Two top mental health specialists have joined a growing number of doctors and patients questioning the effectiveness of a controversial new antidepressant.
Psychiatrist David Codyre says the number of patients who've become unwell on the funded generic drug Enlafax is "a phenomenon".
More than 380 complaints have been lodged with the national centre monitoring adverse reactions.
But Pharmac is standing by it's decision to switch its funding from Effexor to Enlafax, citing the regulator Medsafe which claims the two drugs are pharmaceutically identical.
David Codyre, lead psychiatric adviser to 150 Auckland GP's, says while the number of adverse reactions is unusual, it's a real phenomenon.
"Even though on paper these are identical medicines, in real life they're behaving differently," he said.
"From a purely scientific perspective it's not explainable. And I think that's what Pharmac's problem is."
Psychiatrist Rob Shieff has also noticed problems in patients switching from Effexor to Enlafax, even asking patients who can afford it to pay for their old medication.
Pharmac says patients can apply for special funding but so far only one of the 37 applications have been approved.
Medsafe is seeking additional information from the manufacturer and checking with its regulation counterpart in Australia.