Stimulants that act on the central nervous system have been used since antiquity for ritual and other uses. Organic chemistry techniques, especially those developed in Germany in the late 1800s, resulted in the isolation and structural determination of several important stimulants. Synthetic pathways for amphetamine and related stimulants were developed in the first half of the 19th century, and these new drugs were widely marketed. Awareness of abuse potential emerged soon after but was contested. Stimulants have been used to counteract fatigue and promote wakefulness during military operations, as well as to treat sleep disorders, since the 1930s. Methylphenidate was approved to treat children with behavioral problems in 1962, predating the recognition of attention deficit hyperactivity disorder (ADHD). Stimulant abuse became a political concern in the post-war period, initially with the use of “pep-pills” by long-haul truck drivers and later as drug dealing became common in night clubs, with new laws limiting availability passed in the early 1960s. They have also been used to increase athletic and cognitive performance. Stimulants are still first-line therapies for ADHD and some sleep disorders; however, newer-generation drugs have been developed with better safety profiles and lower abuse potential. Illicit stimulant use continues to be common in many countries.

Ketamine, originally synthesized in 1962, has gained increasing attention due to its rapid and sustained antidepressant effects in treatment-resistant depression (TRD). Unlike traditional antidepressants, ketamine acts on multiple neurotransmitter systems, including NMDA receptor antagonism and AMPA receptor potentiation, offering a novel mechanism for mood regulation. Beyond psychiatry, ketamine remains a valuable anesthetic and analgesic agent with applications in acute and chronic pain management. Its anti-inflammatory, neuroprotective, and potential antitumor properties further underscore its versatility in clinical medicine. Despite its therapeutic promise, ketamine poses challenges due to its dissociative and hallucinogenic effects, contributing to widespread recreational use. Chronic misuse is associated with adverse health outcomes, including bladder dysfunction and hepatobiliary complications. As a result, ketamine has been subject to increasing regulatory scrutiny, balancing its medical utility with concerns about abuse potential. The rediscovery of ketamine’s antidepressant effects in the early 2000s has revolutionized psychiatric treatment, particularly in TRD and suicidality. Recent studies have also explored its efficacy in bipolar depression, posttraumatic stress disorder, obsessive-compulsive disorder, and substance use disorders, expanding its therapeutic applications. Additionally, ongoing research aims to elucidate its long-term effects and optimize dosing regimens to maximize clinical benefits while minimizing risks. This review highlights ketamine’s multifaceted pharmacological properties, its evolution from an anesthetic to a novel psychiatric treatment, and its broader medical applications. As research advances, a comprehensive understanding of ketamine’s mechanisms and clinical implications will be crucial for optimizing its therapeutic potential while mitigating its risks.

In recent times, several longitudinal studies aimed at clarifying whether cannabis use during adolescence might play a causal role in the subsequent risk of developing bipolar disorder have been published. Although their methodological heterogeneity precludes any meta-analytic approaches, evidence from these studies can be systematically evaluated using the Bradford Hill criteria. A biological gradient is supported by evidence on the dose–response relationship between exposure severity and outcome. As such, the effect of cannabis use on bipolar disorder onset is likely to be strong, coherent, plausible, and based on a clear temporality. In addition, some analogies can be hypothesized between studies testing the possible causal role of cannabis in the development of bipolar disorder and those is schizophrenia. Cannabis may represent a precipitating agent inducing bipolar disorder in a multicausal model of individual vulnerability. However, this relationship seems to be only partially consistent and nonspecific, and the experimental evidence is strongly suggestive but, as yet, inconclusive. Nevertheless, in summary, it seems there is sufficient support for the hypothesis that cannabis use during adolescence may play a causal role in bipolar disorder, although further studies are needed to consolidate the evidence.

Parkinson’s disease (PD) is a severe neurodegenerative disorder characterized by prominent motor and non-motor (e.g., cognitive) abnormalities. Notwithstanding Food and Drug Administration (FDA)-approved treatments (e.g., L-dopa), most persons with PD do not adequately benefit from the FDA-approved treatments and treatment emergent adverse events are often reasons for discontinuation. To date, no current therapy for PD is disease modifying or curative. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are central nervous system (CNS) penetrant and have shown to be neuroprotective against oxidative stress, neuroinflammation, and insulin resistance, as well as promoting neuroplasticity. Preclinical evidence suggests that GLP-1RAs also attenuate the accumulation of α-synuclein. The cellular and molecular effects of GLP-1RAs provide a basis to hypothesize putative therapeutic benefit in individuals with PD. Extant preclinical and clinical trial evidence in PD provide preliminary evidence of clinically meaningful benefit in the cardinal features of PD. Herein, we synthesize extant preclinical and early-phase clinical evidence, suggesting that GLP-1RAs may be beneficial as a treatment and/or illness progression modification therapeutic in PD.