These substances are injected directly into the target muscles, where they stretch muscle fascia. The theory is that as they are broken down by the body over a period of several months, the space left by them is replaced with new muscle tissue growth. Upon injection, roughly 70% of the oil remains in the muscle, while the other 30% is absorbed into the body as lipids. These substances do not inherently contain any androgenic steroids although users of site enhancing oils are of course far more likely to use performance enhancing drugs. As with any non-medically administered injectable, usage carries high risks.
A medical study of synthol injections would agree with that assessment. Even though the bodybuilder injections make arms look like Popeye, this appearance is completely deceiving since such “enhancement oils do not increase muscular strength or performance and are used solely for cosmetic purposes.” Some of the major potential side effects include “oil embolism, myocardial infarction, cerebral stroke, ulcers and infections.” The worst side effect is the cystic fatty lesions that are created within the muscle that resemble a “Swiss cheese pattern.”