Usually the atypical antipsychotics are the most effective. What type of intrusive thoughts though? Different meds work for different situations. Like the above poster said, luvox is about the most effective med out there for OCD and it's an SSRI, Zyprexa is helpful both intrusive thoughts of any kind, has shown some efficacy in treating distortions associated with Anorexia. There's also Seroquel, Geodon, Latuda, Rexulti, Invega. There's a lot out there. It may take some trial and error, but odds are good you'll find something that helps.

Good luck.