General and Administrative Expenses
General and administrative expenses increased by $7.9 million, or 55.0%, for the three months ended June 30, 2022 and increased by $11.2 million, or 38.8%, for the six months ended June 30, 2022, as compared to the same periods in 2021. The increase in both comparable periods was primarily due to an increase to stock compensation associated with new awards, an increase in intangible asset amortization as a result of the $40.0 million milestone payment upon attaining $500.0 million in life-to-date aggregate net sales of WAKIX in the United States and an increase in personnel costs.
Interest Expense, Net
Interest expense decreased by $3.3 million, or 45.7%, for the three months ended June 30, 2022 and decreased by $6.3 million, or 43.6%, for the six months ended June 30, 2022, compared to the same periods in 2021 primarily due to lower interest rates as a result of entering into the Blackstone Credit Agreement in August 2021, partially offset by an increase in amortization of deferred financing costs.
Income Taxes
For interim periods, we estimate the annual effective income tax rate and apply the estimated rate to the year-to-date income or loss before income taxes. The effective income tax rate was 19.5% and 12.3% for the three months ended June 30, 2022 and 2021, respectively, and 14.4% and 8.4% for the six months ended June 30, 2022 and 2021, respectively. The increase in the effective income tax rate for both comparable periods was primarily driven by an increase in taxable income. Currently, we have recorded a full valuation allowance against our net deferred tax assets, primarily related to federal and state net operating losses.
Liquidity, Sources of Funding and Capital Resources
Overview
To date, we have financed our operations primarily with (a) proceeds from sales of our convertible preferred stock; (b) borrowings under our (i) CRG Loan, (ii) our Credit Agreement with OrbiMed and (iii) our Blackstone Credit Agreement; (c) the proceeds from our IPO; and (d) the proceeds from the sale of common stock to Blackstone. From our inception through our IPO, we received aggregate proceeds of $345.0 million from sales of our convertible preferred stock. In August 2020, we completed the IPO of our common stock, in which we sold 6,151,162 shares of our common stock, including 802,325 shares of our common stock pursuant to the underwriters’ over-allotment option. The shares were sold at a price of $24.00 per share for net proceeds of approximately $135.4 million. As of June 30, 2022, we had cash, cash equivalents, restricted cash and investments of $259.7 million and accumulated deficit of $408.6 million. As of June 30, 2022, we had outstanding debt of $198.5 million.
We have invested a portion of our available cash in money market funds, U.S. government and agency securities, corporate bonds and commercial paper in accordance with our investment policy. Our investment policy defines allowable investments and establishes guidelines relating to credit quality, diversification, and maturities of our investments to preserve principal and maintain liquidity. All investment securities have a credit rating of at least A-2/P-2/F2 from at least two National Recognized Statistical Rating Organizations. Our investment portfolio may be adversely impacted by future disruptions in the credit markets.
The unaudited condensed consolidated financial statements have been prepared as though we will continue as a going concern, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business.
We believe that our anticipated cash from operating and financing activities, including as a result of potential availability under the DDTL (defined below), existing cash and cash equivalents and investments will enable us to meet our operational liquidity needs and fund our planned investing activities for the next