Prozac rival makes you happy and sexy ... but sleepy and fat

A rival for the sunshine drug, Prozac, the fastest selling antidepressant in history, is to be launched next week, with claims that it is the most powerful mood-lifter yet discovered.

A powerful selling point of the new drug, to be sold under the brand name Zispin, is likely to be the absence of sexual side effects. Prozac, like most anti-depressants, causes anorgasmia - difficulty in achieving orgasm.

However, a drawback of Zispin (chemical name, mirtazapine) is that it also causes weight gain in some patients, in contrast to the weight loss associated with Prozac, and has a temporary sedative effect.

The new drug is a novel pharmaceutical compound that acts in a different way from Prozac and is claimed to be 40 per cent more effective in overcoming depression. It targets two neurotransmitters (brain chemicals), noradrenaline and serotonin, which are believed to be linked to depression, compared with the one, serotonin, influenced by Prozac (medical name, fluoxetine).

A six-week trial of Zispin in 140 patients, half of whom took the drug while the other half took Prozac, found that the mood of those on Zispin improved more rapidly and to a greater extent, as measured by a standard depression questionnaire, than those on Prozac.

Professor Chris Thompson, consultant psychiatrist at the Royal South Hants Hospital, Southampton, said the speed of improvement of patients on the new drug was astonishing. "It is unprecedented that a new antidepressant should provide an increase of efficacy of some 40 per cent over the market leader, fluoxetine." He said the most important issues were to replicate the findings and to get longer-term data.

Zispin is the first NaSSA - a Noradrenergic and Specific Serotonergic Antidepressant - acting on the two neurotransmitters, noradrenaline and serotonin, in contrast to the SSRI's - Selective Serotonin Re-uptake Inhibitors - such as fluoxetine, Prozac, which only influence serotonin. The manufacturers of Zispin, Organon Laboratories, claim this is why it is more powerful but has fewer side effects.