Selectivity Memes

The biochemistry betrayal is real! This meme perfectly captures how our blood-brain barrier (BBB) plays favorites with molecules. Caffeine and alcohol get VIP access to the brain because they're lipid-soluble compounds that can slip through the BBB's phospholipid membrane like they own the place. Meanwhile, the barrier is stopping those same lipids from entering! The BBB is essentially that selective bouncer who's like "You can come in, but your friend has to stay outside" despite them wearing nearly identical outfits. Fun fact: the BBB is so selective it blocks approximately 98% of all small-molecule drugs and virtually 100% of large-molecule therapeutics from reaching the brain. Talk about being picky with the guest list!