Cannabis has tripled in strength in three decades ago , scientists warn . They analysed levels of tetrahydrocannabinol ( THC ) in marijuana . Found THC concentrations of 30 % , compared to 10 % the last three decades . Scientists also discovered bacteria , fungi , butane and heavy metals in pot .
Cannabis has tripled in strength in the last three decades , scientists warn . They analysed levels of tetrahydrocannabinol ( THC ) in marijuana . Found THC concentrations of 30 % , compared to 10 % three decades ago . Scientists also discovered bacteria , fungi , butane and heavy metals in pot .