Summary Non‐orthogonal multiple access (NOMA) has been investigated as a promising multiple radio access technology for future wireless networks to enable massive connectivity and improve spectral efficiency (SE). Furthermore, energy efficiency (EE) is becoming a primary concern and an inevitable trend for future wireless networks. For this, recent works have been provided good thoughts into joining these two conflicting performance metrics EE and SE. The joint EE–SE trade‐off problem for multi‐user NOMA systems in downlink is studied in this paper. The mathematical formulation of the EE–SE trade‐off is given as an optimization issue subject to some constraints. The basic thought is to improve EE by imposing simultaneously a minimum SE to be satisfied. The quality of service (QoS) requirement for each user is also provided to ensure optimality. For this, a dynamic energy‐efficient power allocation is proposed. Then, an iterative optimization algorithm with low computational complexity is developed to reach the proposed power allocation. Simulations have been conducted and compared to existing NOMA systems to show the effectiveness of the suggested approach in terms of EE and SE.