About 70,000 under-18s are prescribed antidepressants each year, BBC analysis of NHS England figures shows.
According to clinical guidelines, external, children should be assessed by a psychiatrist before they are prescribed antidepressants.
However, Gloucestershire GP Tom Sutherland said “skyrocketing demand” for young people’s mental health services meant some doctors felt forced to prescribe medication outside of those guidelines.
“GPs often find themselves in a really difficult situation where [a patient’s] access to that specialist will be 18 months or two years away,” Sutherland added.
“They’re forced into a position where they can either not prescribe that medication, and there’s a potential harm there to the patient by being left untreated, or they can act outside of guidance and initiate that medication.
“There’s no good choice for GPs in the system as it is at the moment.”
Sutherland said patients at his surgery were never prescribed antidepressants in isolation and were referred to support services while they waited to see specialists.