US researchers say the jab was almost 96% effective in tests on around 270 men who were using it, with four pregnancies among their partners.
However, a relatively high number developed side effects, including acne and mood disorders.
Researchers have been investigating potential for male hormonal contraceptives for around 20 years.
They have all been looking for an effective way of suppressing sperm production without causing unpleasant or unbearable side effects.
