LSD purity: why iso-LSD decides how strong a tab is
LSD purity is not the same question as cocaine purity. Cut tabs do not exist. A blotter square is far too small to hold a useful amount of filler, so nobody bothers adding any.
When a tab disappoints there are only five reasons for it. There is nothing on the paper. There is something else on the paper, like NBOMe or DOC. It was underdosed to begin with. It has broken down. Or a large part of what was dropped on it was iso-LSD, which does nothing at all.
What purity means for a tab
For a powder, purity asks about fillers: how much of the gram is drug and how much is something cheaper. For blotter it does not apply. A tab carries about a tenth of a milligram of anything, so a filler has no room to matter and nobody gains by adding one.
The table below takes the five reasons a tab can let you down and gives what a reagent shows for each.
| Reason | What you see |
|---|---|
| Nothing on the paper | No colour |
| Another chemical, NBOMe or DOC | Wrong colour, or none |
| Underdosed from the start | Pale colour |
| Broken down by heat or light | Pale colour |
| Iso-LSD | Normal colour |
Four of the five change what you see. The fifth does not. Iso-LSD is also the only one already decided before the tab reaches you.
The same molecule, built two ways
LSD has one joint in the middle of it that can be put together two ways round. One way works. The other way is iso-LSD, and it does nothing.
Everything else about the two is identical: same atoms, same weight, same response to anything you can do at home. Chemists count four possible versions in total, but two of them never show up in anything sold, so a tab holds LSD, iso-LSD, or more often a mix of the two.
How much of a tab is dead weight
Nearly every tab ever analysed has held both. The split runs from about 10% iso-LSD to about 70%, and where a batch lands depends on who made it. Forensic labs use the ratio to tell one source from another.
Those are seized samples, so they describe other people’s paper and not the tab in your hand. What they show is that the dead version is normal rather than rare, and that the amount swings a long way from batch to batch.
That is the awkward part for anyone deciding a dose. A number written on a tab covers everything dropped on the paper, not how much of it works. The swing between batches is wider than the gap between a 100 and a 150 microgram tab.
Where it comes from, and what you can do about it
Most of the iso-LSD on a tab was already there when you bought it. It forms while the acid is being made, and how much ends up on the paper comes down to how carefully whoever made it finished the job. The change runs both ways, so a careful producer turns it back into LSD instead of throwing it out. A careless one leaves it in, because it still weighs something.
Alkaline things turn LSD into iso-LSD. Soap left on your fingers, bleach, baking soda, a surface wiped with cleaner. That is the one everyday slip that makes the dead version rather than simply wrecking the tab.
Heat, light, damp and air do something else. They break the acid apart into other things entirely, and none of those are iso-LSD. A tab that spent a hot festival weekend in a pocket is weak because some of the LSD is gone, not because it turned into its twin.
So handle blotter with clean dry hands, or with tweezers. Keep it cold, dark, dry and away from anything soapy. And take the iso-LSD share as fixed, because nothing you do at home moves it in your favour.
What it does
Nothing anyone has managed to measure. Albert Hofmann and colleagues gave people up to 500 micrograms of it, about five tabs’ worth of material, and saw no psychedelic effect at all.
So the ratio is simple arithmetic. A tab carrying 150 micrograms, 60% of it iso-LSD, gives you about 60 micrograms of the real thing. The paper weighs the same, a reagent looks the same, and the dose is a little over a third of what the number promised.
What people say it does
The old story was strychnine, and it was never true. A tab is far too small to carry a meaningful dose of anything else.
The modern version of the same story blames iso-LSD for body load, nausea and a hard come-up. DanceSafe puts the mechanism on the crude product as a whole, noting that only around 30% of it is LSD before purification and that the impurities are inactive in the brain while still having effects on the body.
The claim has a recognisable shape on forums. Someone has a rough night with heavy body load and thin visuals, someone else answers that the batch must have been high in iso-LSD, and the thread settles there. It is a tidy explanation for a bad night, and nobody has ever gone back and measured how much iso-LSD was actually in the tab.
Iso-LSD is the one thing in that mixture anyone has actually tested on people, and it came back with no effects at all. The body-load stories are about rough, unpurified product in general, not about iso-LSD on its own, and nobody has run the test that would tell the two apart. Treat it as untested rather than settled.
Reagents cannot detect iso-LSD
No colour test tells the two apart. Ehrlich and Hofmann react with a part of the molecule that both versions share, so the colour comes out the same whether the paper is mostly LSD or mostly iso-LSD. Nothing in a well or on a card changes that.
That matters most for the Hofmann colour scale. It reads everything on the paper at once, so two tabs can land on the same shade of violet and hold very different amounts of the version that works.
A reagent answers the question that puts people in hospital: whether the paper holds acid at all, or an NBOMe or DOC substitute. That takes about a minute. How much is iso-LSD is a strength question. What the substance is, is a safety question, and it comes first.
The method that does separate them
Separating the two on a chromatography plate is old, documented and repeatable. Two published methods cover it.
The table below lists the plate, the solvent and what each system shows, with the retention values as published.
| Source | Plate and solvent | Result |
|---|---|---|
| FDA, 1967 | Silica gel G, chloroform and methanol 1+4 | Both spots blue under UV, separated |
| FDA, 1967 | Silica gel G with alumina, acetone | LSD runs 0.6 to 0.7 cm, iso-LSD 0.3 to 0.4 |
| Clark, 1989 | Silica gel G, chloroform and methanol 9+1 | LSD at Rf 0.53, iso-LSD near 0.28 |
| Clark, 1989 | Silica gel G, acetone | LSD at Rf 0.58, iso-LSD near 0.17 |
Both compounds fluoresce bright blue under long-wave UV, so the plate is read by where the spots sit rather than by what colour they turn. Breakdown products appear as further spots at their own positions, which is how a plate tells a tired tab from a badly made one.
The Clark paper adds a trick. Heat the sample briefly in alcoholic potassium hydroxide before running it, and the base isomerises the LSD so that both C8 spots appear at once. Comparing that pair against LSD and iso-LSD standards is how analysts separate real LSD from close analogues such as LAMPA.
None of this is a home procedure. It needs coated plates, a UV lamp, a spray reagent and reference standards, and it gives you a separation rather than a number. Our own position on testing LSD quantity has not changed: a testing card will show you breakdown products, and it will not give you micrograms.
What a laboratory gives you
A laboratory separates the two and puts a number on each. Ours reports LSD in micrograms per blotter, which is the figure the iso-LSD share quietly moves.
That distinction is the whole point of a purity figure for a tab. Total material on the paper and active LSD on the paper are two different numbers, and the gap between them is the iso-LSD.
Blotter is accepted. Liquid is not, so if you are holding a dropper bottle the answer stops at identity.
Where these numbers come from
The stereochemistry and the Rf values are from Charles Clark, Journal of Forensic Sciences, volume 34, number 3, 1989, pages 532 to 546, and from Martin and Alexander, Journal of the AOAC, volume 50, number 6, 1967, page 1362. The 10% to 70% range and the use of the ratio for source attribution are reported in the forensic literature on illicit preparations. The 500 microgram figure is Hofmann’s.
LSD harm reduction guide · What Ehrlich reagent shows · What does LSD look like? · What a testing card does
Questions?
Is iso-LSD dangerous?
No. It has no measured effect of any kind, and the body-load stories are about rough product in general rather than iso-LSD on its own.
Does iso-LSD make my tab weaker?
Yes, in the sense that it takes up part of the dose without contributing to it. A tab that is mostly iso-LSD is a weak tab at full weight.
Can a reagent tell me how much iso-LSD is in it?
No. Both versions react the same way, so a reagent reports the two together. Telling you what the substance is, is what a reagent is for, and it does that in about a minute.
Can I separate them at home?
Not in any way that gives a number. The published separations need coated plates, a UV lamp and standards, and they stop at showing you two spots.
Why does the amount of iso-LSD change between batches?
Because it depends on how carefully the batch was finished. Nothing is added to make it, so the amount is a record of how the acid was produced.
Does old acid turn into iso-LSD?
Not really. Heat, light and damp mostly destroy the LSD outright rather than turning it into iso-LSD. Old acid is weaker because some of it has gone.
No test result can tell you a substance is safe. No substance is 100% safe.This article is published for harm reduction purposes. It does not encourage the use of psychoactive substances and does not replace medical advice.