Biomedical is a very loose term that means different things to different people.
In practice, most people use the term to refer to a group of interventions which are designed to stop, or at least reduce, the effect of biomedical problems (such as gastrointestinal abnormalities, immune dysfunctions, detoxification abnormalities, and/or nutritional deficiencies or imbalances).
The supporters of biomedical interventions believe that these biomedical problems act as triggers which cause, or make worse, many of the problems faced by autistic people. They believe that those problems can be solved, or at least reduced, by following one or more biomedical interventions.
There is a vast range of biomedical interventions, many of which are considered to be forms of complementary or alternative medicine by most traditional health care practitioners. Biomedical interventions include diets, nutritional supplements and hormones, the "off-label" use of some medications, as well as practices such as chelation and hyperbaric oxygen therapy.
Please bear in mind that many biomedical interventions (such as glutathione) will fall into more than of these categories.
Some autistic people may have one or more physiological problems but it is unclear how many autistic people have these problems. It is also unclear if these problems cause or worsen the features of autism and related issues, if they arise because of the autism, or if they are completely unrelated to the autism.
The quality of evidence for biomedical interventions varies enormously. For example, most medical procedures currently have very little high-quality research evidence supporting them when they are used as alternative or ‘off-label’ treatments for autistic people. Research shows that some medical procedures (such as hyperbaric therapy) are not effective interventions for the treatment of autistic people.
The risks and safety of biomedical interventions varies enormously. For example, most medical procedures carry some risk and this risk is likely to be higher when that procedure is used in an off-label way to treat autistic people, mainly because of the lack of regulation and agreed protocols. Some off-label medical procedures such as chelation may pose significant health risks to some autistic people.