result of amortization of inventory step up and acquired technology following the acquisition of Upright amounting $526. Gross profit excluding these amortizations was $1,607 (44.7% of revenues).
Research and Development Expenses
Our research and development expenses increased by $1,424, or 116% to $2,655 for the three months ended March 31, 2021, compared to $1,231 for the three months ended March 31, 2020. This increase was mainly due to the consolidation of Upright during the three months ended March 31, 2021.
Research and development expenses consist mainly of payroll expenses to employees involved in research and development activities, expenses related to our Dario and Upright software application and related devices, labor contractors and engineering expenses, depreciation and maintenance fees related to equipment and software tools used in research and development, Dario’s clinical trials performed in the United States to satisfy the FDA product approval requirements and facilities expenses associated with and allocated to research and development activities.
Sales and Marketing Expenses
Our sales and marketing expenses increased by $3,041, or 74.3% to $7,132 for the three months ended March 31, 2021, compared to $4,091 for the three months ended March 31, 2020. This increase was mainly due to the consolidation of Upright during the three months ended March 31, 2021.
Sales and marketing expenses consist mainly of payroll expenses, online marketing campaigns of the Dario service offering, trade show expenses, customer support expenses and marketing consultants and subcontractors.
General and Administrative Expenses
Our general and administrative expenses increased by $50, or 0.9%, to $5,621 for the three months ended March 31, 2021, compared to $5,571 for the three months ended March 31, 2020. This increase was mainly due to a net increase in our various general and administrative expenses which also includes the consolidation of Upright.
Our general and administrative expenses consist mainly of payroll and stock-based compensation expenses for management, employees, directors and consultants, legal fees, directors’ and officers’ insurance, patent registration, expenses related to investor relations, as well as our office rent and related expenses.
Financial (Income) Expenses, net
Our financial expenses, net for the three months ended March 31, 2021, were $639, an increase of 388%, compared to financial income of $222 for three months ended March 31, 2020. This increase was mainly due to foreign currency translation differences.
Financial (income) expenses, net mainly include bank charges, interest income, lease liability and foreign currency translation differences.
Net loss
Net loss increased by $5,074, or 51.3%, to $14,966 for the three months ended March 31, 2021, compared to a net loss of $9,892 for the three months ended March 31, 2020. The increase in net loss for the three months ended March 31, 2021, compared to the three months ended March 31, 2020, was mainly due to the increase in our operating expenses and the consolidation of Upright.
Non-GAAP Financial Measures
The factors described above resulted in net loss attributable to common stockholders of $15,510 and $11,167 for the three months ended March 31, 2021 and 2020, respectively.