New Zealand's drug buying agency is warning people not to suddenly stop taking anti-depressants, despite suggestions they are largely ineffective.

British researchers carried out clinical trials on Prozac, Seroxat, Effexor and Serzone . They found the drugs work no better than a placebo.

Pharmac medical director Dr Peter Moodie says people who take anti-depressants should talk to their doctor or health professional. He says people need to discuss whether the medication is working for them and should not just stop taking it.

Dr Moodie says Pharmac plans to carefully analyse the findings. He says the benefits of many drugs can be minimal and people should be careful not to over hype them.

New Zealand issues about 720,000 prescriptions for anti-depressants every year.