Field guide · Entry 04 of 06 Psilocybe semilanceata
What is in a liberty cap, and how much it varies
Psilocybin, psilocin and baeocystin in Psilocybe semilanceata, how much the measured content varies, and the acute effects and risks on record.
The liberty cap contains psilocybin as its main active compound, together with smaller amounts of baeocystin and usually only traces of psilocin. Measured psilocybin contents range from a fraction of a percent to more than two percent of the dried weight, depending on the collection. That range is the main chemical fact a reader needs: a wild mushroom has no label, and two collections can differ several times over.
The compounds
| Compound | What it is | In the liberty cap |
|---|---|---|
| Psilocybin | A tryptamine with a phosphate group; the stored form | The main compound, typically around 1 percent of dry weight |
| Psilocin | Psilocybin without the phosphate; the form that acts in the brain | Usually only traces in the mushroom itself |
| Baeocystin | A close relative of psilocybin with one methyl group fewer | Present, in some studies at a relatively high level |
Psilocybin is converted into psilocin in the body, and psilocin is the compound that produces the effects. The same conversion happens in a damaged mushroom, where it is the first step towards the blue staining described in the field characters entry (Lenz et al. 2020).
Measured contents
The first chemical confirmation came in 1963, when Albert Hofmann analysed liberty caps collected in Switzerland and France by the botanist Roger Heim and found about 0.25 percent psilocybin by dry weight. It was the first report of psilocybin in a European mushroom. Later work with better methods found higher and more variable figures.
| Study | Material | Psilocybin, % of dry weight |
|---|---|---|
| Jokiranta et al. 1984 | Collections from across Finland | 0.62 to 2.37, mean 1.42 |
| Beug and Bigwood 1982 | Pacific Northwest, USA | about 0.6 to 1.3, mean about 1.0 |
| Hofmann et al. 1963 | Switzerland and France | about 0.25 |
The Finnish samples contained psilocin at only 0.01 to 0.02 percent. Stijve and Kuyper, analysing more than a hundred European species, also found baeocystin in the liberty cap (Stijve and Kuyper 1985). Beug and Bigwood noted that across the species they tested, the content varied by more than a factor of seven from one collection to the next.
Psilocybin is also fairly stable once the mushroom is dried. A Finnish study detected it in herbarium specimens more than a century old (Ohenoja et al. 1987).
What the variation means
Wild liberty caps differ in size, water content and chemistry. A small dry cap and a large wet one weigh very different amounts for the same chemistry, and the measured psilocybin content of collections differs several-fold. Nobody picking a mushroom can know what it contains. Add to that the possibility that one cap in a handful is a lookalike, and the chemical uncertainty becomes a safety problem.
Acute effects on record
The UK's drug information service FRANK describes the effects of magic mushrooms as starting after 30 minutes or more and lasting up to about five hours. People may become giggly and excited, or confused, paranoid, anxious and overwhelmed; nausea, vomiting and distortions of sound and vision are common (FRANK).
Medical case reports describe what can go wrong after eating liberty caps specifically:
- Britain, 1978. Three patients presented with states ranging from a typical psychedelic experience to transient psychosis and a longer schizophrenia-like illness; two showed signs of an overactive sympathetic nervous system (Hyde et al. 1978).
- Kraków, 2004. Four young people were admitted to a toxicology department after eating liberty caps; one developed a psychosis and stayed several days. Their main source of information had been the internet (Satora et al. 2005).
- Poland, 1998. An 18-year-old developed a heart rhythm disorder and a heart attack after eating liberty caps (Borowiak et al. 1998).
- Aberdeen, 2022. Doctors reported takotsubo cardiomyopathy, a sudden weakening of the heart muscle, after recreational use of liberty caps (Kotts et al. 2022).
These are individual case reports, and serious outcomes are uncommon. They show that the risks are not limited to poisoning by the wrong species.
This site gives no dosage information for wild mushrooms. The psilocybin content of a wild collection cannot be known, the identification cannot be confirmed without an expert, and in the UK and the Netherlands possessing picked liberty caps is an offence.
What to read next
The law entry explains how the UK and the Netherlands came to list the fresh mushroom itself. The history entry covers the 1799 London poisoning and the scientific work that followed.