Which prescription pills will increase the likelihood of a stroke?

Usually not problem: But, in elderly, anti-psychotic drugs of all sorts, older such as thorazine, newer such as seroquel, (quetiapine) can increase risk of TIA or stroke. Also, high doses of sympathomimetic drugs such as amphetamines can do this. In general, drugs which create vascular risks are withdrawn from market. One caveat, anti-hypertensives which cause low blood pressure can contribute to stroke in that way.