Primarex 100 contains methenolone enanthate, a long-acting methenolone ester producing a rapid onset of serum methenolone with a continued duration of action of 5 to 8 days after IM injection. Primarex 100 is moderately anabolic and androgenic. Methenolone is considered one of the safest anabolic agents, producing quality gains in muscle size and appearance.