Why algorithmic stablecoins are risky: the lesson of UST
A lot of the fear beginners have about stablecoins traces back to one name — UST. The algorithmic stablecoin that crashed from a dollar to a few cents in days in 2022 and wiped out countless people. What actually went wrong, and how could something carrying the word "stablecoin" collapse this completely?
Here's a conclusion you can just remember: algorithmic stablecoins are dangerous because they have no equivalent real assets underneath — they prop up a dollar entirely with an algorithm. In calm markets it looks clever, but once confidence collapses, that algorithm not only fails to save it, it accelerates the fall — this is the "death spiral." Fiat-backed coins like USDT and USDC have cash and Treasuries behind them, so the worst case is a discount, rarely zero. That's the fundamental dividing line. Below, in plain terms: the mechanism, how UST collapsed, and how to spot an algorithmic stablecoin at a glance.
How an algorithmic stablecoin "holds a dollar"
A fiat-backed stablecoin's logic is plain: issue one coin, hold one coin's worth of money. Algorithmic stablecoins try to skip that step — instead of real assets, they use a set of rules that auto-adjust supply and demand so the price snaps back to a dollar on its own.
The classic approach is the "two-token model," using another freely mintable "governance token" as an adjustment valve. Take UST: it was paired with LUNA, and the rules ran roughly like this:
- The system always allows "1 UST swapped for a dollar's worth of LUNA," and vice versa.
- When UST falls below a dollar, arbitrageurs swap cheap UST for a dollar's worth of LUNA and pocket the difference — a process that burns UST and mints LUNA, in theory shrinking UST supply and pushing the price back to a dollar.
- The reverse: when UST rises above a dollar, burn LUNA and mint UST to push the price down.
See the problem? Its "reserve" is actually another coin that swings in value and can be minted without limit. When the market is good and confidence is high, the mechanism turns smoothly; but it has one fatal precondition — LUNA has to stay valuable. The moment that precondition breaks, the whole mechanism turns on itself.
A blunter analogy: a fiat-backed stablecoin is like "you deposited $100 in cash, then issued a $100 IOU" — the IOU can always be cashed for real money; an algorithmic stablecoin is like "I print an IOU, and at the same time print another slip signed by myself as the collateral." While the slip is valuable it looks watertight; the moment no one believes the slip, both pieces of paper become waste together. It builds "stability" on top of something unstable — at heart it's using confidence to plug a hole in assets. While confidence lasts, it lasts; when confidence breaks, it breaks faster than anything.
If it's this risky, why did people buy it
If algorithmic stablecoins are this fragile, why did so many people pile in back then? Because it usually came with an extremely tempting bait: an absurdly high yield. Before UST collapsed, its surrounding ecosystem long offered double-digit annualised "deposit yields" — offering that kind of return on a coin billed as "stable" is a huge draw for people who don't know better.
But that's exactly the crux — a stablecoin doesn't earn interest by itself, so high yield conjured out of thin air must come from somewhere else. Either it's subsidising old users with a stream of new money (a Ponzi structure), or it's putting the funds into high-risk uses. Either way, it's built on a sandcastle of "scale keeps growing, confidence keeps holding." The moment growth stalls and panic appears, the yield can't hold and the price can't hold — both cave in together. So when you see "stablecoin + very high interest," the right reaction isn't excitement, it's alertness: that's not a free lunch, it's a price tag — marking how dangerous the coin is.
Something that claims to be "stable and principal-protected" while also handing you returns far above normal — in finance those two things usually can't both be true at once. When they're sold together, assume "stable" and "principal-protected" are the false parts, and you'll usually be closer to the truth.
The UST death spiral, step by step
In May 2022, UST demonstrated in the most brutal way what happens when that precondition breaks. Break the process into steps and you'll understand what "death spiral" means:
- Large sell-offs ignite panic: a lot of UST is dumped in a short window, the price starts to fall below a dollar. The market begins to doubt "it can't hold."
- The algorithm kicks in, frantically minting LUNA: by the rules, to let people swap UST for a dollar's worth of LUNA and thus burn UST, the system mints huge amounts of LUNA.
- LUNA is diluted, its price crashes: LUNA supply spikes instantly, and with panic selling on top, the price falls off a cliff.
- Saving it makes it worse: the more LUNA falls, the more of it must be minted to redeem the same value, crushing LUNA's price further; as LUNA fails, UST has even less underneath it and falls harder.
- Spiral to the bottom: within days, UST fell from a dollar to a few cents and LUNA went from its highs to nearly zero.
That's the horror of the death spiral: the mechanism meant to save the stablecoin becomes the accelerator that crushes it. When a fiat-backed stablecoin depegs, there's at least cash and Treasuries underneath to draw arbitrageurs back in to buy; UST's "floor" was a coin going to zero — effectively no floor. To see where the UST depeg sits in the whole history of stablecoin incidents, see what a stablecoin depeg is.
After UST collapsed, new algorithmic or semi-algorithmic stablecoins kept appearing, claiming "the mechanism's improved, this one won't crash." Historically, very few of those promises held. For a beginner, the safest assumption is: the death spiral risk of algorithmic stablecoins is structural, and tweaks can't fix the essence.
The fundamental difference from fiat-backed
Put the two side by side and the difference is obvious:
| Comparison | Algorithmic (e.g. UST) | Fiat-backed (e.g. USDT, USDC) |
|---|---|---|
| What's behind it | An algorithm + a coin that swings and can be minted | Real assets like cash and short-term Treasuries, about 1:1 |
| Floor during a depeg | Almost none; saving it worsens it | Real assets, drawing arbitrage back to the peg |
| Worst outcome | Death spiral, possibly zero | A brief discount, usually repegs |
| Right for beginners? | No, stay away | Yes, the correct beginner choice |
In one line: a fiat-backed coin's risk is "are the assets enough," an algorithmic coin's risk is "will the mechanism self-destruct." The former may take a discount, the latter may go to zero. That's why we keep stressing that beginners only touch mainstream stablecoins with real assets behind them. For the stablecoin types and their mechanisms, see what a stablecoin is.
One more difference worth calling out on its own: whether a coin can "come back" after a depeg is a completely different fate for the two. When a fiat-backed coin depegs, there are real assets underneath, so as long as redemption stays open, arbitrageurs come in to buy the cheap coin, redeem at a dollar, and pull the price back to the peg — that's how USDT's brief depegs and USDC's drop to $0.87 repegged. When an algorithmic coin depegs, its "floor" is a coin going to zero, so arbitrageurs have no profit to chase and no way in, and the price loses its automatic pull back and just grinds lower. One is "dip and snap back," the other is "once it falls, it doesn't return" — the dividing line a beginner most needs to remember.
How to spot an algorithmic stablecoin at a glance
You don't need to read the whitepaper; just look at how it describes "why it's worth a dollar." These phrasings should raise your guard:
- Emphasising "adjusting supply and demand by algorithm," "no collateral needed," or "under-collateralised," rather than "1:1 cash and Treasury reserves."
- Mentioning "minting / burning against a governance token" to hold the peg.
- Coming with an absurdly high yield promise — like a double-digit annualised "stablecoin deposit." That's practically standard kit for algorithmic schemes and Ponzi structures.
By contrast, a proper fiat-backed stablecoin will state plainly "we hold about a dollar of cash and short-term Treasuries for every coin," and can produce periodic reserve reports. To verify a stablecoin's reserves and audit sources, use the issuer / audit lookup; for the general concept of stablecoins, an authoritative encyclopedia entry is the Stablecoin article on Wikipedia.
Watch out for a "grey area" type: partly algorithmic, semi-collateralised. These say they "also have some real collateral" to sound a bit steadier than pure algorithmic. But as long as their stability mechanism still relies on "a coin that swings and can be minted" as the backstop, that partial collateral often can't hold in a real panic — UST also tried to bring in external reserves late in the game, and it still didn't stop the death spiral. So don't be fooled by "there's some collateral"; the key is whether the core of how it holds the peg depends on something that can go to zero. If it does, the risk is structural.
Finally, the simplest rule of action for a beginner: you don't need to study which algorithmic stablecoin "might be fine." There are plenty of mainstream options — USDT, USDC, FDUSD — with real assets behind them and everything you need, so there's no reason to walk the algorithmic minefield for a bit of gimmick. Dropping "algorithmic stablecoin" straight into your blacklist is the highest return-on-effort self-protection there is.
Any stablecoin whose peg mechanism you can't understand and that promises high yield — don't touch it, period. Use only mainstream stablecoins with real assets behind them, like USDT, USDC and FDUSD, and you've already sidestepped most "goes-to-zero" risk.
The lesson of UST isn't "all stablecoins are dangerous," it's "there's a class of stablecoin with a fuse to zero built into its design." Tell apart algorithmic and fiat-backed, avoid the former and use only the latter, and you've shut the fiercest stablecoin risk out at the door.
FAQ
Why is an algorithmic stablecoin riskier than USDT?
Because an algorithmic stablecoin has no equivalent real assets behind it; it holds a dollar through an algorithm (usually minting and burning against another coin). Once market confidence collapses, the algorithm actually accelerates the fall, forming a death spiral that can go all the way to zero. Fiat-backed coins like USDT have cash and Treasuries behind them, so the worst case is a discount, not usually zero. That's the fundamental difference.
How did UST collapse?
UST held a dollar by minting and burning against LUNA. After large sell-offs triggered a depeg in May 2022, the algorithm frantically minted more LUNA to save UST, diluting LUNA's price into a crash, which in turn made UST even harder to hold up, forming a death spiral. Within days UST fell from a dollar to a few cents and LUNA went nearly to zero.
How can I spot an algorithmic stablecoin at a glance?
Look at how it holds a dollar. If the pitch talks about "adjusting supply and demand by algorithm," "minting and burning against a governance token," or "no collateral needed / under-collateralised," rather than "1:1 cash and Treasury reserves," it's very likely algorithmic or partly algorithmic. Pair that with an absurdly high yield promise and you can be almost certain to stay away.
Should a beginner touch algorithmic stablecoins?
Not advised. Algorithmic stablecoins are mechanically complex and have collapsed to zero repeatedly in history — the risk is far beyond what a beginner can bear or judge. Beginners should use only fiat-backed stablecoins with real assets behind them, like USDT, USDC and FDUSD, and treat any stablecoin promising high yield as a scam.