Thank you for participating in today's conference call to discuss Gelesis' results for the year ended December 31st, 2022. Joining us today are Yishai Zohar, founder and CEO of Gelesis, and Elliot Maltz, CFO of Gelesis. They'll be discussing the fiscal year 2022 financial results and providing business updates on the company's commercial products, Plenity. Before we begin today, I want to remind everyone this conference call may contain forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995, including statements related to Gelesis estimates and its future business outlook, prospects for financial results, including projected sales and EBITDA. Forward-looking statements generally can be identified by words such as anticipates, believes, estimates, expects, intends, plans, predicts, projects will likely result, and similar expressions.
The forward-looking statements are based on current expectations and assumptions that are subject to risks and uncertainties which would cause our actual results to differ materially from those reflected in the forward-looking statements. Factors that could cause or contribute to such differences include, but are not limited to, those discussed in our Form 10-K for the year ended December 31, 2022 that we filed with the Securities and Exchange Commission. All subsequent written and oral forward-looking statements attributable to Gelesis or persons acting on Gelesis' behalf are expressly qualified in their entirety by the cautionary statements included in this conference call. We undertake no obligation to revise or publicly release the results of any revision to these forward-looking statements except as required by law. Given these risks and uncertainties, listeners are cautioned not to place undue reliance on such forward-looking statements.
The following discussion may contain non-GAAP financial measures. For discussion and reconciliation of these non-GAAP financial measures, please see our earnings release for fiscal 2022. A webcast replay of this call will be available via Events and Presentation sections of the company's investor relations website at ir.gelesis.com. I would like to turn the call over Founder and CEO of Gelesis, Yishai Zohar. Yishai?
Thank you for joining us today. I last updated you in November that we were preparing to transition Plenity to over-the-counter or available without prescription. At this quarter, we officially began that process. We filed with the FDA in the first quarter. We expect to hear back in the third quarter. We have demonstrated there is a clear promotional response to Plenity and high satisfaction with 4 out of 5-star reviews on Trustpilot. Our estimates point to 2.5 x greater market size as a non-prescription product with 3x to 4 x better purchase efficiency for customers, higher gross margins, and broader distribution and partnership opportunities. Importantly, the switch to OTC could enable us to reach profitability with a smaller investment than previously projected. The tremendous momentum in the weight loss space presents a huge opportunity for Plenity.
Millions of Americans who are looking to lose 10-40 pounds are not served by the other treatment options due to label affordability or tolerability. We believe that Plenity is uniquely poised to address key concerns around affordability and tolerability. Plenity is priced affordably at $0.75 per dose or $98 per month. This plus data showing 6 out of 10 are responders who lost on average 10% of the weight or 22 pounds and 3.5 in of the waist in just 6 months, make Plenity uniquely poised to make a meaningful difference, and even more so as an OTC product. In clinical trials, Plenity had an unparalleled safety profile, and we have seen that replicated in our real-world experience of over 200,000 people as well.
People on Plenity describe how they are still able to eat the foods they love and feel satisfied with smaller portions. Our CFO, Elliot Maltz, will walk you through the financial highlights from the year.
Thank you, Yishai. During 2022, it was clear there was a direct promotional response to Plenity. When we advertised, we saw immediate uptake in new members and definitive growth. In order to preserve liquidity and concentrate our resources around making Plenity available over the counter, we significantly reduced our sales and marketing spend in the second half of 2022. I will now walk you through how we ended the year. Product revenue net was $25.6 million for the year ended December 31st, 2022, compared to $11.2 million in 2021, representing a year-over-year increase of 129%.
We acquired 121,500 new members during 2022 compared to 61,400 in the prior year, a 98% increase year-over-year, and sold twice as many units in 2022 compared to 2021. We achieved significant cost savings in manufacturing Plenity after validating our first commercial manufacturing line at the end of 2021 and saw the cost of goods sold on a unit level decrease as we expected. In light of reduced levels of investment in selling and marketing during the second half of 2022 and the shift in commercial strategy to make Plenity available over the counter, we recorded an inventory reserve of $13.3 million in 2022, which impacted gross margin.
Before accounting for the impact of this inventory reserve, our cost of goods sold was approximately $38 per unit sold in 2022 compared to an average net selling price of approximately $68 per unit. Net loss was $55.8 million. Adjusted EBITDA was negative $83.3 million in 2022 compared to net loss of $93.3 million and adjusted EBITDA of negative $73.8 million in 2021. Looking ahead to 2023, we plan to focus on transitioning Plenity to OTC, including the regulatory approval process with the FDA. We do not plan to invest significantly in marketing the prescription version of Plenity to new members during this time, but we will continue to support members taking the product.
We are confident this transition to OTC will be in the best interest of our shareholders as well as the patients we serve by significantly expanding access and removing costs associated with the prescription process. We are exploring a variety of options for commercializing Plenity, including strategic partnerships and geographic expansion. As funding is key to our operations, in February 2023, we completed a private placement of $5 million in convertible senior secured notes with an existing top-tier shareholder. We will need to continue raising capital as we go forward. In light of these circumstances, we will not be issuing guidance for 2023 at this time, but we'll update the market when we have more visibility into the commercial path of Plenity as an OTC product. Now I'll hand it back over to Yishai.
I'd like to end up by summarizing why 2023 should be a pivotal year for Plenity. We have proven in-demand commercial product that has generated $39.5 million in revenue since launch. Making Plenity available without a prescription significantly expands our market size and reduces our cost of acquiring those new members. Plenity is already approved as an OTC product in the EU, which presents an important opportunity for geographic expansion. We are also in the process of working with our commercial partner to gain regulatory approval in China. We're exploring using our proprietary technology for separate food products and food supplements, which present a potential additional partnering opportunities. There are exciting developments in the weight loss market, and we believe Plenity is uniquely able to benefit from them.
I'd like to thank everyone for listening to today's call. We look forward to speaking with you when we report our first quarter results. Thank you again for joining.