A needleless injection device including: - a body forming a housing which extends axially from an upper radial seat , along an injection axis (B), - a gas generator , - a tubular reservoir which contains an active ingredient and which extends axially in said housing from an upper end to a lower end , and - a nozzle for injecting the active ingredient which is arranged at the lower end of the reservoir , and which has an external thread adapted to be screwed onto a complementary internal thread formed by the body , the injection device being characterized in that it comprises a membrane comprising a radial annular disc which is interposed axially between said upper end and said upper radial seat , and a tubular part which extends axially into the reservoir , from the annular disc , and in that the thread of the nozzle has a generally triangular section, said thread being delimited by an upper face which has a first angle (A1) with respect to a radial axis (C) perpendicular to the injection axis (B), and a lower face which has a second angle (A2) with respect to said radial axis (C), and in that the first angle (A1) is greater than the second angle (A2), the thread being of the sawtooth type, the second angle (A2) formed by the lower face of the nozzle being non-zero so that said lower face forms a flank. - a body forming a housing which extends axially from an upper radial seat , along an injection axis (B), - a gas generator , - a tubular reservoir which contains an active ingredient and which extends axially in said housing from an upper end to a lower end , and - a nozzle for injecting the active ingredient which is arranged at the lower end of the reservoir , and which has an external thread adapted to be screwed onto a complementary internal thread formed by the body , the injection device being characterized in that it comprises a membrane comprising a radial annular disc which is interposed axially between said upper end and said upper radial seat , and a tubular part which extends axially into the reservoir , from the annular disc , and in that the thread of the nozzle has a generally triangular section, said thread being delimited by an upper face which has a first angle (A1) with respect to a radial axis (C) perpendicular to the injection axis (B), and a lower face which has a second angle (A2) with respect to said radial axis (C), and in that the first angle (A1) is greater than the second angle (A2), the thread being of the sawtooth type, the second angle (A2) formed by the lower face of the nozzle being non-zero so that said lower face forms a flank. the injection device being characterized in that it comprises a membrane comprising a radial annular disc which is interposed axially between said upper end and said upper radial seat , and a tubular part which extends axially into the reservoir , from the annular disc , and in that the thread of the nozzle has a generally triangular section, said thread being delimited by an upper face which has a first angle (A1) with respect to a radial axis (C) perpendicular to the injection axis (B), and a lower face which has a second angle (A2) with respect to said radial axis (C), and in that the first angle (A1) is greater than the second angle (A2), the thread being of the sawtooth type, the second angle (A2) formed by the lower face of the nozzle being non-zero so that said lower face forms a flank. <EOS>