What are the negative effects or side effects of microdosing?

In the Thomas Anderson study, the top 3 most commonly reported challenges were:

Concerns about legality (this ranked first by a significant margin)
Physical Discomfort, such as upset stomach
"Other Concerns" about the long-term consequences of microdosing, due to lack of scientific research
In general, the most commonly reported side effects from microdosing includes:
Muscle cramps
Upset stomach
Dizziness
Anxiety
Overstimulation
Irritability or agitation on "off" days
Paranoia (related to the legality)

Todo:: cite sources