Trenbolone, a.k.a. “tren,” is an anabolic steroid similar to testosterone.

Many consider it a high-risk, high-reward substance—a drug that builds “dense” muscle and rapidly strips fat, but that also comes with a litany of adverse side effects often more severe than those of similar substances.

The side effects of tren are debated but have shown to include the following:

  • Liver Toxicity
  • Hormonal Imbalance
  • Heart Disease
  • Mental Health Issues
  • Fertility Issues
  • Sleep Issues
  • Tren Cough

If you’re curious to learn more about the uses and side effects of tren, this article is for you.

What Is Trenbolone?

Trenbolone, commonly known as “tren,” is a potent anabolic-androgenic steroid (AAS) derived from nandrolone, another well-known synthetic steroid.

Its name comes from its chemical structure: tri-en, 17b-ol, 3-one.

Scientists created trenbolone in the 1960s to boost cattle’s appetite and muscle growth and reduce their body fat before slaughter. Today, ranchers still use it for livestock under the brand name Finaplix-H.

In 1980, a French pharmaceutical company introduced Parabolan, a human form of tren, aimed at treating muscle wasting conditions, AIDs, and osteoporosis. Around this time, tren became popular with bodybuilders and athletes because of its powerful effects on muscle growth, strength, and fat loss.

However, the market withdrew Parabolan in 1987 due to significant adverse side effects.

Since then, all trenbolone for human use has come from illegal production in underground labs worldwide.

Find the Perfect Supplements for You in Just 60 Seconds

You don't need supplements to build muscle, lose fat, and get healthy. But the right ones can help. Take this quiz to learn which ones are best for you.

Take the Quiz

What Does Trenbolone Do?

Muscle Growth

Trenbolone binds to androgen receptors throughout your body, triggering a range of effects that help you build muscle:

  • Increased Protein Synthesis: Tren significantly increases protein synthesis rates. Protein synthesis is the process by which cells build proteins, the building blocks of muscle tissue. This leads to increased muscle gains and strength. 
  • Increased Insulin-like Growth Factor 1: Tren stimulates insulin-like growth factor 1 (IGF-1) production in the body, greatly increasing your body’s ability to build lean muscle.
  • Enhanced Nitrogen Retention: Trenbolone improves nitrogen retention in muscle tissue. Muscles are mainly composed of protein, and protein is composed of amino acids, which contain nitrogen. By enhancing nitrogen retention, tren helps to maintain a positive nitrogen balance within the muscles, creating a more anabolic environment in the body.
  • Reduction in Glucocorticoid Hormones: Glucocorticoid hormones (such as cortisol) are catabolic hormones, meaning they break down muscle tissue. Trenbolone reduces glucocorticoid hormone levels, decreasing muscle breakdown and promoting muscle growth. 
  • Increased Red Blood Cell Production: Tren can stimulate red blood cell production, enhancing oxygen delivery to muscles and improving physical performance. 

Fat Loss

Tren also influences fat burning. Scientists attribute its fat-loss effects to the following mechanisms:

  • Increased Fat Mobilization: Trenbolone activates androgen receptors in adipose (fat) tissue, leading to its breakdown. 
  • Influencing Stem Cell Development: It may alter the path of mesenchymal pluripotent stem cells, steering them towards becoming muscle cells rather than fat cells. This process inhibits the formation of new fat cells and promotes muscle gains.
  • Enhancing Fat Metabolism: Trenbolone stimulates liver enzymes involved in fat metabolism, such as enoyl-coA-hydratase and acyl-coA-dehydrogenase, suggesting increased fat breakdown at the molecular level.

Find the Best Diet for You in Just 60 Seconds

How many calories should you eat? What about "macros?" What foods should you eat? Take our 60-second quiz to get science-based answers to these questions and more.

Take the Quiz

Trenbolone Side Effects

Tren is notorious for having more severe side effects than other steroids.

For anyone thinking about using trenbolone, it’s vital to have a comprehensive understanding of its potential effects on the body. It’s also important to note that there are no human studies exploring trenbolone’s side effects.

Our understanding primarily comes from animal studies and anecdotal reports from bodybuilders and athletes who have used it.

Below is an overview of the most commonly reported trenbolone side effects, as observed in animal studies and shared by users in the fitness community.

Liver Toxicity

It’s not yet clear whether tren has a detrimental effect on liver health. While some anecdotal evidence suggests it carries minimal risk, other research shows it can cause severe liver toxicity, which can lead to symptoms such as fatigue, nausea, abdominal pain, confusion, cerebral edema (swelling of the brain), sepsis, multiorgan failure, and, in some cases, death.

Therefore, it’s wise to be cautious about tren’s effects on the liver until further research provides clearer insights.

“Tren Cough”

Many tren steroid users experience a violent coughing fit known as “tren cough” during or shortly after injecting the compound.

The exact cause of tren cough remains unknown, though many believe it occurs because the high androgenic activity of tren activates signaling molecules in your body called prostaglandins.

These prostaglandins cause inflammation, which narrows blood vessels. When this narrowing affects the lung’s bronchial tubes, your body responds by coughing.

Hormone Imbalance

Using tren steroids disrupts the body’s hypothalamic-pituitary-gonadal axis (HPG axis), a hormonal system responsible for producing sex hormones.

Research shows that trenbolone reduces luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone levels, which, in turn, can reduce testicle size. 

The exact way tren interferes with the HPG axis is not entirely clear, but it might be related to its direct effects on the hypothalamus (the area of the brain responsible for managing hormones) or its impact on hormone production in the testes.

You may be able to limit these effects by using “post-cycle therapy,” a pharmaceutical-based protocol that helps correct the negative hormonal effects of trenbolone and other performance-enhancing drugs.

Androgenic Effects

Studies show that men who take AASs commonly report a surge in sexual drive, as well as acne, increased body hair growth, and heightened aggression.

Additionally, they may experience fluid retention, elevated blood pressure, trouble sleeping, irritability, libido fluctuations, an uptick in appetite, excessive sweating, mood swings, hair loss, and gynecomastia.

For female athletes, the data is less conclusive. Available evidence suggests that women may experience a lowering of their voice, growth of facial hair, clitoral enlargement, a rise in aggressiveness, and changes in appetite.

Other side effects observed in women include acne, fluid retention, and changes in libido. 

It’s important to note that the severity and type of side effects associated with tren’s anabolic and androgenic activity can vary depending on the dosages and duration of use.

Heart Disease

AASs, like tren, can negatively affect cholesterol levels.

They often lower HDL (“good”) cholesterol and raise LDL (“bad”) cholesterol, increasing the risk of numerous cardiovascular conditions, such as arteriosclerosis. 

Because of its structure and resistance to breakdown, tren has a moderate-to-strong negative impact on cholesterol levels and heart disease risk.

It can also raise blood pressure and triglycerides, reduce the flexibility of blood vessels, and contribute to heart muscle enlargement, all of which raise the risk of heart disease and heart attacks over the long term. 

Mental Health Issues

Tren users typically report feeling significantly more aggressive.

For example, in a study conducted by Griffith University, tren steroid users reported having significantly less patience while “on cycle.” They also recounted how the “tren-version” of themselves was more prone to aggressive outbursts, which often had negative effects on their relationships with friends and family.

Sleep Issues

A common problem for people using trenbolone is poor sleep, often referred to as “trensomnia.”

Although the cause of trensomnia is unclear, some research suggests it may be because trenbolone increases the levels of a brain chemical known as hypocretin, which is responsible for keeping us awake.

Fertility Issues

Most evidence suggests tren is unlikely to cause birth defects.

However, studies show it may reduce female fertility, cause changes in females’ reproductive organs, and disrupt ovulation.

It’s less clear how trenbolone affects fertility in males, though animal research tends to suggest it can have negative effects. For example, in a study published in the journal Chemosphere, scientists found that trenbolone delayed puberty and disrupted regular sexual behavior in quails exposed to trenbolone.

Are Tren “Before and After” Pictures Real?

Here’s an example of one of the many tren “before and after” photos that you can find online:

Trenbolone Before and After

While these pictures likely depict people who have taken tren, attributing all of their results to trenbolone is unwise.

It’s possible that the people in these photos have used favorable lighting and angles and photo editing to make their results seem more impressive. Additionally, many of the individuals in these pictures will be using other steroids besides trenbolone, making it impossible to know how much tren contributed to their results.

Moreover, these photos only showcase physical improvements, glossing over the potential health implications of using tren. While individuals might look more muscular after a trenbolone cycle, their overall health may have deteriorated.

Some Nutritionists Charge Hundreds of Dollars for This Diet "Hack" . . .

. . . and it's yours for free. Take our 60-second quiz and learn exactly how many calories you should eat, what your "macros" should be, what foods are best for you, and more.

Take the Quiz

Trenbolone Cycles and Use

Trenbolone is highly effective for building muscle and losing fat, which is why bodybuilders and athletes commonly use it during both bulks and cuts

Cycling Trenbolone While Bulking

Despite being a powerful muscle-building steroid, trenbolone isn’t as effective for gaining mass as steroids with higher “estrogenic activity.”

Estrogenic activity refers to a steroid’s tendency to mimic or promote the effects of estrogen, the female sex hormone.

Steroids with high estrogenic activity boost muscle growth through several mechanisms:

  • They improve how your body uses glucose to build and repair muscle.
  • They increase the production of anabolic hormones, including growth hormone and insulin-like growth factor-1 (GF-1).
  • They boost the concentration of androgen receptors in muscle tissue.
  • They help you avoid “steroid fatigue,” a lethargy many steroid users experience when they suppress estrogen, which can hinder training intensity and, thus, muscle and strength gain.

As such, bodybuilders and athletes who use trenbolone during bulks typically “stack” it with other compounds with higher estrogenic activity that promote more drastic growth.

Cycling Trenbolone While Cutting

Trenbolone attaches to catabolic hormone receptors, blocking muscle breakdown. Its ability to prevent muscle loss makes it popular among bodybuilders and athletes who prioritize muscle preservation while dieting for a show or competition.

Tren also enhances how the body “partitions” nutrients.

In other words, it changes the process by which the body decides whether to use nutrients for building muscle, storing fat, or for other metabolic functions. As a result, tren can directly contribute to fat loss. 

Moreover, trenbolone strongly binds to androgen receptors in fat cells, further boosting fat loss.

FAQ #1: Trenbolone vs. Testosterone: What’s the difference?

Because they’re both powerful anabolic steroids, many people like to compare trenbolone vs testosterone

However, evidence suggests trenbolone has a few unique advantages over testosterone.

For instance, research shows that tren binds to androgen receptors with three times the affinity of testosterone and has five times the anabolic strength, making it even more effective at promoting muscle growth.

What’s more, it exerts fewer androgenic effects than testosterone, so it’s less likely to cause unwanted side effects, such as hair loss, body hair growth, prostate growth, oily skin, and acne. Importantly, these side effects are still very common among “trenners.”

Additionally, unlike “T,” trenbolone doesn’t convert to estrogen in the body and generally doesn’t cause estrogen-like effects.

That said, it does bind strongly to the progesterone receptor, which can lead to side effects similar to estrogen’s in some cases.

It can also increase the risk of gynecomastia (development of male breasts), especially when combined with other steroids that convert to estrogen.  

FAQ #2: Is trenbolone safe?

While trenbolone is a powerful anabolic steroid known for boosting muscle growth and fat loss, its safety is a concern.

Tren steroids can cause severe side effects like increased aggression, poor cardiovascular health, and potential liver toxicity. It can also hinder sleep and affect the body’s hormonal balance, leading to issues like increased body hair, acne, and changes in libido.

Women may also become more “masculine” while using trenbolone, experiencing side effects such as deepening of the voice and facial hair growth.

Additionally, trenbolone can impact mental health, causing mood swings and irritability.

Therefore, trenbolone is generally not considered safe.

In the United States, trenbolone is classified as a “Schedule III” substance under the Controlled Substances Act. This means it is illegal to use, possess, buy, or sell trenbolone without a prescription from a licensed healthcare provider. 

FAQ #4: What is tren steroid’s worst side effect?

Tren steroid use comes with a wide range of serious side effects. Among the most severe is its potential impact on long-term cardiovascular health, including an increased risk of heart disease due to its ability to raise bad cholesterol levels (LDL) while lowering good cholesterol levels (HDL). 

+ Scientific References