Speculation of tougher controls over testosterone drugs saw the sharemarket value of Acrux slashed by a quarter early on Thursday, before the shares were suspended from trading.

In a detailed statement, Acrux said a review panel of the Food and Drug Administration (FDA) found there was insufficient evidence that patients prescribed testosterone were at increased cardiovascular risk, although the results of some clinical studies which are due in the next six months or so may provide further information in this regard.

Concerns over adverse health effects from the drug have whipsawed the Acrux share price since February, when speculation that the over-use of the drug could cause cardiac arrests prompted heavy selling of its shares.

However the review panel did recommend the adoption of tougher controls over the content of the labelling of this class of drug.

Testosterone has become widely prescribed to men often for symptoms related to aging, which has prompted some criticism within health circles in the US.

"The whole idea is to try to rein in the inappropriate advertising and use of these drugs," the New York Times quoted Michael Domanski, the director of heart failure research at Mount Sinai School of Medicine, as saying. Dr Domanski was one of 20 members on the panel who voted to change the labelling, with only one member voting against the change.

Acrux executive chairman Ross Dobinson said he agreed with much of the recommendation of the panel, and his product was not pitched to age-related prescription of testosterone, which is behind some of the concerns over the use of the drug..

Acrux said the FDA is not obliged to follow the advice of its advisory panels, although the company did say "it is premature to speculate" how the FDA will respond to the panel's recommendation, and more particularly whether there will be any change by prescribing physicians.

"We don't expect anything startling in the new studies," Mr Dobinson said in reference to the additional studies underway into the cardiovascular effects of the use of testosterone.

Acrux is the owner and developer of Axiron which is sometimes prescribed for older men who suffer from low levels of natural testosterone. The US market for testosterone replacement therapy is estimated to have reached $US2 billion ($2.2 billion), which has prompted a backlash that perhaps the drugs are being over-prescribed.

Acrux has licensed the global rights for the product to Eli Lilly, receiving a royalty income stream.