LSD: dosage

LSD is very potent: only microgram amounts are needed to produce overt hallucinations [1]. The drug shows dose-proportional pharmacokinetics with first-order elimination, so higher doses produce higher exposure in a roughly linear fashion [2].

Subjective effects start at 25 µg [2]. Good drug effects plateau at 100 µg — going higher doesn't add more of the effects people are usually seeking [2]. But other effects keep changing past that ceiling: 200 µg produces greater ego dissolution than 100 µg [2], and also produces significant anxiety [2]. More is not simply "more of the same."

Duration lengthens with dose. Across the 25–200 µg range, average duration of subjective effects increases from 6.7 to 11 hours [2]. Separately, effects have been reported to begin 30 to 60 minutes after ingestion and last 10 to 12 hours [1].

For comparison, 100 µg and 200 µg LSD produce subjective effects comparable to 30 mg psilocybin, and both are clearly stronger than a 15 mg psilocybin dose [3]. LSD's effects last clearly longer than psilocybin's at equivalent intensity [3]. Dose equivalence across substances is not a reason to eyeball a switch: at matched intensity, LSD still lasts clearly longer than psilocybin.

Chronic use of serotonergic antidepressants has been reported to blunt LSD's subjective effects [4]; in one report, 88% of people on a serotonin reuptake inhibitor for over three weeks had a reduced or virtually eliminated response [4]. This is not a reason to compensate with a larger dose. Lithium combined with psychedelics has been linked in anecdotal reports to seizures in a substantial share of cases [5], and to bad trips [5], with a notable proportion of lithium reports involving medical attention [5]; only 8% of lithium reports were judged not to affect the experience at all [5]. Lamotrigine reports showed no seizures in the same kind of dataset [5], and most were judged not to affect the experience at all [5].

References

1. D-Lysergic Acid Diethylamide (drug fact sheet) — DEA Diversion Control Division
2. Acute dose-dependent effects of lysergic acid diethylamide in a double-blind placebo-controlled study in healthy subjects — Neuropsychopharmacology (Nature)
3. Direct comparison of the acute effects of lysergic acid diethylamide and psilocybin in a double-blind placebo-controlled study in healthy subjects — Neuropsychopharmacology (Nature)
4. Chronic administration of serotonergic antidepressants attenuates the subjective effects of LSD in humans — Neuropsychopharmacology (Nature)
5. Classic Psychedelic Coadministration with Lithium, but Not Lamotrigine, is Associated with Seizures: An Analysis of Online Psychedelic Experience Reports — Pharmacopsychiatry (Thieme)