. Labs Testosterone Heptylate is an injectable testosterone ester. A French pharmaceutical Company called Laboratoire Theramex are the main company worldwide which manufactures this compound and have been producing it under the name Testosterone Heptylate Theramex for many year, Labs have taken to produce this rare ester and have found an increase in popularity for this very long acting testosterone product .The compound Testosterone heptylate, like every injectable testosterone, has a strong androgenic & anabolic effect. Testosterone heptylate is amazing for the rapid buildup of strength and muscle gain. When looking at the gain rates of bodybuilders who use labs Testosterone Heptylate say milligram for milligram it seems to have a stronger & more pronounced effect than enanthate, cypionate,acetate and propionate.