@ Sandeep sharma,
Yes, gem therepy is effective only when you fulfil the following two conditions:
1. You should have faith on it
2. You should wear good quality gemstone
Although, you would require to energize the gemstones frequently as it is the main controlling element of gemstone.
Now, coming to your question of a “miracle cure“; I would say it can definitely cure a disease but can’t provide an instant relief. As we don’t inject it as medicine but it undergoes surface therapy (skin therapy). The vibes (rays) passing through the gemstone will interact with your body (and soul) and will start curing it. And this process takes some time.