This compound showed euphoria, psychostimulation, increased appetite, and improved sleep as the side effects. Iproniazid, an antitubercular compound, was the first medication got reported for its antidepressant effect. Bupropion, an antidepressant medication got approved by the United States Food and Drug Administration (US-FDA) for smoking cessation, botulinum toxin A, the compound used for eye muscle disorders with cosmetic impacts and minoxidil, the antihypertensive medication, became established for pattern hair loss in male and female are some instances of well-known repurposed drugs. The positive outcome in multiple myeloma led to further derivative developments like lenalidomide. Decades later, in 1999, thalidomide was discovered to be effective in multiple myeloma. In 1964, thalidomide was fortuitously recognized to be effective in erythema nodosum leprosum (ENL). In consequence, thalidomide was withdrawn for four years. Thalidomide is another well-known instance causing many severe skeletal birth defections in children whose mothers had taken this medication during the first trimester of pregnancy. The year sildenafil got marketed by Pfizer for erectile dysfunction under the name Viagra В®, it held a 47% share of this problemвЂ™s market, and the total sales were USD 2.05 billion worldwide. Sildenafil citrate was an antihypertensive medication that got repurposed as retrospective clinical data analysis showed its positive effect on erectile dysfunction. So far, the most successful repurposed drugs have been found accidentally, and no systematic approach has been involved in the process.

Drug repurposing was serendipitous and accidental in the past whenever a medication had shown an off-target or a new on-target effect, it was investigated for commercial exploitation. Drug repurposing can emerge in different forms like repositioning, reformulation, and combination. Investigational medicines may have had a desirable safety profile in phase I/II clinical trials but never reached the market due to reasons unrelated to safety, such as lack of efficacy. However, they need proper studies in terms of formulation, matching with regulatory standards, and efficacy.Дrug repurposing is the procedure of finding new indications for approved or investigational medications. NeurotransmittersвЂ™ antagonists, atypical antipsychotics, and CNS stimulants have been studied for the repurposing aims. This review aims to discuss the available treatments and their progress way during repositioning. Considering the mentioned mechanisms has resulted in repurposed medications to treat treatment-resistant depression (TRD) as alternative approaches. In addition to reducing neurotransmitters like epinephrine and serotonin, other mechanisms such as inflammation, insufficient blood supply, and neurotoxicants are now considered as the possible involved mechanisms. A deeper understanding of the pathogenesis of depression encourages novel discoveries through drug repurposing and drug repositioning to treat depression.

Experimental studies and off-label use of drugs have helped drive data for further studies of approving these medications. A slow rate of new drug discovery and higher costs of new drug development attracted the attention of scientists and physicians for the repurposing and repositioning of old medications.

Delsym side effects hallucination