Medical research and teaching still default to treating patients as cis men. However, there are many differences between the sexes, both biological (e.g. anatomy, hormonal balance) and socio-cultural (e.g. lifestyle, stereotypes). These differences influence how diseases develop, are diagnosed, progress and are treated, and lead to side effects and dosage problems with medications.

Drugs are processed and work differently and would require gender-specific dosing. Cis women are twice as likely to suffer adverse side effects, and the second most common reaction is a lack of effect. Trials are still too rarely analysed specific for sex and gender, the classic test subject remains male.

Diseases are also standardised as 'women's diseases' or 'men's diseases'. The symptoms of the other sex are then unknown or atypical, and diagnosis is distorted and delayed.
For example, women are more likely to report secondary symptoms such as nausea and dizziness when they have a heart attack. As a result, their heart attacks are more likely to go undetected and they are more likely to die as a result.
The autism and ADHD diagnosis is also a male model; the diagnosis is based almost exclusively on cis-male study data. Girls and women can show completely different symptoms and hide them better due to socialization.
For other illnesses, particularly mental illnesses, the problem is reversed. For example, although the symptoms of depression can vary greatly, common diagnostic questionnaires refer only to female symptoms. Men are diagnosed more poorly and late, and their suicide rate is three times higher.

Stereotypes and expectations also influence treatment. Cis-men with the same severity of symptoms are examined and treated more intensively and their symptoms are interpreted as organic, whereas women's symptoms are perceived as more psychosocial, even hysterical. They were given sedatives after the same operation, whereas men were more likely to be given painkillers.