Consumption is legal, but planting, production, possession, trade, import, sale, handing out, and buying of any drug under the BtmG are all illegal without special license or exception. Such a medical exception exists for example for morphine in emergency medicine, or for diamorphine in drug rehabilitation, so a doctor can file a lot of paperwork to get a BtM-Rezept to get their patient one of those as a regular, very strict controlled medicine.
However, back to Bob at the party where Alice is handing out substances. Many street drugs (like Lysergic Acid Diethylamide or Benzoylmethylecgonine) are controlled under the BtM, and politics strives to keep the list of drugs up to date. Of the currently 455 chemicals, only 56 have exceptions under the BtMG. You can find LAD under the shorthand
lyse and Benzoylmethylegonine as
- Alice acquired the substances most likely by illegal production, import, or buying, as the two examples are not exeptable. However, she was not caught in the act, so no charge.
- Alice was in illegal possession of the substance till she gave it away. She was not caught in possession, so no charge.
- Alice also gave them to Bob, so she is guilty of handing them to Bob (Abgabe). This can be prosecuted if Bob 'rats her out'.
- Bob might be caught in possession the moment he is in the process of consuming it, but he'd most likely be only in possession of a single dose. That is most likely only a geringe Menge (small amount) that can be seen as too little to prosecute effectively and thus usually not prosecuted.
Alice is a heavy criminal now, but Bob? nothing to get him, at best