The heroin injection scenes can be genuinely uncomfortable to watch, as they're filmed in the most realistic manner, with closeups of the needle penetrating the skin.
Bobby and Helen have an extremely toxic and unhealthy romance, with domestic violence playing a part in it. These scenes can be rather distressing to watch.
The scene where Helen's puppy escapes from her arms and accidentally jumps into the ocean from a boat can be particularly distressing to watch, especially for animal lovers.
The abortion scene can be gross and uncomfortable to watch for viewers (though we don't see the procedure itself being done, or the aftermath).