Review Describes Latest Findings on the Mechanisms of Psychedelic Drugs and Their Therapeutic Potential
In a 2021 review article in a special issue of the Journal of Neurochemistry devoted to “Psychedelics and Neurochemistry,” researcher Alaina M. Jaster and colleagues summarized recent findings on psychedelic drugs, including their potential as treatments for psychiatric disorders and the structural changes they produce in the brain. The review article focused on findings in humans and provided background context based on findings in animals, particularly rodents.
In the article, Jaster and colleagues write that psychedelics “have in common a battery of acute (within minutes to hours) effects in humans that include profound changes in processes related to perception, cognition, sensory processing, and mood.” They are not considered to be addictive, and recent research has identified fast-acting and long-lasting therapeutic effects of psychedelics, particularly for the treatment of depression and substance abuse.
While psychedelic drugs interact with the brain in complicated ways, the role of serotonin 5-HT2A receptors seems to be crucial to their effects. Psychedelics have classically been divided into two groups based on their chemical structures: phenethylamines (which include mescaline and its synthetic analog DOI) and tryptamines (which include psilocybin/“magic mushrooms,” DMT/ayahuasca, and ergolines like LSD, which are sometimes separated into a third category). The authors of the review highlight that other substances with different chemical structures that do not fit into this classification can also function as psychedelics. Examples include efavirenz and quipazine, which both activate serotonin 5-HT2A receptors and change rodent behavior in the same way that other psychedelic drugs do. These drugs are providing new directions for research into how psychedelics work at both serotonin 5-HT2A receptors and monoaminergic G protein-coupled receptors (GPCRs).
Rodent studies are often used to investigate how psychedelic drugs work. Rodent behaviors such as ear scratching and head twitching increase when the rodents are given drugs that have psychedelic effects in humans. These behaviors return to normal when rodents are given drugs that function as serotonin 5-HT2A receptor antagonists, preventing the stimulation of these serotonin receptors.
While it has been established that serotonin 5-HT2A receptors play an important role in the hallucinogenic effects of psychedelic drugs, how serotonin receptors are involved in some of the therapeutic effects of psychedelics, such as antidepressant effects and changes to synaptic plasticity, is not yet clear.
According to the review, “A number of studies in animal models as well as postmortem human brain samples from subjects with depression and controls has provided evidence that mood disorders occur in conjunction with a reduction in the density of dendritic spines, particularly in the frontal cortex.” Dendrites are the projections from the cell bodies of neurons upon which nerve endings from the axons of other neurons synapse. The surface of these dendrites is covered in mushroom-shaped spines that help create these synaptic connections. The review describes in vitro and in vivo research on mice that suggests that the psychedelics DOI, DMT, and LSD can remodel dendritic spines.
At a recent scientific meeting, researcher Javier González-Maeso, one of the authors of the review, described findings from a recent study of mice given DOI. The structure of the dendritic spines in the prefrontal cortex changed rapidly in these mice. They had also been conditioned to produce a fear response, and the extinction process to get rid of this learned fear was sped up in the mice given DOI. These effects occurred via the serotonin 5-HT2 receptors. The exposure to the psychedelic also affected the regulation of genes involved in synaptic assembly for days, suggesting that epigenetic-induced changes in synaptic plasticity may underlie some of the long-lasting therapeutic effects of psychedelics.
The review also addressed “microdosing,” the recreational practice of consuming small amounts of psychedelics such as psilocybin or LSD, based on the theory that amounts too small to create a hallucinogenic effect may instead produce therapeutic results. The authors find limited data to support microdosing. Most studies in humans and rodents have found no effect or, in the case of one rat study, a worsening of dendritic spine density following microdosing.
Psilocybin Comparable to Escitalopram in the Treatment of Depression
Four randomized, controlled clinical trials have established that psilocybin, the hallucinogenic compound in “magic mushrooms,” has anti-depressant effects. Recently, a phase 2 clinical trial compared the effects of psilocybin to a US Food and Drug Administration (FDA)–approved treatment for depression, the selective serotonin-reuptake inhibitor (SSRI) escitalopram. The study by Robin Carhart-Harris and colleagues was published in the New England Journal of Medicine in 2021.
The 59 participants in the 6-week study, which took place in the United Kingdom, had longstanding moderate-to-severe major depressive disorder. They were randomized to two groups. The psilocybin group received two separate doses of 25 mg of psilocybin 3 weeks apart, plus 6 weeks of daily placebo. The escitalopram group received two separate doses of 1 mg of psilocybin 3 weeks apart plus 6 weeks of daily oral escitalopram. (The small doses of psilocybin administered to the escitalopram group were assumed to have negligible psychiatric effects.) All participants were told they would receive psilocybin (though not the dose) in order to standardize their expectations.
In addition to the drug treatments, all participants also received psychological support, which consisted of monitoring immediately after the administration of the drugs (given the expectation that the 25mg dose of psilocybin would produce an “altered quality of conscious experience”), psychological debriefings, and an active listening session.
Psilocybin improved depression symptoms to a greater extent than escitalopram did. Among the participants, 70% of the psilocybin group responded to the treatment, compared with 48% of the escitalopram group. Remission occurred in 57% of the psilocybin group compared with 28% of the escitalopram group. These differences in the outcomes for the two groups were not statistically significant.
The FDA has designated psilocybin a “Breakthrough Therapy” for severe depression, which indicates that the therapy may be a substantial improvement over existing therapies for a serious condition. The designation is intended to speed up the drug development and review process.
The state of Oregon legalized psilocybin-assisted therapy in 2020.
MDMA Superior to Placebo in Treatment of Severe PTSD
An article by researcher Jennifer M. Mitchell and colleagues published in the journal Nature in 2021 reported that MDMA was more effective than placebo at treating severe post-traumatic stress disorder in an 18-week phase 3 clinical trial.
The article reported on a randomized, double-blind, placebo-controlled, multi-site trial that took place in the US, Canada, and Israel. Participants in the trial had severe PTSD, and in some cases also had dissociation, depression, a history of alcohol or substance use disorders, or childhood trauma. In the trial, 91 participants were required to stop any current psychiatric medications for a “washout” period, and then were randomized to either a group that received 12 therapy sessions plus placebo or a group that received 12 therapy sessions and 3 doses of MDMA, which were administered in a clinical setting.
Two months after the last therapy session, participants who had received MDMA during the trial showed greater reductions in PTSD symptoms and less functional impairment than those who were assigned to the placebo group during the trial. At the endpoint of the study, 67% of participants in the MDMA group no longer met the criteria for a PTSD diagnosis, compared to 32% of the placebo group.
Side effects that were more prevalent among the MDMA group were typically transient and mild to moderate in severity. These included muscle tightness, decreased appetite, nausea, sweating, feeling cold, and increased blood pressure and heartrate. The MDMA group did not show any increases in drug abuse or suicidality compared with the placebo group, and MDMA had similar effects among those participants with and without comorbid conditions. The authors concluded that MDMA was highly efficacious, safe, and well-tolerated as a treatment for PTSD and urged that further study of the treatment be done without delay.
Currently, US Food and Drug Administration (FDA)–approved treatments for PTSD include the selective serotonin reuptake inhibitors (SSRIs) sertraline and paroxetine, but approximately half of PTSD patients do not respond to these drugs or to evidence-based trauma-specific psychotherapy or cognitive-behavioral therapies. The FDA has designated MDMA-assisted therapy for PTSD a “Breakthrough Therapy.” This designation indicates that the therapy may be a substantial improvement over existing therapies for a serious condition, and is intended to speed up the drug development and review process.
MDMA (or 3,4-methylenedioxymethamphetamine) is the same chemical used recreationally under the name ecstasy or molly. However, the positive effects in the trial followed careful dosing (which is impossible with street drugs) and targeted therapy sessions.
Surface Area of Cortex Is Reduced After Multiple Manic Episodes
In a 2020 article in the journal Psychiatric Research: Neuroimaging, researcher Rashmin Achalia and colleagues described a study of structural magnetic resonance imaging (MRI) that compared 30 people with bipolar I disorder who had had one or several episodes of mania to healthy volunteers. Compared to the healthy volunteers, people with bipolar disorder had “significantly lower surface area in bilateral cuneus, right postcentral gyrus, and rostral middle frontal gyri; and lower cortical volume in the left middle temporal gyrus, right postcentral gyrus, and right cuneus.”
The surface area of the cortex in patients with bipolar I disorder who had had a single episode of mania resembled that of the healthy volunteers, while those who had had multiple manic episodes had less cortical surface area.
The data suggest that compared to healthy volunteers, people with bipolar disorder have major losses in brain surface area after multiple episodes that are not seen in first episode patients. In addition, the researchers found that both the number of episodes and the duration of illness was correlated with the degree of deficit in the thickness in the left superior frontal gyrus. These decreases in brain measures occurred after an average of only 5.6 years of illness.
Editor’s Note: These data once again emphasize the importance of preventing illness recurrence from the outset, meaning after the first episode. Preventing episodes may prevent the loss of brain surface and thickness.
Clinical data has also shown that multiple episodes are associated with personal pain and distress, dysfunction, social and economic losses, cognitive deficits, treatment resistance, and multiple medical and psychiatric comorbidities. These and other data indicate that treatment after a first episode must be more intensive, multimodal, and continuous and include expert psychopharmacological and psychosocial support, as well as family education and support. Intensive treatment like this can be life-saving. The current study also supports the mantra we have espoused: prevent episodes, protect the brain and the person.
Left Prefrontal Strokes Linked to Depression
In a 2021 article in the journal Stroke, researcher Julian Klingbeil and colleagues reported that left, but not right, ventrolateral prefrontal stroke lesions were associated with increased risk of depression at six months post-stroke.
The study included 270 participants who had their first-ever stroke. Six months following their strokes, 19.6% of the participants had depression. Those who scored higher on a scale of depression and anxiety symptoms in the first month after their stroke were more likely to have depression six months after the stroke.
The researchers identified a cluster of locations for stroke lesions, mostly within the left ventrolateral prefrontal cortex, that they linked to depression symptoms six months post-stroke. Klingbeil and colleagues hope that recognizing lesions in this region as risk factors for depression will help with early diagnosis of depression among people who recently had a stroke.
Editor’s Note: Antidepressants have been shown to improve post-stroke recovery of neurological functional (and depression) that is caused by the cutoff of blood supply during a stroke (ischemia). Patients and their family members should talk with their neurologist about treatment of ischemic strokes with antidepressants, especially when the lesions occur on the left side of the brain.
Psychiatric Disorders Linked to More Physical Disease
In an article in the journal JAMA Network Open, Leah S. Richmond-Rakerd and colleagues found that people with mental disorders had more physical disease at younger ages, they had more and longer hospitalizations and associated health care costs, and they were more likely to die at younger ages than people without mental disorders.
The research came from a population-based cohort study of more than 2.3 million citizens of New Zealand over three decades. The authors concluded, “These findings suggest that ameliorating mental disorders may have implications for improving the length and quality of life and for reducing the health care costs associated with physical diseases.”
Editor’s Note: This editor would suggest the importance of also doing the opposite, that is, looking out for and treating and preventing the physical illnesses to which psychiatric patients are more vulnerable in order to improve the length and quality of life.
Either way, medical illnesses, both physical and psychiatric, are intimately intertwined, and both deserve careful and early intervention. Psychiatric and physical illnesses cause suffering, disability, and early demise. Major psychiatric illnesses need to be seen as potentially lethal medical illnesses, a fact that few people realize. Conversely, physical illnesses are often not treated as aggressively or intensively in psychiatric patients as in the general population. For example, patients with bipolar disorder get fewer interventions with stents and bypasses for the same heart problems as others. Special attention needs to be given to better encourage and support the medical health of psychiatric patients.
ADHD Common in People with Mood Disorders
In a meta-analysis published in the journal Acta Psychiatrica Scandinavica in 2021, researcher Andrea Sandstrom and colleagues reported that people with mood disorders had a three times higher incidence of attention-deficit hyperactivity disorder (ADHD) than people without mood disorders. ADHD was also more likely to occur in people with bipolar disorder than in people with major depression. The comorbidity is most common in childhood, less so in adolescence, and lowest in adulthood.
Based on 92 studies including a total of 17,089 individuals, the prevalence of ADHD in people with bipolar disorder is 73% in childhood, 43% in adolescence, and 17% in adulthood. Data from 52 studies with 16,897 individuals indicated that prevalence of ADHD in major depressive disorder is 28% in childhood, 17% in adolescence, and 7% in adulthood.
Editor’s Note: A key implication of this research is that there is a huge overlap of bipolar disorder and ADHD in childhood, and that physicians need to specifically look for bipolar symptoms that are not common in ADHD to make a correct diagnosis. These include: brief or extended periods of mood elevation and decreased need for sleep in the youngest children; suicidal or homicidal thoughts and threats in slightly older children; hyper-sexual interests and actions; and hallucinations and delusions. When these are present, even when there are also clear-cut ADHD symptoms, a clinician must consider a diagnosis of bipolar disorder and treat the child with mood stabilizers prior to using stimulants or other traditional ADHD medications.
Conversely, physicians should be aware of the much lower incidence of ADHD in adolescents and adults with bipolar disorder. Here one should first make sure that the apparent ADHD symptoms of hyperactivity, inattention, poor concentration, etc. do not result from inadequately treated mania and depression, and if they do, treat these symptoms to remission prior to using traditional ADHD medications.
Study Examines Comorbidity of ADHD and Bipolar Disorder
In a 2021 review and meta-analysis in the journal Neuroscience and Biobehavioral Reviews, researcher Carmen Schiweck and colleagues described the comorbidity of attention-deficit hyperactivity disorder (ADHD) and bipolar disorder in adults. This was the first review and meta-analysis to quantify the comorbidity of the two fairly prevalent disorders. The meta-analysis included 71 studies with a combined total of 646,766 participants from 18 countries.
The review found that among people with ADHD, about 1 in 13 also have bipolar disorder, while among people with bipolar disorder, 1 in 6 have comorbid ADHD. The prevalence differed depending on the continent where patients lived and the diagnostic systems used there, with greater prevalence of both disorders in the US, where the Diagnostic and Statistical Manual of Mental Disorders is used, than in Europe, where the International Classification of Diseases is typically used. (Other parts of the world were less represented in the meta-analysis.) Schiweck and colleagues found that bipolar disorder had an onset about 4 years earlier in patients who had comorbid ADHD.
Insomnia Plays Critical Role in Bipolar Disorder
In a 2021 article in the Journal of Psychiatric Research, researcher Laura Palagini and colleagues reported that insomnia symptoms can affect the course of bipolar illness. In a helpful summary and interview in the Psychiatry & Behavioral Health Learning Network’s Psych Focus, she stated that:
“1) BD patients in a depressive phase with clinically significant insomnia met a greater severity not only of depressive symptoms and suicidal risk, but also of early life stressors and the cognitive part of hopelessness, compared with patients without insomnia
“2) insomnia symptoms could predict mood symptoms, suicidal ideation and plans, and the cognitive component of hopelessness
“3) insomnia symptoms might mediate the effect of early life stressors on mood symptoms, hopelessness, and suicidal ideation and behaviors.”
Palagini suggested that “Insomnia symptoms should be easily addressed in clinical practice with 1–2 questions. Insomnia treatment should be considered as a treatment to prevent …relapse and recurrence [of bipolar disorder] and to prevent suicide and the effect of early life stress on [bipolar disorder].”
Editor’s Note: Regular nightly rating of mood, functioning, hours of sleep, medications, life events, side effects, and other comorbid symptoms on the Monthly Mood Chart Personal Calendar (pdf) is an easy way for patients with bipolar disorder to carefully track their illness trajectory and the completeness of their response to medications.
A decrease in the hours of sleep should be used as a possible early warning sign of impending difficulties, or even a new episode. Patients should discuss with their physician the threshold of insomnia (such as the loss of 2 hours of sleep for two days in a row) that should trigger a call to the physician, and what interventions the patient might initiate for lesser amounts of sleep loss and/or changes in mood. Heading these off early may prevent the breakthrough of a full-blown manic or depressive episode.
Neurotransmitters Can Also Function As Epigenetic Marks
The most common epigenetic marks involve methylation of DNA (which usually inhibits gene transcription) and the acetylation and methylation of histones. Acetylation opens or loosens the winding of DNA around the histones and facilitates transcription, while methylation of histones leaves the DNA tightly wound and inhibits transcriptional activation.
Researcher Ashley E. Lepack and colleagues have identified a surprising type of epigenetic mechanism involving neurotransmitters. They report in a 2020 article in the journal Science that neurotransmitters such as serotonin and dopamine can act as epigenetic marks. Dopamine can bind to histone H3, a process called called dopaminylation (H3Q5dop). In rats undergoing withdrawal from cocaine, Lepack and colleagues found increased levels of H3Q5dop in dopamine neurons in a part of the midbrain called the ventral tegmental area (VTA), a part of the brain’s reward system. When the investigators reduced H3Q5dop, this decreased dopamine release in the reward area of the brain (the nucleus accumbens) and reduced cocaine seeking. Thus, dopamine can be both an important transmitter conveying messages between neurons and a chemical mark on histones that alters DNA binding and transcriptional regulation.
Researcher Jean-Antoine Girault provided commentary on the article by Lepack and colleagues, writing that “[t]he use of the same monoamine molecule as a neurotransmitter and a histone modification in the same cells illustrates that evolution proceeds by molecular tinkering, using available odds and ends to make innovations.”
Editor’s Note: Epigenetic marks may remain stable and influence behavior over long periods of time. They are involved in the increased reactivity or sensitization to repeated doses of cocaine through DNA methylation. Such sensitization can last over a period of months or longer. If the methylation inhibitor zebularine is given, animals fail to show sensitization. Now a newly identified epigenetic process, dopaminylation, is found to alter histones and is associated with long-term changes in cocaine-seeking.
The clinical message for a potential cocaine user is ominous. Cocaine not only creates a short-term “high,” but its repeated use rewires the brain not only at the level of changes in neurotransmitter release and receptor sensitivity, but also at the genetic and epigenetic level, changes that could persist indefinitely.
The sensitization to motor hyperactivity and euphoria that occur with cocaine use can progress to paranoia and panic attacks and eventually even seizures (through a process known as kindling).
The dopaminylation of histones in the VTA could lead to persistent increases in drug craving and addiction that may not be easily overcome. Thus, the appealing short-term effects of cocaine can spiral into increasingly adverse behaviors and drug-seeking can become all consuming. While these adversities do not emerge for everyone, the best way to ensure that they do not is to avoid cocaine from the start.
Manic episodes that include a feeling of invincibility, increased social contacts, and what the DSM-5 describes as “excessive involvement in pleasurable activities that have a high potential for painful consequences” are a time that many are at risk for acquiring a substance problem. For the adolescent who has had a manic episode, ongoing counseling about avoiding developing this type of additional long-term, difficult-to-treatment psychiatric illness could be lifesaving. Describing the epigenetic consequences of substance use may or may not be helpful, but may be worth a try.
