Intramuscular injections of oils such as synthol is sometimes used in amateur and professional body-builders to enlarge their muscle volume. What are the long-term side effects of intramuscular oil injection?

What I found so far is limited:

  • (1) gives some ideas but isn't written in English, and I can only access the abstract, so I cannot verify how serious the study is.
  • (2), (3) and (4) are just case report.


Synthol consists usually of oil, benzyl alcohol and lidocain. It consists of 85% of oil (normally it is oil built by medium-length MTC chains because it gives the best effects), 7,5% of lidocain (painkiller), 7,5% of alcohol (to sterilize the mixture). Synthol is a substance used by body builders as a temporary implant which is injected deeply into the muscle. The enlargement effects are immediate. Synthol is used in small groups of muscles to enlarge their volume (for example triceps, biceps, deltoids, muscles of the calf). Some serious drawbacks can be visible while using synthol. The muscles deform and become unnaturally shaped. The side effects of synthol are manifold and they can also cause a damage of nerves, oil embolic of the pulmonary, occlusion of the pulmonary artery, myocardial infarction, cerebral stroke and infectious complications.

This case report describes a 26-year-old body builder who had practiced several months of intramuscular self-injection of walnut oil. Apparently this is a normal procedure amongst body-builders. Our patient complained of swelling and tenderness overlying an injection site. Injections of oil may cause foreign body reactions, leading to tumours named according to the injected material; e.g. paraffinoma, oleoma. Systemic distribution has been reported to result in pulmonary complications.

Introduction: Synthol is a site enhancement oil used by bodybuilders to boost the cosmetic appearance of muscles. Here, we describe the case of a patient with severe side effects following repeated intramuscular injections of synthol in his right biceps muscle.

Case presentation: A 29-year-old Middle Eastern male bodybuilder, following intramuscular injections of synthol five years ago, presented with painful pressure in his right upper arm. On presentation to our clinic, his muscle appeared disfigured. Magnetic resonance imaging revealed scattered cystic fatty lesions in the muscle. The affected part was surgically removed and histopathology showed inflammatory changes with fibrosis and a so-called Swiss cheese pattern.

Conclusion: Synthol injections that are used for the short-term enhancement of muscle appearance by bodybuilders bear the danger of long-term painful muscle fibrosis and disfigurement.

Intramuscular oil injections generating slowly degrading oil-based depots represent a controversial subject in bodybuilding and fitness. However they seem to be commonly reported in a large number of non-medical reports, movies and application protocols for 'site-injections'. Surprisingly the impact of long-term (ab)use on the musculature as well as potential side-effects compromising health and sports ability are lacking in the medical literature. We present the case of a 40 year old male semi-professional bodybuilder with systemic infection and painful reddened swellings of the right upper arm forcing him to discontinue weightlifting. Over the last 8 years he daily self-injected sterilized sesame seed oil at numerous intramuscular locations for the purpose of massive muscle building. Whole body MRI showed more than 100 intramuscular rather than subcutaneous oil cysts and loss of normal muscle anatomy. 2-step septic surgery of the right upper arm revealed pus-filled cystic scar tissue with the near-complete absence of normal muscle. MRI 1 year later revealed the absence of relevant muscle regeneration. Persistent pain and inability to perform normal weight training were evident for at least 3 years post-surgery. This alarming finding indicating irreversible muscle mutilation may hopefully discourage people interested in bodybuilding and fitness from oil-injections. The impact of such chronic tissue stress on other diseases like malignancy remains to be determined.

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