Is Synthol a Steroid? How It Works and Its Risks

Synthol is not a steroid. It contains no anabolic or androgenic compounds. It is a site enhancement oil, a mixture injected directly into muscles to make them look bigger without changing their actual strength or function. Where anabolic steroids work by altering hormone levels to drive real muscle protein synthesis, synthol simply fills space inside or around muscle tissue like a balloon being inflated with liquid. The confusion between the two is understandable since both circulate in bodybuilding culture, but they are fundamentally different substances with very different mechanisms and very different risks.

What Synthol Actually Contains

The standard synthol formula is roughly 85 percent oil, 7.5 percent lidocaine, and 7.5 percent benzyl alcohol.¹ The oil component is typically made up of medium-chain triglycerides, the same type of fatty acid chains found in coconut oil and certain cooking oils. The lidocaine is a local anesthetic included to reduce the pain of injection. The alcohol serves as a sterilizing agent. None of these ingredients have any hormonal activity. One medical review states plainly that “synthol oil does not contain steroids.”²

Steroids, by contrast, are synthetic versions of testosterone or related hormones. They bind to androgen receptors inside cells, switch on genes involved in muscle protein production, and produce system-wide hormonal changes including effects on the liver, cardiovascular system, reproductive organs, and mood. Synthol does none of this. It sits in the muscle as a foreign substance. The body cannot break it down or absorb it in any meaningful way, so the oil simply stays put, sometimes for years or even decades.

Why People Use It Instead of Steroids

The appeal of synthol is almost entirely cosmetic and almost entirely about shortcuts. Competitive and recreational bodybuilders sometimes turn to it to bring a lagging muscle group up to match the rest of their physique, a practice sometimes called “fluffing.”³ If one bicep looks smaller than the other, or the calves are not responding to training, synthol can add visible volume to a targeted spot almost immediately after injection.

Users are often drawn to synthol specifically because it does not produce the hormonal side effects associated with anabolic steroids, such as liver damage, testicular atrophy, acne, mood swings, or cardiovascular strain from altered cholesterol levels.⁴ That perceived safety margin is misleading, though. Synthol trades one set of dangers for a completely different and arguably worse set. The risks are local rather than systemic, but they can be devastating.

How It Creates the Illusion of Muscle

When synthol is injected into a muscle, the oil physically displaces tissue and occupies space. The muscle appears larger because it is, in a purely volumetric sense, but the added size comes from trapped oil rather than from new muscle fibers. The injections do not increase muscular strength or performance and are used solely for cosmetic purposes.⁴ The enlargement is immediate, and users typically inject repeatedly over weeks or months until they reach a size they find satisfying.

Because the human body is unable to assimilate synthol oil, it remains in the muscles for a long time, eventually causing chronic swelling.² This is the core of the problem. With a steroid, the drug is metabolized and cleared from the body over days or weeks. With synthol, the oil is essentially permanent. It does not get processed by the liver or kidneys. It just accumulates, provoking an ongoing immune response as the body tries and fails to deal with a substance it was never designed to handle.

What Happens Inside the Muscle Over Time

The body’s reaction to injected oil follows a predictable sequence that can unfold over months, years, or even decades. Research on intramuscular oil injections describes three broad phases. First comes an initial inflammatory phase lasting up to about six months, where the intensity depends on how much oil was injected. Allergic reactions can occur during this stage, sometimes causing vasculitis, an inflammation of blood vessel walls. A latency phase follows, during which the substance may be reasonably well tolerated by the body. This quiet period can last months to years, and there are documented cases in the medical literature of adverse effects appearing as long as 24 years after injections of mineral oils or liquid silicone.⁵

Eventually, a chronic reaction sets in. The immune system’s macrophages ramp up their attempts to break down the foreign material, but the oil resists the enzymes these cells use. The result is chronic granulomatous inflammation, the same type of immune response the body mounts against other substances it cannot digest. Fibrous tissue forms around pockets of oil, dividing them into small globules. Fatty acids can combine with calcium, leading to calcification. Collagen production ramps up as the body walls off the foreign material, and the injected area gradually hardens. Over time, this can cause skin hardening, subcutaneous nodules, and in severe cases necrosis and disfigurement.⁵

The Specific Complications

The medical literature on synthol reads like a catalog of things that can go wrong when you inject oil into living tissue. The complications fall into several categories, and they range from painful and chronic to immediately life-threatening.

Fibrosis: One of the most common outcomes. The scar tissue that forms around trapped oil can become so dense that the muscle loses normal function. A case report describes a 45-year-old man who developed severe fibrosis and recurrent infections in his pectoral region following synthol injections, requiring surgical intervention.⁶
Oil cysts: Whole-body MRI of one bodybuilder with long-term synthol use revealed more than 100 intramuscular oil cysts and loss of normal muscle anatomy.⁷ The word “irreversible” in the study’s title is not used casually.
Chronic foreign-body reactions: These include painful subcutaneous nodules called paraffinomas or oleomas, where the body encapsulates the oil in hard, irregular plaques.²
Infections: Repeated needle punctures into the same muscle create entry points for bacteria. The oil itself provides a medium where bacteria can thrive while being partially shielded from the immune system.
Pulmonary embolism: If the needle accidentally enters a blood vessel, oil can travel to the lungs, causing embolism and alveolar hemorrhage, a condition comparable to fat embolism.⁸ This is a medical emergency that can be fatal.
Ulceration and migration: The oil does not always stay where it was injected. Erratic migration, tumor formation, granulomatous lesions, and ulceration have all been described in the literature, along with severe lung complications and death.⁹

The resulting volume increase, as one review puts it, “is not related to muscular hypertrophy or any adaptive physiological event, thus having only a suspicious aesthetic effect, as the result is that muscle appearance may no longer present a normal muscle anatomy.”⁹ In many of the extreme cases that surface online, the visual result no longer looks like a muscular physique. It looks distorted, lumpy, and visibly artificial.

Why Synthol Sometimes Gets Lumped in With Steroids

Part of the confusion comes from how synthol is classified in anti-doping and regulatory contexts. It is often grouped alongside steroids under the umbrella of “performance and image enhancing drugs,” even though it enhances neither performance nor, in many doctors’ opinions, the image. Both substances circulate through the same underground supply chains. People who use one often use the other. And the black-market products themselves are frequently mislabeled. An analysis of performance-enhancing drugs confiscated in Italy between 2017 and 2019 found that 15 percent of products had a composition completely different from what was declared on the label, while 10 percent showed cross-contamination with other drugs, mainly testosterone esters, likely from residues in the production line.¹⁰ Eleven percent of confiscated products were not labeled at all.

This contamination issue matters. Someone buying what they believe is a pure site enhancement oil from an underground source could be unknowingly injecting a product that contains steroid residues or other drugs entirely. The lack of pharmaceutical-grade manufacturing, quality control, or labeling in the underground market means that what is in the vial may have little relationship to what the seller claims is in the vial.

Synthol Versus Steroids in Practical Terms

For anyone trying to understand the real difference, the clearest way to think about it is this: steroids are drugs that act on the body’s hormonal system and cause real (if risky) physiological changes, including actual muscle growth. Synthol is inert filler. It is closer in concept to a silicone breast implant than to any drug. The muscle does not grow. The tissue does not adapt. No new protein is synthesized. The body just gets bigger in that spot because you pumped oil into it.

Steroids carry their own serious health risks, from cardiovascular disease to liver toxicity to psychological effects. But at least the mechanism of action involves the body’s own biology doing something it was designed to do, just at an exaggerated level. Synthol asks the body to coexist with a large volume of indigestible oil, and the body’s response over time is inflammation, encapsulation, fibrosis, and sometimes tissue death. There is no dose at which synthol is safe in the way that prescription testosterone can be safe under medical supervision. No physician prescribes synthol for any medical purpose.

Can Synthol Be Removed?

Surgical removal is possible but difficult and often incomplete. The problem is that by the time someone seeks medical help, the oil has typically been encapsulated in dense fibrous tissue that is woven through and around normal muscle fibers. Surgeons describe having to excise hardened masses that have replaced functional muscle tissue. In the case of the 45-year-old man with pectoral fibrosis mentioned earlier, management required surgical intervention for a condition that had caused both structural damage and recurrent infections.⁶ The muscle does not return to normal after the oil is removed. The fibrosis is permanent, and the muscle that was displaced or destroyed by the oil and the body’s immune response does not regenerate.

In the case where MRI revealed more than 100 oil cysts across multiple muscle groups, the findings explicitly described loss of normal muscle anatomy.⁷ The word “irreversible” in the title of that case study captures the prognosis. Surgery can remove some of the oil and fibrotic tissue, reduce the risk of further complications, and improve appearance, but it cannot restore what was there before.

The Online Culture Around Synthol

Synthol occupies an unusual place in bodybuilding culture. Most competitive bodybuilders publicly disavow its use, and extreme synthol use is widely mocked in online fitness communities. The cartoonishly swollen arms and shoulders that go viral periodically are almost universally viewed as grotesque rather than impressive. Yet synthol use persists, driven by a combination of body dysmorphia, accessibility, and a subculture of online information-sharing where users advise one another on injection protocols, dosing schedules, and which muscles respond “best” to oil.

Research into online bodybuilding forums has found that users construct their own expertise around synthol, sharing detailed protocols and reassuring newcomers that the practice is safe when done “correctly.”³ This lay expertise fills the vacuum left by the absence of any medical guidance, since no doctor would recommend the practice. The community-built knowledge base creates an illusion of safety and precision that the medical literature flatly contradicts. There is no established safe protocol for injecting oil into muscle. The complications documented in case reports come from users who believed they were doing it carefully.

Other Site Enhancement Oils

Synthol is the most well-known site enhancement oil, but it is not the only one. Historically, bodybuilders and others seeking to alter their appearance have injected mineral oil, paraffin oil, sesame oil, and even silicone into muscles and soft tissue. The complications are broadly similar across all these substances. The body treats them all as foreign material, and the inflammatory cascade that follows is driven by the same inability to break down and clear the oil. Paraffinomas have been documented after injections of paraffin, mineral oil, and vegetable oils alike.⁹

The medium-chain triglyceride oil in synthol was chosen partly because it was thought to cause fewer inflammatory reactions than mineral oil or paraffin. Whether that is actually true in practice is debatable, given how many severe complications have been reported with synthol specifically. The lidocaine and alcohol components are functional additions, not safety features. Lidocaine numbs the injection site so the user can tolerate repeated injections. Alcohol reduces but does not eliminate the risk of infection. Neither ingredient addresses the core problem, which is that you are injecting a large volume of non-absorbable oil into living tissue and hoping the body tolerates it. The evidence suggests that hope is not well founded.

1
PubMed Central. The usage of synthol in the body building
2
PubMed Central. Oil injection for cosmetic enhancement of the upper extremities: a case report and review of literature
3
SAGE Journals (Journal of Health Psychology). Bodybuilders’ accounts of synthol use: The construction of lay expertise online
4
PubMed Central. Painful muscle fibrosis following synthol injections in a bodybuilder: a case report
5
Revista Brasileira de Medicina do Esporte. Cosmetic doping: the problems of intramuscular application of oils
6
PubMed Central. Management of Synthol-induced Fibrosis
7
PubMed. Irreversible muscle damage in bodybuilding due to long-term intramuscular oil injection
8
Indian Journal of Pharmaceutical Sciences. Cosmetic Abuse of Site Enhancement Oils: An Insight Review on Synthol and Other Targeted Enhancement Oils
9
Rev. Bras. Cir. Plást.. Complications in sefel-injection of chemicals to increase muscle
10
Taylor & Francis Online / Informa Healthcare (Clin Toxicol). An overview on performance and image enhancing drugs (PIEDs) confiscated in Italy in the period 2017-2019