elevated Harmony’s visibility among investors and provided the financial resources that we believe will allow us to continue to support our commercialization efforts for WAKIX, advance our clinical programs, and pursue the acquisition of additional assets that would be complementary to our existing commercial footprint and core areas of expertise.”
Mr. Jacobs added, “With FDA approval of the cataplexy indication for WAKIX and despite the COVID-19 pandemic, WAKIX sales posted double-digit, quarter-over-quarter growth. I am grateful to our employees who met the challenge of achieving these goals during a disruptive global pandemic. Looking ahead, our Phase 2 trial in patients with Prader-Willi Syndrome is actively enrolling patients and our clinical team has made good progress toward the initiation of two additional clinical trials, one in patients with myotonic dystrophy and another in pediatric narcolepsy patients.”
Fourth Quarter 2020 Financial Results
For the three-month period ended December 31, 2020, Harmony reported net product revenue of $56.3 million, compared to $6.0 million for the same three-month period in 2019. The increase was primarily due to growing sales of WAKIX, which first became commercially available in November 2019, and the label expansion to include cataplexy in patients with narcolepsy that occurred on October 13, 2020.
For the three-month period ended December 31, 2020, Harmony reported net loss of $0.2 million, or $0.00 per diluted share on a U.S. generally accepted accounting principles (GAAP) basis.
For the three-month period ended December 31, 2020 and 2019, a comparison of total operating expenses is not meaningful and not included in this commentary as WAKIX did not become commercially available for the treatment of EDS in adult patients with narcolepsy until November 2019.
Full Year 2020 Financial Results
For the twelve-month period ended December 31, 2020, net product revenue grew to $159.7 million, compared to $6.0 million during the same twelve-month period in 2019. The increase was primarily due to growing sales of WAKIX following the drug’s initial FDA approval in November 2019 as a treatment for EDS in adult patients with narcolepsy and the label expansion in October 2020 to include cataplexy in adult patients with narcolepsy.
For the twelve-month period ended December 31, 2020, total operating expenses were $115.0 million compared to $150.3 million for the same twelve-month period in 2019. The decrease was primarily driven by a decrease in R&D expenses related to payment of a $50 million milestone to Bioprojet, partially offset by an increase in sales and marketing and general and administrative expenses related to the commercial launch of WAKIX.
For the twelve-month period ended December 31, 2020, Harmony reported a net loss of $36.9 million, or $2.48 per diluted share on a GAAP basis. For the same period, non-GAAP adjusted