I think the higher rates of sensitivity to medicines is because of MCAS. It's a newly discovered condition that hardly any doctors have ever heard of since there weren't any diagnostic criteria until 2010 and it's hard to diagnose. Some estimate that as many as 17% of the general population and 50% of those who are autistic have MCAS.
"Mast cell activation syndrome (MCAS) is a complex disorder hallmarked by chronic multisystem inflammatory, allergic and growth dystrophic phenomena caused by inappropriate mast cell activation. MCAS has been estimated to affect as many as 17% of the population with a severity ranging from mild to life-threatening. MCAS patients are more sensitive than the average person to chemicals in the environment, including the nondrug ("inactive") ingredients (excipients) in medications and supplements. Excipient reactivity may explain unusual side effects to medications health professionals often find puzzling, such as the patient who appears intolerant of prednisone, acetaminophen, levothyroxine, or a vitamin"
Recognition and Management of Medication Excipient Reactivity in Patients With Mast Cell Activation Syndrome - PubMed