Our provision for returns was $3.0 million at September 30, 2022, compared to $3.2 million at December 31, 2021. The decrease is primarily due to lower sales for certain products.
The provision for coupons was $2.0 million at September 30, 2022 compared to $5.0 million at December 31, 2021. The decrease is primarily due to the decrease in sales specifically for Targadox, as a result of continued generic competition and to a lesser extent, the timing of payments from December 31, 2021.
Our managed care rebate provision was $3.7 million at September 30, 2022 compared to $3.5 million at December 31, 2021. The increase is primarily due to incremental provisions resulting from our newly launched products, Qbrexza, acquired and launched during the second quarter of 2021, as well as the acquisition and launch of Amzeeq and Zilxi in January 2022, and to a lesser extent, a greater portion of sales qualifying for managed care rebates.
Our government rebate provision was $0.9 million at September 30, 2022 compared to $0.7 million at December 31, 2021. The increase is primarily due to incremental provisions resulting from the acquisitions of Amzeeq and Zilxi in January 2022.
Cost of Goods Sold
Cost of goods sold increased by $0.5 million, or 2%, to $23.1 million for the nine-month period ended September 30, 2022, from $22.6 million for the nine-month period ended September 30, 2021. The increase is primarily due to higher product cost of goods sold of $2.1 million driven by our increased net product sales from period-to-period, increased amortization of $1.1 million related to our acquired intangible assets from the acquisition of Amzeeq and Zilxi in January 2022, and costs of approximately $1.1 million related to freight, product validation and stability testing for Amzeeq and Zilxi. The above increases to cost goods sold from period-to-period are offset, in part, by a decrease as the nine-month period ended September 30, 2021 included an inventory step-up of $4.2 million for inventory units sold related to the acquired finished goods of Qbrexza in 2021.
Research and Development
Research and Development expense increased to $6.7 million for the nine-month period ended September 30, 2022 from $0.8 million for the nine-month period ended September 30, 2021. The increase is related to clinical trial expenses to develop our DFD-29 product, for which dosing began in March 2022. We expect these expenses to increase as additional patients are enrolled into the two Phase 3 trials as well as the other associated cost of the development program.
Research and Development - licenses acquired
Research and development expenses - licenses acquired decreased $13.8 million, or 100%, from the nine-month period ended September 30, 2021. The nine-month period ended September 30, 2021 reflects the acquisition of our development stage asset from DRL for $10.0 million and the fair value of the contingent payment due DRL of $3.8 million.
Selling, General and Administrative
Selling, general and administrative expenses increased $20.1 million, or 84%, to $45.5 million for the nine-month period ended September 30, 2022, from $24.8 million for the nine-month period ended September 30, 2021. The increase is primarily attributable to the expansion of our salesforce, marketing expenses related to the expanded product portfolio of our four products, additional headcount costs, including non-cash stock compensation expenses, legal expenses and compliance and other professional fees associated with being a public company.
Interest Expense
Interest expense decreased $1.5 million to $1.4 million for the nine-month period ended September 30, 2022, from $2.9 million for the nine-month period ended September 30, 2021. The nine-month period ended September 30, 2021 includes dividends and interest on our convertible preferred shares that converted into common stock upon the closing of our IPO in November 2021.