The invention relates to a needleless injection device having a body (12), which forms a receptacle extending axially from an upper radial seat along an injection axis, a gas generator, a tubular reservoir (24) which contains an active principle and which extends axially in said receptacle from an upper end as far as a lower end, and a nozzle (28) for injecting the active principle (26), which nozzle (28) is arranged at the lower end of the reservoir (24) and has an outer thread (72) designed to be screwed onto a complementary female thread (74) formed by the body (12), the injection device (10) being characterized in that the thread (72) of the nozzle (28) has overall a triangular cross section, said thread (72) being delimited by an upper face, which has a first angle with respect to a radial axis perpendicular to the injection axis (B), and a lower face, which has a second angle with respect to said radial axis, and in that the first angle is greater than the second angle.
