One of the main things the British did was prevent the Qing government from taxing the product. We've seen with tobacco and alcohol that sin taxes can be very e

One of the main things the British did was prevent the Qing government from taxing the product. We've seen with tobacco and alcohol that sin taxes can be very effective. You can also regulate marketing, which has also been effective with alcohol and tobacco. Arguably the root of current opiod crisis was a failure to regulate marketing of opiods which caused doctors to over prescribe them.