Can fillers be used for buttock enlargement?

Body filler is sometimes offered as a simple fix, and that is the worry behind this question. If you are in Mamaroneck, Larchmont or anywhere in Westchester and have seen it offered, start with what the regulator says.
The direct answer
The U.S. Food and Drug Administration warns against it in its consumer update: "Using injectable filler for large-scale body contouring or body enhancement can lead to serious injury, including long-term pain, infection, permanent scarring or disfigurement, and even death."
Buttock enlargement is a form of body enhancement, which is the use that statement describes. The full list of dermal filler do's and don'ts is on the same page.
What the FDA statement lists
The injuries named are long-term pain, infection, permanent scarring or disfigurement, and death. None of them is a minor side effect.
The agency has separately addressed illegal use of injectable silicone for body contouring and the health risks that come with it.
What you can do now
Before any body treatment, ask the person offering it what product is being injected and where it was obtained. If you cannot get a clear answer, decline.
If you have already had body filler elsewhere and you have pain, signs of infection or a change in the skin, contact a clinician promptly. Do not wait to see whether it settles.
What to leave alone
Do not accept a cash-only, at-home or pop-up offer for body contouring. Do not treat a bargain price as a sign that a product is safe.
The question that comes next
People often follow up by asking what fillers are meant for. Bring that question to your clinician at a consultation.