The answer, to be honest, seems like a fairly strong .... Yes, it can !
Many herbal remedies for high blood pressure contain extracts of garlic along with other preparations - such as holly leaf, holly berry, daikon seeds, ginseng and other similar products.
All of these have been shown to be active and effective but garlic in particular seems to be pretty powerful in its action. You can read extended details of press reports and research about garlic here - but in summary below, here are the details:
The published studies have been pulled together into a meta analysis - a big overview of all the information. Most studies looked at concentrated garlic preparations. The outcomes were fairly conclusive in showing good reductions in blood pressure levels with the garlic treatments. Most of the research papers compared garlic to a placebo capsule and found a significant difference.
When the scientists looked at the studies of people who were known to have high blood pressure they found that garlic lowered the systolic blood pressure reading by about 8 and the diastolic by about 7.
The higher a persons blood pressure was at the start of the study, the more reduction they got from the garlic.
These results are obviously very encouraging.
Other research looking at Alistrol - details to the right of this page - also show significant blood pressure reductions in most people who use it. Alistrol contains garlic mixed with other active blood pressure herbal preparations.
It's my own view that natural blood pressure remedies often have a lot to offer - but I think they work best alongside other strategies or along side normal blood pressure medications.