Synthol is an injectable oil mixture that some bodybuilders inject directly into their muscles to make them appear larger. It contains no anabolic compounds and builds no actual muscle tissue. Instead, it sits inside the muscle like a liquid implant, stretching the surrounding tissue outward to create the illusion of size. The practice carries serious medical risks, from permanent muscle destruction to life-threatening systemic complications, yet synthol remains legal and widely available online.
What Is in It
The standard synthol formula is roughly 85 percent oil, 7.5 percent lidocaine (a local anesthetic), and 7.5 percent benzyl alcohol. The oil component typically consists of medium-chain triglycerides, chosen because they spread relatively evenly through muscle tissue and produce a smoother appearance than longer-chain oils would.1PubMed. The usage of synthol in the body building The lidocaine numbs the injection site so the user can tolerate repeated shots into the same muscle, and the benzyl alcohol acts as a sterilizing agent within the mixture itself.
Not everyone uses the branded product. Some bodybuilders inject plain sesame oil, walnut oil, or paraffin oil without the lidocaine or alcohol components. A scoping review of self-injection case reports found that “Synthol” was named in sixteen of twenty-seven studies on oil-based muscle enhancement, while paraffin oil appeared in ten.2ScienceDirect. “A slippery slope”: a scoping review of the self-injection of unlicensed oils and fillers as body enhancement The health consequences are broadly similar regardless of which oil is used, though paraffin oil has been particularly associated with granuloma formation and calcium metabolism problems.
Where It Came From
The idea of injecting substances locally to inflate muscles goes back to the 1960s, when an Italian product called Esiclene (formebolone) was manufactured for therapeutic use. By the 1980s, European and American bodybuilders had adopted it as a pre-competition trick. Esiclene was a steroid with weak anabolic effects but strong inflammatory properties. The inflammation swelled the muscle temporarily, giving it a fuller look on stage. When Esiclene was discontinued, synthol appeared in the 1990s, created by a bodybuilder looking for a replacement.3Revista Brasileira de Medicina do Esporte. Cosmetic doping: the problems of intramuscular application of oils Unlike Esiclene, synthol does not work through inflammation. It works by physically occupying space inside the muscle belly, functioning as a semi-permanent implant.
The product was originally marketed as “posing oil,” a label that persists today and gives sellers a thin veneer of plausibility. The implication is that it is meant to be rubbed on the skin for a glossy stage look. In reality, it is sold with the understanding that buyers will inject it.
What It Does Inside the Muscle
Once injected, the oil does not get absorbed quickly. The body treats it as a foreign substance and walls it off with connective tissue. Over time, repeated injections create a layered deposit of oil pockets surrounded by scar tissue. This is not muscle growth in any functional sense. The muscle fibers themselves do not enlarge or strengthen. They get displaced and compressed by the expanding oil deposits.
Biopsies of synthol-injected muscles show a distinctive pattern. The connective tissue becomes infiltrated with inflammatory cells, dominated by macrophages (the immune cells that swallow foreign material) along with multinucleated giant cells and lymphocytes.4PubMed Central. Painful muscle fibrosis following synthol injections in a bodybuilder: a case report The giant cells are the body’s attempt to digest something it cannot break down. When the oil resists digestion, the immune response becomes chronic, gradually replacing functional muscle with dense fibrous tissue. This fibrosis is what makes the damage so hard to reverse.
The oil can persist in the body for years. Estimates range from three to five years before the body substantially reabsorbs the material, and even then the scar tissue and structural damage remain long after the oil itself is gone.
Local Complications
The most common problems are the ones injectors can see and feel: painful lumps, redness, skin discoloration, and a hard, unnatural texture to the muscle. But the damage beneath the surface is far worse than what shows externally.
One well-documented case involved a 40-year-old semi-professional bodybuilder who had injected sterilized sesame seed oil into numerous intramuscular sites daily for eight years. By the time he sought medical help, he had a systemic infection and painful swelling in his right upper arm that prevented him from lifting weights at all. Whole-body MRI revealed more than 100 intramuscular oil cysts and complete loss of normal muscle anatomy in the affected areas. When surgeons opened his right upper arm, they found pus-filled cystic scar tissue with almost no normal muscle remaining. A follow-up MRI a year later showed no meaningful muscle regeneration, and the patient was still in pain and unable to train normally three years after surgery.5PubMed. Irreversible muscle damage in bodybuilding due to long-term intramuscular oil injection
That case is extreme in its duration but not unusual in its outcome. The pattern across published reports is consistent: once injections have gone on long enough to produce widespread cysts and fibrosis, the original muscle tissue is essentially destroyed. “Irreversible muscle mutilation” is the phrase the researchers used, and it is not hyperbole. The muscle does not come back.
Risks That Spread Beyond the Injection Site
The dangers of synthol are not confined to the muscles where it is injected. Oil can migrate through the bloodstream and reach distant organs, particularly the lungs. Pulmonary complications from soft-tissue fillers are thought to result from the injected material entering the blood, either because of high tissue pressure at the injection site, accidental puncture of a blood vessel during injection, or massage of the area afterward.6Annals of Medicine and Surgery. Synthol systemic complications: Hypercalcemia and pulmonary granulomatosis. A case report When oil droplets reach the lungs, they can trigger granulomatous inflammation there, producing breathing difficulties and, in severe cases, respiratory failure.
Another systemic complication is hypercalcemia, an abnormally high level of calcium in the blood. A study of 88 men who had injected paraffin or synthol oil into skeletal muscles found that foreign body granulomas formed at injection sites, and macrophages within those granulomas produced high levels of active vitamin D, which in turn drove calcium levels up.7Journal of Bone and Mineral Research. Hypercalcemia After Cosmetic Oil Injections: Unraveling Etiology, Pathogenesis, and Severity Hypercalcemia can cause kidney stones, bone pain, confusion, heart rhythm problems, and kidney damage. The fact that this complication appeared in a cohort of 88 people, not just a single case report, suggests it is not a rare fluke but a predictable consequence of large-volume oil injection.
How Doctors Find and Treat It
Diagnosis often starts when a patient shows up with painful, swollen limbs and eventually admits to oil injections, though not everyone volunteers that history right away. MRI is the key imaging tool. Injected muscles typically appear swollen with scattered intramuscular oil cysts and diffuse signal changes. When inflammatory complications are present, contrast-enhanced sequences show uneven enhancement throughout the affected tissue.8Radiopaedia. Synthol injection in a bodybuilder The MRI pattern is distinctive enough that experienced radiologists can recognize it, though it may initially be confused with soft-tissue tumors or abscesses if the clinical history is not clear.
Treatment, when complications demand it, is surgical. There is no drug that dissolves the oil or reverses the fibrosis. Surgeons must excise the fibrotic tissue, which requires balancing how much to remove against the need to preserve whatever healthy muscle and surrounding structures remain. The procedure can involve significant blood loss, and outcomes depend heavily on how extensively the oil has spread.9PubMed Central. Management of Synthol-induced Fibrosis In milder cases, removing the damaged tissue and managing infection can restore a reasonable appearance and some function. In severe cases like the bodybuilder with more than 100 cysts, normal muscle function is permanently lost even after surgery.
Some patients need multiple operations. If infected tissue is not completely removed, reinfection is common, and the chronic inflammatory state that oil deposits create makes healing slower and less predictable than it would be for a typical surgical wound.
Why People Use It Anyway
Given how dangerous synthol is, the obvious question is why anyone injects it in the first place. The motivations overlap with the broader psychology of image and performance-enhancing drug use. A systematic review of IPED use in the general population found that motivation is typically grounded in appearance, the pursuit of health and youth, and body image disturbance.10PubMed. The injecting use of image and performance-enhancing drugs (IPED) in the general population: a systematic review For synthol users specifically, the appeal is instant visual results without years of training. Anabolic steroids accelerate real muscle growth but still require heavy lifting and diet discipline. Synthol skips all of that. You inject and you look bigger the same day.
The psychological profile of heavy synthol users often includes features of muscle dysmorphia, a condition in which a person perceives their body as much smaller or less muscular than it actually is. Someone with muscle dysmorphia may look objectively large to everyone around them but still see a small, inadequate body in the mirror. For these individuals, the risk calculation is different than it would be for someone with a more typical body image. The perceived need for size feels urgent enough to override warnings about cysts and infections.
Online communities play a significant role. Synthol use is discussed openly on bodybuilding forums, where experienced users share injection protocols, recommended volumes, and cycling schedules. Researchers studying these communities have noted that users construct a form of “lay expertise,” drawing on personal experience and community knowledge to develop what sounds like medical guidance.11PubMed Central. Bodybuilders’ accounts of synthol use: The construction of lay expertise online The advice can be detailed and confident, but it has no clinical oversight. A forum post recommending specific volumes per muscle group carries the same authority as any other internet comment, regardless of how many replies agree with it.
Legal Status and Why It Stays Available
Synthol is not a controlled substance in most countries. It is not classified as a drug, a steroid, or a medical device. Because its ingredients are individually unremarkable (cooking oil, a common anesthetic, and an alcohol used in food preservation), there is no obvious regulatory category it falls into. It is sold openly online, often under the “posing oil” label, and a simple search returns dozens of vendors.
This legal gray area frustrates public health professionals but is difficult to resolve. Banning the sale of medium-chain triglyceride oil would affect legitimate food and cosmetic industries. Banning lidocaine would disrupt medical practice. The combination of the two in a bottle marketed for topical use is hard to prohibit without specific legislation targeting injectable cosmetic oils, which few jurisdictions have pursued.
Competition organizations have taken their own stance. Most professional bodybuilding federations ban synthol and other site-enhancement oils, and judges are trained to spot the telltale signs: muscles that look round and puffy rather than striated, unnatural proportions where a small muscle group suddenly matches or exceeds much larger ones, and a “balloon-like” quality to the skin surface. Competitors caught using synthol face disqualification, though enforcement depends on how obvious the results are. Subtle use is harder to detect visually than the extreme cases that go viral online.
The Difference Between Synthol and Steroids
People sometimes lump synthol in with anabolic steroids, but they work through completely different mechanisms and the comparison is misleading. Steroids are hormones that bind to receptors inside muscle cells, increasing protein synthesis and causing the muscle fibers themselves to grow. The resulting muscle is real, functional tissue. Steroid use carries its own well-documented health risks, from liver damage to cardiovascular problems, but the muscle gains are genuine and the user gets stronger.
Synthol does none of this. It adds volume without adding any contractile tissue. A synthol-enhanced bicep may measure several inches larger, but it is not stronger. In fact, it is often weaker, because the oil displaces and compresses the actual muscle fibers. The contrast is stark when synthol users attempt to demonstrate strength. Videos circulate online of individuals with enormous-looking arms who struggle to curl modest weights, precisely because the size is oil, not muscle.
This distinction matters for understanding the health risks too. Steroid side effects are primarily hormonal and metabolic. Synthol side effects are primarily structural and inflammatory. A steroid user who stops taking steroids will gradually lose the extra muscle mass but retains a functioning body. A long-term synthol user who stops injecting is left with oil deposits, scar tissue, and potentially destroyed muscle that does not regenerate.
What MRI Reveals About Long-Term Damage
Imaging studies have given doctors an unusually clear picture of what happens inside synthol-injected limbs. Normal muscle on MRI has a characteristic striped appearance, with fibers running in organized parallel bundles. In heavily injected muscles, that architecture is gone. Instead, MRI shows swollen tissue shot through with scattered cysts of varying size, each representing a pocket of trapped oil.12PubMed. Irreversible muscle damage in bodybuilding due to long-term intramuscular oil injection The cysts are intramuscular rather than subcutaneous, meaning they sit deep inside the muscle belly rather than just under the skin.
In the case of the bodybuilder with eight years of daily injections, whole-body MRI mapped out the full extent of the problem across multiple muscle groups. The sheer number of cysts, over 100, gave a sense of scale that physical examination alone could not. Follow-up imaging a year after surgery showed that the body had not filled in the gaps with new muscle. The spaces left by removed cysts and scar tissue remained as they were. This finding is what makes the damage so concerning from a rehabilitation standpoint. Muscle tissue has some regenerative capacity, but when the architecture is disrupted this thoroughly, there is nothing left to regenerate from.
Harm Reduction in an Unregulated Space
Public health researchers who study image and performance-enhancing drug use generally recognize that moralizing does not stop people from injecting. The question then becomes whether there are ways to reduce the harm for those who are going to do it regardless. For most injectable IPEDs like steroids, harm reduction involves needle exchange programs, sterile injection advice, and access to health monitoring. Synthol presents a harder problem because the substance itself, not just the route of administration, causes the damage. Sterile technique and clean needles do not prevent oil cyst formation or fibrosis. They reduce infection risk, which is one real component of synthol harm, but the core problem of foreign material sitting permanently in muscle tissue is inherent to the practice.
Some clinicians have argued for better education targeted at gym communities, focusing not on abstract health warnings but on the specific, visible outcomes that synthol users care about. The fact that long-term synthol use destroys functional muscle and eventually makes a person weaker, not just sick, may be more persuasive to someone motivated by appearance and performance than warnings about granulomas and hypercalcemia. Showing MRI images of cyst-riddled muscle tissue alongside photos of what those arms look like years later, when the inflammatory process has run its course, may be more effective than listing complications in clinical language.
For people already experiencing symptoms from past synthol use, the barrier to seeking help is often shame. Many users delay medical attention because they do not want to admit what they have done, particularly to a healthcare provider they expect will judge them. Creating clinical environments where disclosure is met with pragmatic medical care rather than lectures is one of the more actionable steps the medical community can take. The damage is often already done by the time someone walks through the door. What matters at that point is accurate diagnosis, appropriate imaging, and surgical planning that preserves as much function as possible.