The US Food and Drug Administration (FDA) should not approve TAP Pharmaceuticals' experimental anti-impotence drug, Uprima (apomorphine), said a Washington, DC-based consumer watchdog, Public Citizen, in a letter sent to the agency Monday.

Citing the marginal benefits of the product at its lowest dose, in addition to ``life-threatening toxicity'' at the highest dose, Public Citizen wrote that if the FDA approves the drug, ``it is certain that it will have to be banned within a short time after marketing begins.''

Uprima was developed by TAP Pharmaceuticals, a joint venture between Abbott Laboratories and Takeda Chemical Industries. The company is seeking FDA approval for three doses of the product -- 2 mg, 3 mg and 4 mg.

In its letter, the advocacy group founded by Ralph Nader warned that at the 4 mg dose level, incidence rates of adverse events, including nausea, dizziness, somnolence, hypotension and fainting, increased ``dramatically.''

``We're confident in Uprima,'' a TAP Pharmaceuticals spokeswoman told Reuters. ``TAP is currently working with the FDA and expects a response from the FDA on Uprima soon.''

The Public Citizen letter comes just days after the FDA issued a warning letter to TAP Pharmaceuticals, ordering the company to halt distribution of a news release that touted the benefits of Uprima while omitting the possible side effects.

The TAP release noted that nausea was the most commonly reported side effect from clinical trials of Uprima.

``You failed to disclose, however, material facts relating to significant and potentially life-threatening risks associated with Uprima'' that were presented at the panel meeting, the FDA warning letter read.

Federal law requires drug makers to provide a balanced picture of their products' benefits and risks in promotional materials.

The company pulled the news release cited in the FDA letter and has not reissued it.

If approved, Uprima would enter a possible US market of an estimated 30 million erectile dysfunction (ED) sufferers. Last year alone, Pfizer rang up more than $1 billion in sales of its blockbuster ED treatment, Viagra (sildenafil).