This thesis explores the pharmacological mechanisms of serotonergic psychedelics, primarily psilocybin and MDMA, in relation to neuroplasticity and their potential to treat post-traumatic stress disorder (PTSD). It reviews neurobiological pathways, including 5-HT2A receptor stimulation and brain-derived neurotrophic factor (BDNF) up-regulation, supporting synaptic growth and fear extinction. The thesis compares these psychedelics with ketamine and highlights clinical trial outcomes showing promising symptom reduction with psychedelic-assisted psychotherapy. Ethical, regulatory, and safety considerations for clinical use are discussed, emphasising the need for trauma-informed therapeutic protocols. The work underscores neuroplasticity as a key therapeutic target while calling for further PTSD-specific clinical research to establish treatment durability.