First, what compounding means
With compounding, a medicine is made or mixed for a particular order instead of supplied as a ready-made drug product.
This page begins with pharmacies that fill a prescription by making medicine for one named patient. Their part of US law is called section 503A.
A licensed pharmacy still has to meet the rules for the raw ingredient it uses.
Compounded medicines lack FDA approval as of September 26, 2026. The FDA is the US medicine regulator.
The agency does not check their benefit, safety or quality before they are sold.
The request was taken back; the rules still apply
On the FDA page marked April 22, 2026, thymosin alpha-1 is listed among ingredients that people had asked it to allow for making medicines. Those people took back their request; the agency still lists its safety concerns.
The FDA gives no date for when that request was taken back. The pharmacy still has to meet the same ingredient rules.
As of September 28, 2026, this ingredient is missing from the allowed list for pharmacies making medicine for a named patient's prescription.
The FDA found no published quality standard for this ingredient: a written description of the ingredient and the tests used to check its quality. It also found no approved medicine containing it.
Together, those findings mean a pharmacy cannot legally make it from the raw ingredient for a named patient's prescription.
FDA record of requests taken back FDA ingredient list for these pharmacies
A panel vote is advice
The FDA panel checked two ingredient forms: thymosin alpha-1 itself, called the free base, and thymosin alpha-1 acetate, its salt form. In December 2024, the vote on each was 17 against and 4 in favour of adding it to the allowed list.
A panel vote does not change the law; changing the list requires a formal FDA rule.
As of September 28, 2026, no final FDA rule on this ingredient had been published.
FDA's final meeting minutes FDA explanation of the list process
A larger supplier still needs a separate check
Some larger suppliers make batches of medicine for clinics and hospitals. They work under a different part of US law, called section 503B.
As of September 28, 2026, the FDA listed thymosin alpha-1 under those rules among ingredients with too little information for it to judge. That group is not covered by the agency's temporary policy of holding off on action against businesses using those ingredients.
FDA ingredient list for larger suppliers FDA explanation of larger suppliers