I'll take the opposite stance.
I think that Freddie didn't do heroin. I think he was selling it because it's popular right now, and his mom is a heroin addict. That way he could keep her supplied at little to no cost.
Freddie was a dope smoker, not a horse freak.
If we assume that he swallowed the drugs (when he ducked into a building temporarily and just prior to being caught) then the effects of an OD might help explain his reaction while in the police van.
Oh, by the way, I’m not certain the guy seen running past the camera, then into the building is Freddie. Freddie was wearing a rather distinctive jacket when captured, and that runner appears to be in a black hoodie. It’s possible that’s the other guy who was running, which would also explain why he’s not seen coming out of the building again. The timing’s also not quite right for running down the street, across the courtyard, into the apartment, then back out and a block north to where Freddie was grabbed. The police radio traffic shows that all took place within a minute, with the first officer saying “I got him” 40 seconds after the pursuit was called out.