Respiratory centre depression can be caused by all except:

Ref:Parikh's Textbook of Medical Jurisprudence 6/e p10,57 *Strychnine stimulates the respiratory centre whereas other drugs given the option like opioids, barbiturates and gelsemium cause respiratory depression. *Gelsemium has been traditionally been used to treat pain and respiratory ailments. Toxic symptoms include giddiness, weakness, ptosis, dilated pupils and respiratory depression.