active ingredient in Trelstar is triptorelin, the Gonadotropin-Releasing Hormone (GnRH) agonist.

How does Trelstar work?

Trelstar’s active ingredient is a Gonadotropin-Releasing Hormone (GnRH) agonist. This means, that its purpose is to activate the GnRH receptor by mimicking the receptor’s normal activator. Prostate cancer tumors are often fueled to grow by androgens, including testosterone. Turning off the body’s ability to produce testosterone, or reducing the amount made can potentially halt tumor growth. Trelstar continuously activates a key receptor in the pathway to making testosterone, and eventually overwhelms the receptor. When the receptor is overwhelmed, or desensitized, it decreases making luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are key in making testosterone. This is also known as medical or chemical castration.

However, a major concern with desensitizing the GnRH receptor is that before the receptor becomes overwhelmed, it will be continuously activated for the first few weeks of treatment. This means that more testosterone will be produced than usual, and could potentially cause a short term surge in tumor growth, known as Tumor Flare Phenomenon. Risk of tumor flare can be decreased by taking an antiandrogen with Trelstar.

What are the possible side effects of Trelstar?

Multiple clinical trials evaluated the safety and efficacy of Trelstar. The most common side effects of Trelstar vary with the different dosages administered and include hot flashes, sexual dysfunction, skeletal pain, headache, leg pain and swelling, shrinking of the testicles, and decreased erections. Injection site reactions are also possible while receiving Trelstar. This is not an exhaustive list of all potential side effects of Trelstar. Talk to your healthcare provider or pharmacist for further information.

Things to note about Trelstar

Several rare but more serious side effects can accompany Trelstar including increased blood sugar, hypersensitivity, and injection site reactions. Additionally, Trelstar may increase an individual’s risk of developing diabetes and cardiovascular complications, including an increased risk of heart attack, stroke, and sudden cardiac death. Individuals taking Trelstar should be monitored for any cardiovascular concerns.

Tumor Flare Phenomenon is possible while taking Trelstar, in which tumor growth is accelerated for a short time before it is halted. Alert your provider immediately if you notice any serious signs of Tumor Flare Phenomenon including:

  • Weakness or loss of feeling in legs
  • Have blood in the urine
  • Have trouble urinating or are unable to urinate
  • Experience new or worsening bone pain

You should also contact your provider if you notice any signs of an allergic reaction to the medication, including chest pain or difficulty breathing.

Before starting Trelstar talk to your provider if you:

  • Have any heart or blood vessel conditions such as irregular heart beat
  • Are taking any medications for any cardiovascular conditions
  • Have high blood pressure
  • Are taking any other medications, vitamins, or herbal supplements

Dosing information

Trelstar is administered intramuscularly by a provider in the buttocks. Your doctor will determine the appropriate dosage and administration timeline for you; however, common dosages include 3.75 mg every four weeks, 11.25 mg every 12 weeks, and 22.5 mg every 24 weeks.1

Written by: Casey Hribar | Last reviewed: January 2019
  1. Trelstar Prescribing Information. Jul 2014. Available from:,021288s028,022437s008lbl.pdf