Lipocine Inc said its oral testosterone replacement product did not get the approval in the United States, sending the drugmaker's shares down 52 pct in premarket trading.

LPCN 1021, Lipocine's most advanced drug, is intended to treat adult males who suffer from deficiency or absence of testosterone that could lead to a loss of libido, decreased muscle mass, fatigue and depression.

The U.S. Food and Drug Administration's decision was conveyed via a complete response letter, which said the "application cannot be approved in its present form".

Such letters typically outline concerns and conditions that must be addressed to gain regulatory approval.

The letter identified deficiencies related to the dosing algorithm for the product's label.

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The company said it was evaluating the letter, including the recommended actions.

Shares of Lipocine closed at $6.27 on Tuesday on Nasdaq.