While more research is needed to find the recommended dosage of turmeric, randomised control trials (RCT) have used a similar dosage to one another. This meta-analysis found that 8 RCTs used around 1g/day when given without painkillers and 500mg/day when given alongside painkillers. The highest dosage given was around 2g/day for joint pain. See your doctor to get an approximate dosage for your joint pain.
There are other turmeric extracts that contain Labdane type Diterpene, such as in Japanese White Turmeric. Research is ongoing to establish the optimal dosage, but there are some supplements with patents that extract the Diterpene for your consumption.