As I wrote in another thread, there is no obvious reason why an immaterial substance can't stand at one end of a causal relation and a material substance at another, or why an immaterial substance can't actualize a potentiality in a material substance, or why (given some other account of causation like, e.g., counterfactual dependence) an immaterial substance can't cause an effect in a material one. The only exceptions I can think of right now are physicalist energy transfer and (maybe) Regularity theories of causation.

John West wrote:

I should copy Armstrong's version of the interaction problem some time (A Materialist Theory of the Mind). He freely admits that the conceptual versions of the problem aren't very serious. He's more worried about the empirical versions. I think this stance is at least somewhat common in the non-dualist literature. (I seem to remember Lowe saying something to the same effect in one of his books.)

I think that's right. A lot of non-dualists think that anyone who rejects causal closure of the physical will eventually be skewered by empirical results.

Presumably, that we won't find energy transfers in the brain that don't have a physical cause.

Apart from the fact such a conclusion is speculative - we are certainly not in a position to claim that now - it seems open to question whether dualism requires mental to physical causation to work in such a way.

Also, there are empirical arguments against materialist theories of mind.

Yes, those are two of the main ones, except that placebo/nocebo effects are part of a far wider class of phenomena known as psycho-physical causation. Placebo/nocebo are amongst the varieties of these phenomena that seem the least inexplicable from a materialist perspective (though they are so far without a full naturalistic explanation, and it seems to me unlikely they ever will have). There are quite a few other varieties of psycho-physical causation that seem even more puzzling from a naturalistic viewpoint, such as cases of hypnotic and hysterical suggestion. Some cases of such suggestion, like that of Olga Kahl, seems in principle to defy physiological explanation. There are also some interesting phenomena involving what seems to show the effect of one person's mental processes on another person's body (although often it is hard to rule out autosuggestion). Maternal impressions are an example, like the woman who saw where a man had, had his penis removed due to a tumour (a rare occurrence) and then gave birth to a son whose penis was missing (a nearly unheard of birth defect).

Aspects of automatism, memory, genius, creativity, NDEs and OBEs (ignoring for a second veridical cases and just focusing on the fact they seem to show profoundly lucid awareness at a time when the brain is shutting down or has shut down) also push naturalistic explanations of the mind to breaking point. For some of these the issue isn't so much that they violate naturalism per se, but that they seem to violate how contemporary neuro- and cognitive-science see the brain/mind working, and no other kind of naturalism seems viable today.

Then, finally, there is the evidence of psychical research /parapsychology. Of course, most materialists are even less likely to accept this evidence than they would the claim of the immateriality of the mind itself. But it remains the case the evidence is strong, if not perhaps completely coercive.