Many Trips, Diminishing Returns: Cross-Tolerance Between LSD and DOI

Psychedelic drugs like LSD powerfully alter consciousness and promote neural plasticity, but drug tolerance occurs rapidly following the first dose. Although the mechanisms that underlie psychedelic tolerance may overlap with those that confer a therapeutic effect, until recently these mechanisms were unknown.


One and Done: Rapid Therapeutic Effects of Psychedelics

Clinical interest in the use of psychedelic drugs for the treatment of psychiatric disorders has recently exploded, with researchers testing the effects of compounds like LSD and psilocybin on patient populations that are resistant to traditional pharmacotherapies.1-4 The profound alterations in consciousness, sensory perception, and emotional state elicited by psychedelics depends on the ability of these drugs to bind to and activate the 5-HT2Areceptor.4-6 Further, activation of this receptor with specific research chemical agonists like DOI confers therapeutic effects in animal models relevant to human disorders like depression, anxiety, and addiction.7-9

The hallucinogenic properties of naturally-occurring psychedelics and their synthetic analogs can be modeled in mice using the head-twitch response (HTR), which reliably correlates with 5-HT2A activation and serves as a behavioral proxy of the “psychedelic trip” experienced by humans.10-12 Pharmacological blockade of 5-HT2A receptors reduces the psychedelic-induced HTR response in rodents and suppresses the subjective effects of psychedelics in human participants.10-13 Although not established indisputably, 5-HT2A receptor activation and downstream neural plasticity may be necessary for many of the therapeutic effects of psychedelics as well.9,13

Losing Reception: Mechanisms of Drug Tolerance

The 5-HT2A receptor, the primary target of psychedelics, is a G-protein coupled receptor (GPCR).4,13 This family of receptors includes the targets of many other psychoactive drugs, including stimulants and opioids.14,15 As with other GPCRs, 5-HT2A receptors are subject to processes like upregulation and downregulation in response to drug exposure or experience.15-26 The process of receptor downregulation following repeated drug exposure engenders a state of drug tolerance, characterized by an attenuated response to the same amount of drug.14,24-26

Opioid tolerance is perhaps the best studied form of drug tolerance, and develops after repeated exposure to commonly used opioids.14,15 Opioid tolerance reduces both the analgesic and euphoric effects of opioids, limiting their therapeutic or recreational effects at the same dose and thus requiring dose escalation to achieve the desired effects.15 Opioids target a GPCR known as the μ opioid receptor (μOR), which are internalized after repeated activation through signaling pathways that occur inside cells and involve proteins called arrestins.14,15 Because most commonly used opioids target the μOR, chronic exposure to an opioid like oxycodone would also produce “cross-tolerance” to other opioids like morphine, even if the person had never taken morphine before.14,15

There is some evidence of tolerance and cross-tolerance to psychedelics, but many of these studies did not meet present day methodological standards and questions remain about the mechanisms that might be involved.16-26 Moreover, while arrestins are typically conceptualized as simple “chaperones” that internalize GPCRs to bring them offline after prolonged activation, their intracellular signaling capacity is in fact much more complex.14,15 For instance, arrestins like ꞵ-arrestin-2 (ꞵArr2) can act as a “scaffold” for a broad range of proteins that control transcriptional and translational programs important for neural plasticity.14  Further study of how psychedelics alter 5-HT2A receptor expression and initiate 5-HT2A-dependent adaptations in neurons may be clinically important, as these same changes may underlie the therapeutic effects of these drugs.9,13,24-26

Question and Approach

In a new study, de la Fuente Revenga and colleagues set out to investigate the development of tolerance and cross-tolerance to multiple chemical classes of psychedelics by using the phenethylamine DOI and the ergoline LSD in mice with the HTR model of drug effects.27 For comparison, they also tested the effects of the non-psychedelic 5-HT2A agonist lisuride on tolerance and cross-tolerance to DOI and LSD.27  In addition, the researchers examined the effects of 5-HT2A receptor blockade with the specific antagonist M100907 on the development of psychedelic tolerance, as well as the effect of genetic of ꞵArr2 using special ꞵArr2 knockout (ꞵArr2 KO) mice.27,28

Major Findings

  1. Tolerance to DOI and LSD as assessed by the HTR in mice revealed diminished responses to both drugs following repeated once-daily exposure (both 24 hours and 4 days after), suggesting that psychedelic drugs induce rapid drug tolerance. This phenomenon was accompanied by a ~50% downregulation of 5-HT2A receptors in the frontal cortex of mice 24 hr after DOI exposure, as measured by a binding assay of receptor density.
  2. Diminished responses to DOI following repeated LSD exposure, but not lisuride, indicate that cross-tolerance develops only for the psychedelic 5-HT2A agonists.
  3. Blockade of the 5-HT2A receptor with the antagonist M100907 predictably reduced the initial HTR response elicited by DOI, but also reduced the  development of tolerance after repeated exposures. However, in the absence of the antagonist, tolerance to DOI in the HTR assay could be overcome by doubling the dose on test day.
  4. Development of drug tolerance to DOI was unchanged in ꞵArr2 KO mice, indicating that downregulation of 5-HT2A receptors and reduced sensitivity to DOI do not depend on ꞵArr2 signaling.

Psychedelic Tolerance: Big Picture and Clinical Implications

This elegant, detailed study by de la Fuente Revenga and colleagues establishes that psychedelic 5-HT2A agonists produce tolerance and cross-tolerance after repeated exposures, and sheds light on biological targets that are required or dispensable for this phenomenon. The finding that lisuride, a 5-HT2A agonist devoid of hallucinogenic potential, does not elicit cross-tolerance is fascinating, but further studies are necessary to clearly delineate the molecular differences in drug binding and 5-HT2A receptor dynamics responsible for this difference.3,9,13,28

Downregulation of 5-HT2A receptors in the frontal cortex after DOI exposure, observed in this study as well as in previous studies, corroborates that reduced availability of this receptor likely contributes to psychedelic tolerance as part of a homeostatic response.24-27 Second-generation antipsychotic drugs like clozapine and quetiapine block the 5-HT2A receptor as antagonists but still reduce the availability of this receptor.29 Thus, homeostatic downregulation of 5-HT2A receptors elicited by psychedelics (agonists) or antipsychotics (antagonists) could indicate partially overlapping common therapeutic mechanisms between these disparate drug classes.4,9,13,29 Lastly, the finding that psychedelic tolerance is independent of ꞵArr2 signaling raises interesting questions about novel, atypical signaling pathways that regulate the expression of the 5-HT2A receptor.14,30 Future studies aimed at answering these questions will be important to establish a clear model of the mechanism of action of psychedelics in the context of treating psychiatric disease.1-4

Daniel Lustberg headshot

Danny Lustberg received his PhD in Molecular & Systems Pharmacology from Emory University in 2022. He is currently a postdoctoral researcher at Emory University, studying the role of the central noradrenergic system in stress-related psychiatric diseases, including anxiety disorders and OCD.


Notify of

Newest Most Voted
Inline Feedbacks
View all comments
sian olsen
1 year ago

Short & sweet summary.
Big Thx Daniel.
Come visit the Big Isle, and we’ll take you out on the water. Boat, SUP, etc.

Danny Lustberd
1 year ago
Reply to  sian olsen

how can i say no to that?!

George Falco
1 year ago

It’s a shame research had to end years ago

  1. Carhart-Harris RL, Goodwin GM. The Therapeutic Potential of Psychedelic Drugs: Past, Present, and Future. Neuropsychopharmacology. 2017;42(11):2105-2113. doi:10.1038/npp.2017.84
  2. Nutt D. Psychedelic drugs-a new era in psychiatry?. Dialogues Clin Neurosci. 2019;21(2):139-147. doi:10.31887/DCNS.2019.21.2/dnutt
  3. McClure-Begley TD, Roth BL. The promises and perils of psychedelic pharmacology for psychiatry. Nat Rev Drug Discov. 2022;21(6):463-473. doi:10.1038/s41573-022-00421-7
  4. Mestre TA, Zurowski M, Fox SH. 5-Hydroxytryptamine 2A receptor antagonists as potential treatment for psychiatric disorders. Expert Opin Investig Drugs. 2013;22(4):411-421. doi:10.1517/13543784.2013.769957
  5. González-Maeso J, Weisstaub NV, Zhou M, et al. Hallucinogens recruit specific cortical 5-HT(2A) receptor-mediated signaling pathways to affect behavior. Neuron. 2007;53(3):439-452. doi:10.1016/j.neuron.2007.01.008
  6. Kometer M, Schmidt A, Jäncke L, Vollenweider FX. Activation of serotonin 2A receptors underlies the psilocybin-induced effects on α oscillations, N170 visual-evoked potentials, and visual hallucinations. J Neurosci. 2013;33(25):10544-10551. doi:10.1523/JNEUROSCI.3007-12.2013
  7. De Gregorio D, Inserra A, Enns JP, et al. Repeated lysergic acid diethylamide (LSD) reverses stress-induced anxiety-like behavior, cortical synaptogenesis deficits and serotonergic neurotransmission decline. Neuropsychopharmacology. 2022;47(6):1188-1198. doi:10.1038/s41386-022-01301-
  8. Jaster AM, Elder H, Marsh SA, de la Fuente Revenga M, Negus SS, González-Maeso J. Effects of the 5-HT2A receptor antagonist volinanserin on head-twitch response and intracranial self-stimulation depression induced by different structural classes of psychedelics in rodents. Psychopharmacology (Berl). 2022;239(6):1665-1677. doi:10.1007/s00213-022-06092-x
  9. De Gregorio D, Enns JP, Nuñez NA, Posa L, Gobbi G. d-Lysergic acid diethylamide, psilocybin, and other classic hallucinogens: Mechanism of action and potential therapeutic applications in mood disorders. Prog Brain Res. 2018;242:69-96. doi:10.1016/bs.pbr.2018.07.008
  10. Canal CE, Morgan D. Head-twitch response in rodents induced by the hallucinogen 2,5-dimethoxy-4-iodoamphetamine: a comprehensive history, a re-evaluation of mechanisms, and its utility as a model. Drug Test Anal. 2012;4(7-8):556-576. doi:10.1002/dta.1333
  11. de la Fuente Revenga M, Vohra HZ, González-Maeso J. Automated quantification of head-twitch response in mice via ear tag reporter coupled with biphasic detection [published online ahead of print, 2020 Jan 16]. J Neurosci Methods. 2020;334:108595. doi:10.1016/j.jneumeth.2020.108595
  12. de la Fuente Revenga M, Shin JM, Vohra HZ, et al. Fully automated head-twitch detection system for the study of 5-HT2A receptor pharmacology in vivo. Sci Rep. 2019;9(1):14247. Published 2019 Oct 3. doi:10.1038/s41598-019-49913-4
  13. Jaster AM, de la Fuente Revenga M, González-Maeso J. Molecular targets of psychedelic-induced plasticity. J Neurochem. 2022;162(1):80-88. doi:10.1111/jnc.15536
  14. Littleton J. Receptor regulation as a unitary mechanism for drug tolerance and physical dependence--not quite as simple as it seemed!. Addiction. 2001;96(1):87-101. doi:10.1046/j.1360-0443.2001.961877.x
  15. Zuo Z. The role of opioid receptor internalization and beta-arrestins in the development of opioid tolerance. Anesth Analg. 2005;101(3):728-734. doi:10.1213/01.ANE.0000160588.32007.AD
  16. Cholden LS, Kurland A, Savage C. Clinical reactions and tolerance to LSD in chronic schizophrenia. J Nerv Ment Dis. 1955;122(3):211-221. doi:10.1097/00005053-195509000-00001
  17. Abramson HA, Sklarofsky B, Baron MO, Fremont-Smith N. Production of tolerance to psychosis-producing doses of lysergic acid diethylamide. Science. 1957;126(3281):1020. doi:10.1126/science.126.3281.1020
  18. Freedman DX, Aghajanian GK, Ornitz EM. Patterns of tolerance to lysergic acid diethylamide and mescaline in rats. Science. 1958;127(3307):1173-1174. doi:10.1126/science.127.3307.1173
  19. Balestrieri A, Fontanari D. Acquired and crossed tolerance to mescaline, LSD-25, and BOL-148. AMA Arch Gen Psychiatry. 1959;1:279-282. doi:10.1001/archpsyc.1959.03590030063008
  20. Isbell H, Wolbach AB, Wilker A, Miner EJ. Cross tolerance between LSD and psilocybin. Psychopharmacologia. 1961;2:147-159. doi:10.1007/BF00407974
  21. Buchborn T, Lyons T, Knöpfel T. Tolerance and Tachyphylaxis to Head Twitches Induced by the 5-HT2A Agonist 25CN-NBOH in Mice. Front Pharmacol. 2018;9:17. Published 2018 Feb 6. doi:10.3389/fphar.2018.00017
  22. Buchborn T, Schröder H, Dieterich DC, Grecksch G, Höllt V. Tolerance to LSD and DOB induced shaking behaviour: differential adaptations of frontocortical 5-HT(2A) and glutamate receptor binding sites. Behav Brain Res. 2015;281:62-68. doi:10.1016/j.bbr.2014.12.014
  23. Smith DA, Bailey JM, Williams D, Fantegrossi WE. Tolerance and cross-tolerance to head twitch behavior elicited by phenethylamine- and tryptamine-derived hallucinogens in mice. J Pharmacol Exp Ther. 2014;351(3):485-491. doi:10.1124/jpet.114.219337
  24. Gresch PJ, Smith RL, Barrett RJ, Sanders-Bush E. Behavioral tolerance to lysergic acid diethylamide is associated with reduced serotonin-2A receptor signaling in rat cortex. Neuropsychopharmacology. 2005;30(9):1693-1702. doi:10.1038/sj.npp.1300711
  25. Buckholtz NS, Freedman DX, Middaugh LD. Daily LSD administration selectively decreases serotonin2 receptor binding in rat brain. Eur J Pharmacol. 1985;109(3):421-425. doi:10.1016/0014-2999(85)90407-8
  26. McKenna DJ, Nazarali AJ, Himeno A, Saavedra JM. Chronic treatment with (+/-)DOI, a psychotomimetic 5-HT2 agonist, downregulates 5-HT2 receptors in rat brain. Neuropsychopharmacology. 1989;2(1):81-87. doi:10.1016/0893-133x(89)90010-9
  27. de la Fuente Revenga M, Jaster AM, McGinn J, Silva G, Saha S, González-Maeso J. Tolerance and Cross-Tolerance among Psychedelic and Nonpsychedelic 5-HT2A Receptor Agonists in Mice. ACS Chem Neurosci. 2022;13(16):2436-2448. doi:10.1021/acschemneuro.2c00170
  28. Rodriguiz RM, Nadkarni V, Means CR, et al. LSD-stimulated behaviors in mice require β-arrestin 2 but not β-arrestin 1. Sci Rep. 2021;11(1):17690. Published 2021 Sep 3. doi:10.1038/s41598-021-96736-3
  29. Moreno JL, Holloway T, Umali A, Rayannavar V, Sealfon SC, González-Maeso J. Persistent effects of chronic clozapine on the cellular and behavioral responses to LSD in mice. Psychopharmacology (Berl). 2013;225(1):217-226. doi:10.1007/s00213-012-2809-7
  30. Bhatnagar A, Willins DL, Gray JA, Woods J, Benovic JL, Roth BL. The dynamin-dependent, arrestin-independent internalization of 5-hydroxytryptamine 2A (5-HT2A) serotonin receptors reveals differential sorting of arrestins and 5-HT2A receptors during endocytosis. J Biol Chem. 2001;276(11):8269-8277. doi:10.1074/jbc.M006968200