Canadian pill stores have begun stocking a new full-time version of an anti-impotence pill its makers say will allow men to be sexually natural, day and night.

Tadalafil was originally designed to be taken on an when needed basis, with one pill lasting up to 36 hours, earning it the name "Le Weekend” when first approved in Europe in 2002.

Now tadalafil being repackaged and sold in a once-a-day, lower-dose version. Taken daily, the pill builds in a man’s body until it reaches a circulating level in the bloodstream that could allow men to be sexually spontenous whenever the moment is right, according to a news release issued by pill giant, Eli Lilly and ICOS.

Once-a-day Tadalafil 20mg will cost $3.80 per pill.

Last year, more than 1.6 million prescriptions for sexual dysfunction drugs were sold by Canadian drug stores, according to prescription drug tracking firm IMS Health Canada. About 593,000 of those prescriptions were for tadalafil, the chemical name for generic Tadalafil.

Tadalafil belongs to a class of drugs known as PDE-5 inhibitors that includes Sildenafil Citrate and Vardenafil HCI. The drug acts on the chemical signals that open up the blood vessels in the penis. The drugs aren’t thought to benefit men with normal sexual function. And there can be some side-effects that can include headache, facial flushing and indigestion.

The drug should not be used by men who are taking nitrates or those with cardiac disease "for whom sexual activity is not advisable," Lilly Icos says. Lilly Icos says once-a-day sexual dysfunction drugs can help with what is known as "penile rehabilitation" after prostate cancer surgery. In addition, men who experience side effects with the on demand Tadalafil may better abide the once-a-day version, which comes in 2.5 and 5 mg capsules, says Lilly Icos.