That could result in blood clots or other problems.

Depending on particle size, the biggest problem could be it getting stuck in various capillaries all over the body. If he injected into an artery, it would first flow out into the body, to wherever that specific artery was feeding, splitting into smaller and smaller blood vessels ... until it finally reached blood vessels so tiny that the particle of powdered gold couldn't fit through, where it would get stuck and then indefinitely clog the tiny capillary. All the blood your heart pumps must pass through a capillary somewhere before it can go back for another trip around. If he injected into a vein, pretty much the same result, except a lot of it would end up getting stuck in the lungs first.

As for what exact effects that would cause... In tiny amounts, it probably wouldn't do anything noticeable. A blocked capillary here or there isn't that big of a deal. The body will heal around it and reroute new capillaries to serve that area instead; if a small amount of tissue around the capillary dies, it will be removed by the immune system and healed over. In larger doses, though, I figure you'd see the same kind of circulatory effects that come from untreated diabetes -- extremities like the fingers and toes dying and then going necrotic; numbness; loss of eyesight... Probably permanent and irreversible as well, since there's no way to remove the gold particles from those capillaries without destroying them in the process, which would only make the damage worse.

For anyone else thinking of injecting themselves with gold:

1. Don't.

2. Only do extremely small amounts at a time. Micrograms. Fractions of a microgram.

3. Be sure to use extremely tiny particles -- nano-scale stuff. You want particle sizes that are smaller than a single human cell. And hope the particles don't clump together.