Any adult 21 years or older is allowed to purchase up to 1 ounce (28 grams) in a single transaction (previously, tourists were restricted to only 7 grams per transaction), however they may possess up to 2 ounces. Medical patients are allowed to posses up to 2 ounces, or 40g of concentrate, or 20,000mg in other infused forms (such as edibles). Larger amounts for possession are permitted to medical patients granted extended plant counts for severe illnesses.
It’s important to remember that these regulations apply to sales, not possession. As per the Colorado Constitution, you are allowed to legally posses 1oz (or 28g) of THC.