Cannabis has been used as a medicinal plant for thousands of years. But the cannabis of today is different from the cannabis of thousands of years ago. Selective breeding over centuries, and especially in the last 50 years, resulted in growers prioritizing psychoactive strength.
Like any medicine, the right type and quantity needs to be selected, it must be used with the correct frequency, and some people should not use it all on account of contraindications.
More concerning health effects are coming up that appear to be linked to this high potency and frequent recreational use. This doesn’t detract from any medical benefits the plant has, but it does make it clear that misuse comes with consequences.
E.g., see the recent papers listed at Science Daily. The ones making the news more recently were about the increased chance of a heart attack.