The unknowns cannot be turned into reassurance.

The missing safety record

The FDA review checked September 30, 2026 found no human safety studies of TB-500. It also found no animal studies covering short-term toxicity, repeated use, pregnancy, gene damage or cancer.

Toxicity means the harm a substance can cause. Without the studies, TB-500’s side effects and their frequency cannot be described as a known pattern.

The concern the FDA names

The FDA is concerned that injected TB-500 could trigger an immune response, meaning the body’s defence system reacts to it. Clumps or unwanted material left in a batch may heighten that concern.

The agency describes possible immune reactions ranging from no visible symptoms to life-threatening reactions. This is a risk assessment, not a measured rate of reactions to TB-500 in people.

A test sheet is not the whole answer

The FDA found gaps in a representative TB-500 test sheet. It lacked checks for bacterial poisons, clumps and a full assessment of unwanted material. A French laboratory that tests products used in horse racing checked items sold online under the TB-500 name. Their contents did not always match the descriptions.

A purity claim cannot fill the missing human safety record. Ask what was tested and what was left untested.

Do not borrow another substance’s record

Short studies of full-length thymosin beta-4 do not establish the safety of TB-500. They concern a different substance and different uses.