Sterites

Sterites (Steroid + Nanite) are strength-enhancing nanites. They are injected into the heart, where they travel through the bloodstream and are absorbed into the muscle cells. There, they replicate and form artificial contractile fibers, in turn enhancing physical strength. They last a few hours before they lose cohesion and disintegrate.

Sterites are banned on most worlds due to alarming health concerns and the potential for abuse, misuse and tampering, most famously leading to the death of Psychballer Jacob Humphres.

Health Concerns
Sterites are comprised mostly of silicon and carbon. Though they are designed to disintegrate slowly so that the body can remove their waste products, this occasionally fails and users suffer toxic effects.

On at least nineteen recorded cases during clinical trials, Serite users suffered excessive strength enhancement, which resulted in the jacked-up muscles tearing the tendons away from the bones. Loudly and painfully.

Prolonged use of Sterites can lead to heart damage (as the heart also absorbs them from the initial injection), liver damage, kidney damage and blindness. They're also known to cause sterility, but it could be the result of poor manufacturing.

Some users suffered faulty Sterites that did not stop replicating. These users eventually ended up ripping themselves apart, or suffering catastrophic muscle failure.