Stud 100 desensitizing spray for men also known as premjact, makes sex last longer by prolonging the time it takes the man to ejaculate, or reach orgasm. Stud 100 desensitizing spray for men stud 100 desensitizing spray for men containscontains the active substance lidocaine. Lidocaine is a local anaesthetic which is used to reduce the sensitivity to touch of the penis just before intercourse sex. The reduction in sensitivity helps to delay ejaculation climax in cases of over rapid or premature ejaculation coming to a climax too quickly.