Shares of GW Pharmaceuticals (GWPH) surged in after-market trading Tuesday. This was on the back of the company's fiscal 2019 second-quarter results, which were released after market close.

As with other marijuana stocks lately, GW Pharmaceuticals posted immense growth on the top line. The quarter's revenue came in at just over $72 million, far above the $3.3 million in the same period last year. This result easily surpassed the average analyst expectation of $47 million.

A cannabis leaf lying near a stethoscope.

Image source: Getty Images.

The product almost solely responsible for this was the UK-based company's star drug, Epidiolex, the net sales of which were more than $68 million during the quarter. Epidiolex, which treats certain forms of epilepsy, had just received FDA approval in Q2 2018, the major reason the company's sales were modest that quarter.

In terms of this most recent quarter's bottom line, GW Pharmaceuticals flipped to a profit this quarter of almost $80 million ($0.21 per share). The year-ago net loss was $84 million ($0.25).

However, the Q2 2019 result was tipped into the black due to a $104 million gain in the sale of a Rare Pediatric Priority Review Voucher. This is essentially a permit that allows for a quicker-than-average Food and Drug Administration (FDA) review of a qualifying drug candidate.

GW Pharmaceuticals is considered a marijuana stock because Epidiolex is derived from cannabis -- in fact, it is the first cannabis-derived medication to win approval in the U.S. The company said in the earnings release that it anticipates receiving approval for Epidiolex from European Union regulators in October.

The company added that its commercial organization is in place in the continent and is prepared for the product's launch in those markets. All told, so far in the U.S., more than 2,500 doctors have prescribed Epidiolex, and more than 12,000 patients have received it, according to GW Pharmaceuticals.

There was almost no bad news in the company's earnings report, and it seems investors are impressed by its prospects for the future. GW Pharmaceuticals stock was up nearly 12% in after-hours trading Tuesday night, giving it a fresh price spike in a year that's already had several surges, as the chart below shows.

GWPH Chart

GWPH data by YCharts.