Short version: some of them, a little, for some things, if you buy a real one and keep your expectations sensible. That is less exciting than the marketing, and closer to the truth than either the "ancient miracle cure" crowd or the "it's all a scam" crowd will tell you.
This is the reality check behind it all. For what each mushroom is, start with functional mushrooms, explained; for why so many products can't work at all, see the quality guide.
Why the evidence is messy
Before the mushroom-by-mushroom rundown, it helps to know why nobody can hand you a clean yes or no.
Most human studies are small, short, and sometimes funded by the company selling the product. Lab and animal results, which are often spectacular, do not reliably carry over to people.
On top of that, there is a gap between what gets studied and what you can buy: trials tend to use specific, standardized extracts at doses often higher than a typical capsule, while a large share of shelf products are mycelium grown on grain, which is mostly starch and carries little active compound.
Many supplements never reach the dose of beta-glucans or triterpenes the research suggests you would need. And because supplements are not regulated like drugs in the US, the FDA does not check them for effectiveness before they go on sale.
So "does it work" is really two questions stacked together: does the compound do anything, and did you actually buy the compound. The quality guide is about the second one.
What the research shows, mushroom by mushroom
Lion's mane
The most interesting brain story, and still an unfinished one. A small, often-cited 2009 Japanese trial in older adults with mild cognitive impairment found their scores improved while they took it, then slid back after they stopped.
Later small studies have hinted at benefits for mood, anxiety, and sleep, while at least one trial in healthy young students found nothing at all. The trials are small and short, so this is promising rather than proven.
What keeps researchers interested is the mechanism: lion's mane compounds appear to stimulate nerve growth factor, a plausible reason it might support the brain. Worth a try for focus or mood with realistic hopes, not a nootropic guarantee. (Lion's mane guide.)
Reishi
The calm-and-immune mushroom, with some evidence. The best summary is a 2016 Cochrane review of cancer patients, which found that reishi taken alongside standard treatment gave a small boost to immune-cell activity and quality of life, but no improvement in survival, and rated the underlying trials low quality.
Small studies suggest it may ease cancer-related fatigue and improve sleep. Its long reputation for calm and better sleep is more traditional than proven.
A recurring catch is dose: many reishi products are underdosed and skip the alcohol extraction that pulls out the triterpenes. A reasonable bet for winding down and general support, not a treatment. (Reishi guide.)
Cordyceps
The energy mushroom. Several small trials point to modest gains in aerobic capacity and time to exhaustion, but often using a blend rather than cordyceps alone, frequently in older or recreational subjects rather than trained athletes, and with mixed results at the elite level.
One of the most-cited exercise studies was funded by the company that made the product. The fair read is a possible, gentle edge in stamina or daily energy for some people, without the spike and crash of caffeine, not a guaranteed performance boost. (Cordyceps guide.)
Turkey tail
The most researched of the bunch, with a big asterisk. Its compounds PSK and PSP have the strongest clinical record here, but as a supervised add-on to chemotherapy, not as a supplement you take on your own.
PSK has been an approved adjunct cancer therapy in Japan for decades, and a 2014 trial showed it acts as a prebiotic that feeds gut bacteria.
That is real, and it is also not a claim about a bottle of capsules used for everyday wellness. For the ordinary buyer, the fair expectation is general immune and gut support. (Turkey tail guide.)
Chaga
The antioxidant mushroom, and the one with the thinnest human evidence. Chaga scores very high on antioxidant lab measures, and there is promising laboratory and animal work on immunity, inflammation, and blood sugar.
What is missing is good human trials, so most of the confident claims you will read run ahead of the data. Treat it as a reasonable daily antioxidant baseline rather than a proven remedy, and mind the safety cautions, since chaga carries more of them than the others. (Chaga guide.)
What "working" actually looks like
If you are picturing a pill you feel kick in, reset that. When functional mushrooms help, it tends to be subtle and cumulative: a baseline shift you notice over two to three weeks of steady use, not a hit you feel an hour later.
Effects vary a lot from person to person, some people notice nothing, and none of this replaces sleep, food, exercise, or medical care.
The people most likely to be let down are the ones expecting a drug. The people most likely to be quietly pleased are the ones who bought a tested, fruiting-body extract, took it daily for a month, and treated it as a small support rather than a cure.
When to talk to a doctor
These are not harmless just because they are natural. Several can interact with medication, including blood thinners, diabetes drugs, and immune-suppressing medication, and a few stimulate the immune system in ways that matter if you have an autoimmune condition.
Check with your doctor or pharmacist before starting if you are pregnant, nursing, on medication, or managing a health condition, and never use a mushroom supplement in place of treatment your doctor has prescribed.
Bottom line
Do functional mushrooms work? For some people, modestly, for some things. The evidence ranges from genuinely interesting, like turkey tail's immune research and lion's mane's effect on the brain, to thin, like chaga in humans.
Almost all of it comes with the caveat that the product has to be real to stand a chance. Buy quality, give it a few steady weeks, and judge it as a gentle support, not a miracle.
To make sure your bottle can even deliver, run it through the quality checks, then pick a starting point with the lion's mane, reishi, cordyceps, turkey tail, or chaga guides.
