The Consumer Cannabis Act (KCanG) distinguishes between adults aged 21 and over and young adults aged 18 to 20. Cultivation associations may pass on no more than 25 grams a day and 50 grams a month to adults aged 21 and over. To young adults, they may pass on no more than 30 grams a month, and the cannabis may contain no more than 10 per cent THC (§ 19 para. 3 KCanG).
The reason: the brain continues to mature until around the age of 25. Until then, according to the Federal Ministry of Health, children, adolescents and young adults are particularly vulnerable to the psychological, physical and social consequences of cannabis, with long-term but also with short-term use. The more THC, the greater the risk of dependence and mental health problems. The limit is meant to reduce this risk for young adults.
The risk does not disappear on your 21st birthday; the brain continues to mature for a few more years. Under 18, cannabis is prohibited altogether. And in road traffic, the rule at the wheel under 21 is: no THC at all.
Remember: The younger you are, the more careful you should be. Starting later and keeping THC low reduce the risk the most.
More on this: Why age matters