Studies have found that approximately one third of patients with depression will not respond well to a series of treatments.

Researchers outlined the latest evidence-based drug treatment strategies based on studies including an American trial of almost 3,000 patients. That trial found 30% of patients failed to achieve remission of their depression after using up to four different antidepressants.

Researchers say doctors treating people who haven’t responded well to treatment should consider other general clinical issues such as missed psychiatric diagnoses and unresolved psychological issues before adopting a pharmacological strategy.