Would taking 1000mg garlic tablet a day help decrease blood pressure? is the higher dose the better?

There is some: anecdotal evidence (based on personal stories, not science!) that 600-900 mg of garlic (in tablet form) daily may lower one's blood pressure modestly. But many other non-drug treatments work better: Healthy diet low in fat, salt, high in fruits/veggies. Weight loss, if needed. Regular/daily physical activity. Stress reduction. Relaxed breathing, Meditation. Yoga. Tai Chi. Try those!