The hlc salt of medical grade heroin(90%> purity) can be injected without any complications whatsoever. But there's no such available purity on the market anymore or i doubt it'd ever been . Heroin divides in 3 grades, black tar, brown and white, the last have the form of crystals of certain shape and easily dissolves in the water without precipitate or coloration of the solution, the first two sold in form of powder usually diluted with some cut like sugar, salt, caffeine powder or sand or ground glass in worse cases and it's dangerous to inject the substance in this form without filtration due to fine-dispersed particles present in solution that can cause medical complications like inflammation, venous obstruction that occasionally lead to tissue necrosis and amputations in the worst cases. I think filtration is essential, adding some lemon juice helps in dissolving, ideally is to pass H cooked with citric acid through some makeshift filter like funnel and cheese cloth re-dissolve and filter again but i don't think it's necessary + some product will lost.
"Tianeptine has been intravenously injected by drug users in Russia.[79][80] This method of administration reportedly causes an opioid-like effect and is sometimes used in an attempt to lessen opioid withdrawal symptoms.[79] Tianeptine tablets contain silica and do not dissolve completely. Often the solution is not filtered well thus particles in the injected fluid block capillaries, leading to thrombosis and then severe necrosis. "