It depends on what people mean by “strongest,” so it’s important to define some terms first.
Potency refers to the amount of a drug needed to produce a given effect. Although it sounds like a generic term, it has a precise pharmacological meaning. Potency is typically expressed as EC50, the concentration of a drug required to activate 50% of its receptors, usually measured in vitro in a cell culture or receptor assay. The lower the EC50, the higher the potency.
For example, approximate EC50 values at the 5HT2a receptor:
| Ligand | EC50 (nM) | EC50 (ug/L) |
| Serotonin | 30 | 5~ |
| DMT | 50 | 9~ |
| LSD | 1.5 | 0.5~ |
Affinity describes how tightly a molecule binds to a receptor, typically expressed as Ki. It measures how well a ligand can compete with other molecules (usually the natural ligand) for binding. High affinity does not necessarily mean strong activation. The affinities for serotonin, DMT and LSD are 30nM, 127nM and 2-3nM respectively.
Efficacy (or intrinsic activity) measures how strongly a ligand activates a receptor once bound. A full agonist has high efficacy, while a partial agonist has lower efficacy. This is usually expressed as a unitless ratio relative to the natural ligand.
So, LSD binds extremely tightly to 5-HT2A but only partially activates it compared to serotonin. DMT binds less tightly then serotonin but is almost a full agonist.
When people talk about the “strongest” psychedelic, they usually mean what feels strongest, which is subjective. By this measure, DMT and 5-MeO-DMT are often considered the most intense experiences. This isn’t because they bind particularly tightly to 5-HT2A, but because they act at multiple receptors, including 5-HT1A. There are "psychedelics" with virtually no interactions with 2a such as 5-MeO-pyr-T which is all 1a and is reportedly very very intense.
If you ask a pharmacologist about the strongest 5-HT2A agonists, compounds like the NBOMe series are notable. Many of them have very high affinity and are often "super agonists" meaning they have a higher efficacy then even serotonin.
Of course, this is a massive oversimplification. Many other factors influence a drug’s effects, including how it’s processed by the body (pharmacokinetics), exactly where it binds on the receptor, which signaling pathways it activates, and numerous other variables.
People aren't wrong when they call DMT the strongest, because subjectively it is.