Depression is a potentially life-threatening disease that is one of the leading causes of disability in the world. In 2017, more than 300 million people suffered from depression. That equates to about 4.4% of the world's population, making it the world's second most common public health disease after cardiovascular disease. About 50% who are treated for depression develop unipolar treatment-resistant depression, a type of severe persistent depression in which conventional methods or drugs do not have effect.  Psilocybin is a tryptamine found in a variety of species of psychedelic mushrooms. Psilocybin is a prodrug that breaks down into the active substance psilocin which interacts with serotonin receptors and produces psychoactive effects. Psilocybin is classified as a schedule I drug in most of the world and is therefore not considered to have any medical value. Psilocybin has been researched intensively in recent years, mainly focusing on its potential antidepressant effect. Psilocybin's effects have been widely covered in English literature but hardly at all in Swedish literature. This bachelor thesis will hopefully fill that gap and encourage more research on the subject here in Sweden. The purpose of this bachelor thesis was to evaluate, based on published studies, whether psilocybin potentially can have an effective, safe, and long-lasting antidepressant effect on depressive symptoms. Six studies are presented, and the results indicate that that 20–30 mg of psilocybin together with psychological support in an optimal environment can potentially have a long-acting, safe, and effective antidepressant effect on adult people with moderate to severe unipolar depression. Based on these results, the drug classification of psilocybin should be questioned and investigated.

Inledning: Depression är ett globalt folkhälsoproblem som drabbar människor i alla åldrar oavsett kön. En tredjedel av alla patienter diagnostiserade med depression blir inte hjälpta av dagens behandlingsmetoder och i synnerhet läkemedel. Denna grupp av individer klassificeras som behandlingsresistenta. För individer som lever med behandlingsresistent depression (TRD) är situationen allvarlig. Suicidala tankar (SI) och beteenden är vanligt förekommande och ökar i takt med svårighetsgraden av depressionen. Upptäckten av ketamins snabba effekter mot depression under 2000-talet har givit nytt ljus åt forskningen och mycket forskning görs på området som indikerar på positiva effekter mot TRD och de suicidala benägenheterna. Ketamin är dock ett problematiskt läkemedel med svåra biverkningar som gör situationen mer komplex. Syfte: Syftet med detta litteraturarbete var att undersöka effekterna av intravenöst (iv) ketamin mot TRD och i synnerhet dess antisuicidala effekter. Metod: Fem kliniska studier har analyserats. Två databassökningar gjordes via databasen PubMed med sökorden ”TRD suicidal ideation ketamine infusion treatment” och ” treatment resistant depression ketamine suicidal cognition”. Inkluderade artiklar valdes utifrån fastställda inklusions- och exklusionskriterier. Resultat: Överlag påvisas ett positivt resultat av ketamins antisuicidala effekter vid TRD. Fyra av fem studier visade signifikanta resultat av en singeldos ketamin jämfört med placebo och en studie kunde visa positiva effekter av upprepade infusioner. Medan en studies resultat varken kunde påvisa positiva effekter på kort eller lång sikt. Diskussion: Sammanfattningsvis indikerar resultatet av inkluderade studier på att ketamin i viss grad har positiva effekter på SI vid TRD och att iv ketamin har potential som läkemedel för denna patientgrupp. Dock krävs det mer forskning kring effektens hållbarhet, långtidseffekter, biverkningar och beroenderisken av ketamin. Idag används ketamin i form av det intranasala läkemedlet Spravato mot svår depression, detta med försiktighet på grund av de allvarliga biverkningar som kan följa och dess okända långtidseffekter. / Introduction: Depression is a global public health problem that affects people of all ages regardless of gender. One third of all patients diagnosed with depression are not helped by today's treatment methods. This group of individuals is classified as the treatment resistant. For individuals living with treatment-resistant depression (TRD), the situation is dire. Suicidal thoughts (SI) and behaviors are common and increase with the severity of the depression. The discovery of ketamine's rapid effects against depression in the 21st century has given new light to research and much research are being done in the area that indicates positive effects against TRD and the suicidal tendencies. However, ketamine is a problematic drug with severe side effects that make the situation more complex. Aim: The aim of this review was to investigate the effects of intravenous (iv) ketamine against TRD and in particular its anti-suicidal effects. Method: Five clinical studies have been analyzed. Two database searches were made via the PubMed database with the keywords "TRD suicidal ideation ketamine infusion treatment" and "treatment resistant depression ketamine suicidal cognition". Included articles were selected based on established inclusion and exclusion criteria. Results: Overall, a positive result of ketamine's anti-suicidal effects in TRD is demonstrated. Four out of five studies showed significant results of a single dose of ketamine compared to placebo and one study was able to show positive effects of repeated infusions. While the results of one study could not demonstrate positive effects in the short or long term. Discussion: In summary, the results of included studies indicate that ketamine has, to some extent, positive effects on SI in TRD and that iv ketamine has potential as a drug for this patient group. However, more research is needed concerningdurability of the effect, long-term effects, side effects and the risk of addiction to ketamine. Today, ketamine is used in the form of the intranasal drug Spravato against severe depression, this with caution because of the serious side effects that can follow and its unknown long-term effects.